wdiff draft-lior-radius-prepaid-extensions-11.txt draft-lior-radius-prepaid-extensions-12.txt

RADEXT A. Lior
Internet-Draft Bridgewater Systems
Expires: December 25, 2006
Intended status: Informational P. Yegani
Expires: December 31, 2007 Cisco
K. Chowdhury
Starent Networks
H. Tschofenig
Nokia Siemens Networks
A. Pashalidis
Siemens
NEC
June 23, 2006 29, 2007

Prepaid extensions Extensions to Remote Authentication Dial-In User Service
(RADIUS)
draft-lior-radius-prepaid-extensions-11.txt
draft-lior-radius-prepaid-extensions-12.txt

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This Internet-Draft will expire on December 25, 2006. 31, 2007.

Abstract

This document specifies an extension to the Remote Authentication
Dial-In User Service (RADIUS) protocol that enables service providers
to charge for prepaid services. The supported charging models
supported are volume-based, duration-based, and based on one-time
events.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 5
1.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6 7
1.2.1. Architectural Model . . . . . . . . . . . . . . . . . 7
1.2.2. Motivation . . . . . . . . . . . . . . . . . . . . . . 10 9
1.3. A simple use case . . . . . . . . . . . . . . . . . . . . 12
2. Supported Features . . . . . . . . . . . . . . . . . . . . . . 15
2.1. Multiple Concurrent Services . . . . . . . . . . . . . . . 15
2.2. Resource Pools . . . . . . . . . . . . . . . . . . . . . . 15
2.3. Complex Rating Functions . . . . . . . . . . . . . . . . . 17
2.4. One-time Charging . . . . . . Assumptions . . . . . . . . . . . . . . 17
2.5. Tariff Switching . . . . . . . . . . . . . . . . 11
1.4. Example Use Case . . . . . 18
2.6. Support for Roaming . . . . . . . . . . . . . . . . 11
2. Supported Features . . . 20
2.7. Dynamic Termination . . . . . . . . . . . . . . . . . . . 20
2.8. Querying 14
2.1. Services and Rebalancing . . Quotas . . . . . . . . . . . . . . . 20
3. Operations . . . . . . . . . . . . . . . 14
2.2. Resource Pools . . . . . . . . . . . 22
3.1. Authentication and Authorization Operation . . . . . . . . 22
3.2. Session Start Operation . . . 14
2.3. Rating Groups . . . . . . . . . . . . . . 24
3.3. Mid-Session Operation . . . . . . . . 16
2.4. Tariff Switching . . . . . . . . . . 24
3.4. Dynamic Operations . . . . . . . . . . . 17
2.5. Support for Roaming . . . . . . . . . 26
3.4.1. Unsolicited Session Termination Operation . . . . . . 26
3.4.2. Unsolicited Change of Authorization Operation . . . . 27
3.5. 18
2.6. Dynamic Termination Operation . . . . . . . . . . . . . . . . . . 27
3.6. Mobile IP Operations . . . . . . . . . . . . . . . . . . . 27
3.7. Operation Considerations for Multiple Services . . . . . . 28
3.7.1. Initial Quota Request . . . 19
2.7. One Time Event . . . . . . . . . . . . . 29
3.7.2. Quota Update . . . . . . . . . 19
2.7.1. One-Time Charging . . . . . . . . . . . . 29
3.7.3. Termination . . . . . . 19
2.7.2. Service Price Enquiry . . . . . . . . . . . . . . . 30
3.7.4. Dynamic Operations . 20
2.7.3. Balance Check . . . . . . . . . . . . . . . . . 30
3.7.5. Support for Resource Pools . . . 20
2.7.4. Refund . . . . . . . . . . . 30
3.7.6. One-time Charging . . . . . . . . . . . . . 21
3. Operations . . . . . 30
3.7.7. Error Handling . . . . . . . . . . . . . . . . . . . . 31
3.7.8. Accounting Considerations . 22
3.1. Capability Discovery . . . . . . . . . . . . . 31
3.7.9. Interoperability with Diameter Credit Control
Application . . . . . . 22
3.2. Authentication and Authorization Operation . . . . . . . . 22
3.3. Session Start Operation . . . . . . . 31
4. Attributes . . . . . . . . . . 23
3.4. Mid-Session Operation . . . . . . . . . . . . . . . . 33
4.1. PPAC Attribute . . 24
3.5. Dynamic Operations . . . . . . . . . . . . . . . . . . . . 33
4.2. 25
3.5.1. Unsolicited Session Termination Attribute . . Operation . . . . . . 26
3.5.2. Unsolicited Change of Authorization Operation . . . . 26
3.6. Termination Operation . . 34
4.3. PPAQ Attribute . . . . . . . . . . . . . . . . 26
3.7. Operation Considerations for Multiple Services . . . . . . 35
4.3.1. 27
3.7.1. Initial Quota Identifier AVP . . . . . . . . . . . . . . . . . 35
4.3.2. VolumeQuota AVP . . . . . . . . . . . . . . . . . . . 36
4.3.3. VolumeThreshold AVP . . . . . . . . . . . . . . . . . 36
4.3.4. DurationQuota AVP . . . . . . . . . . . . . . . . . . 36
4.3.5. DurationThreshold AVP . . . . . . . . . . . . . . . . 36
4.3.6. ResourceQuota AVP . . . . . . . . . . . . . . . . . . 36
4.3.7. ResourceThreshold AVP . . . . . . . . . . . . . . . . 37
4.3.8. Value-Digits AVP . . . . . . . . . . . . . . . . . . . 37
4.3.9. Exponent AVP . . . . . . . . . . . . . . . . . Request . . . . 37
4.3.10. Update-Reason AVP . . . . . . . . . . . . 27
3.7.2. Quota Update . . . . . . 37
4.3.11. PrepaidServer AVP . . . . . . . . . . . . . . . 27
3.7.3. Termination . . . 38
4.3.12. Service-ID AVP . . . . . . . . . . . . . . . . . . 28
3.7.4. Dynamic Operations . . 38
4.3.13. Rating-Group-ID AVP . . . . . . . . . . . . . . . . 28
3.7.5. Support for Resource Pools . 39
4.3.14. Termination-Action AVP . . . . . . . . . . . . . 28
3.7.6. One-time Charging . . . 39
4.3.15. Pool-ID AVP . . . . . . . . . . . . . . . 29
3.7.7. Error Handling . . . . . . 39
4.3.16. Pool-Multiplier AVP . . . . . . . . . . . . . . 29
3.7.8. Accounting Considerations . . . 39
4.3.17. Requested-Action AVP . . . . . . . . . . . 30

4. Attributes . . . . . . 39
4.3.18. Check-Balance-Result AVP . . . . . . . . . . . . . . . 40
4.3.19. Cost-Information AVP . . . . . 31
4.1. PrePaid Accounting Capability (PPAC) Attribute . . . . . . 31
4.2. Prepaid Accounting Operation (PPAQ) Attribute . . . . . . 40
4.4. 32
4.3. Prepaid Tariff Switching Attribute (PTS) Attribute . . . . . . . . . 41
4.4.1. VolumeUsedAfterTariffSwitch AVP . . . . . . . . . . . 42
4.4.2. TariffSwitchInterval AVP . . . . . . . . . . . . . . . 42
4.4.3. TimeIntervalafterTariffSwitchUpdate AVP . . . . . . . 42 39
5. Translation between RADIUS prepaid and Diameter Credit
Control . . RADIUS Interoperability . . . . . . . . . . . . . . . 43
6. Security Considerations . . . . . . . . . . 44
5.1. Session Identification . . . . . . . . . 44
7. Table of Attributes . . . . . . . . . 45
5.2. Translation between RADIUS prepaid client and Diameter
Credit Control AAA infrastructure . . . . . . . . . . . . 45
5.2.1. PPAC (c<->s) . . . . . . . . .
8. IANA Considerations . . . . . . . . . . . . 45
5.2.2. Service Termination Attribute (c->s) . . . . . . . . . 46
5.2.3. Quota Identifier Attribute (c<->s) . . . .
8.1. New RADIUS Attributes . . . . . . 46
5.2.4. Volume Quota Attribute (c<->s) . . . . . . . . . . . . 46
5.2.5. Duration Quota Attribute (c<->s) . . . . .
8.2. New Registry: Prepaid SubTypes . . . . . . 47
5.2.6. Resource Quota Attribute (c<->s) . . . . . . . . 46
8.3. New Registry: Update-Reason . . . 47
5.2.7. Value Digits Attribute (c<->s) . . . . . . . . . . . . 48
5.2.8. Exponent Attribute (c<->s) .
8.4. New Registry: Termination-Action . . . . . . . . . . . . . 48
5.2.9. Volume/Duration/Resource Threshold Attributes
(s->c) . .
8.5. New Registry: Requested-Action . . . . . . . . . . . . . . 48
8.6. New Registry: Check-Balance-Result . . . . . . . . 48
5.2.10. Update Reason Attribute (c->s) . . . . 49
8.7. New Registry: AvailableInClient-Extended . . . . . . . . 48
5.2.11. PrepaidServer Attribute (s<->c) . 49
9. Acknowledgements . . . . . . . . . . 50
5.2.12. Service-ID Attribute (s<->c) . . . . . . . . . . . . . 50
5.2.13. Rating-Group-ID Attribute (s<->c) .
10. References . . . . . . . . . 50
5.2.14. Termination-Action Attribute (s->c) . . . . . . . . . 50
5.2.15. Pool-ID Attribute (s<->c) . . . . . . . . 51
10.1. Normative References . . . . . . 51
5.2.16. Multiplier Attribute (s<->c) . . . . . . . . . . . . . 51
5.2.17. Requested-Action Attribute (c->s)
10.2. Informative References . . . . . . . . . . 51
5.2.18. Check-Balance-Result Attribute (s->c) . . . . . . . . 51
5.2.19. Cost-Information Attribute (s->c) . .
Appendix A. Example flows . . . . . . . . 52
5.2.20. VolumeUsedAfterTariffSwitch attribute (c->s) . . . . . 52

6. Security Considerations . . . . . . . 52
A.1. A simple flow . . . . . . . . . . . . 53
7. IANA Considerations . . . . . . . . . . 52
A.2. A flow with prepaid tariff switching . . . . . . . . . . . 54
8. Acknowledgements . . . . . . . . .
A.3. Resource pools and Rating Groups . . . . . . . . . . . . . 58
A.4. One-time charging . 55
9. References . . . . . . . . . . . . . . . . . . . 63
A.5. Price enquiry . . . . . . . 56
9.1. Normative References . . . . . . . . . . . . . . . 64
A.6. Balance check . . . . 56
9.2. Informative References . . . . . . . . . . . . . . . . . . 56 65
Appendix A. Example flows . . . . . . . . . . . . . . . . . . . . 57
A.1. A simple flow . . . . . . . . . . . . . . . . . . . . . . 57
A.2. A flow with prepaid tariff switching . . . . . B. Translation between RADIUS Prepaid and Diameter
Credit Control . . . . . . 60
A.3. Resource pools and Rating Groups . . . . . . . . . . . . . 64 67
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 71 76
Intellectual Property and Copyright Statements . . . . . . . . . . 72 77

1. Introduction

This document specifies an extension to the RADIUS protocol that
enables service providers to perform accounting and charging in an
"online" fashion. In particular, they enable the service provider to

(a) ensure that subscriber's remaining funds suffice before the
service is delivered, and

(b) interrupt service provision when the funds are exhausted.

Note that these capabilities are typically used in scenarios where
the subscriber maintains a prepaid account with the service provider;
hence, this extension is called the "prepaid" extension for RADIUS. Also note that the above capabilities are not
provided by the base RADIUS protocol.

It has been observed that subscribers prefer prepaid accounts to
postpaid ones
The functionality described in many circumstances. Indeed, it is expected that
offering a "prepaid mode of operation" will enabe service providers
to expand their existing customer bases. This this document is the main business
driver behind the extensions defined often referred as
"online charging" in this document. comparison to "offline charging" support
provided by RFC 2866 [RFC2866].

The extensions were designed with the following goals in mind. mind:

o Make use of existing infrastructure as much as possible (including
enabling the interworking of RADIUS-based and Diameter-based
infrastructures), and thereby limit the amount of necessary
capital expenditures,

o provide the ability to rate service requests in an "online"
fashion,

o provide the ability to charge the user's account prior to service
provision,

o protect against revenue loss, i.e. i.e., to prevent an end user from
obtaining service when the available funds do not suffice,

o protect against fraud, and

o be deployable over dialup, wired and wireless networks. for a number of services independent of the access
network technology.

The architecture between the entities that execute the RADIUS
protocols, with the extensions defined in this document, assumes that
the rating of chargeable events does not occur in the element that
provides the service. Instead, the rating may be performed at a
dedicated server, termed the "prepaid-enabled AAA server" or simply
"prepaid server". server" (PPS). Alternatively, the actual rating may occur
in an entity behind related to this prepaid server.

Furthermore, business logic may
dictate a time-dependent tariff model, for example that the price for
a service may switch at 8pm from a high to a low tariff. The
extensions defined in this document support such scenarios.

Furthermore, this document assumes an architecture where that a "quota server" is available
which, through co-ordination with the rating entity and a centralized an account
balance manager, is able to provide a quota indication for a
particular user when requested. This quota server may or may not
coexist in the prepaid server.

1.1. Terminology

o Network Access Server (NAS): As defined

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in RADIUS.

o this
document are to be interpreted as described in RFC 2119 [RFC2119].

Prepaid client Client (PPC):

The entity which triggers the RADIUS message exchange, including
the prepaid extensions defined in this document. The PPC typically resides in provides
the NAS.

o service to the users, and executes the RADIUS client which,
for the purposes of this document, is termed the "PrePaid Client"
(PPC). When the prepaid service is used the PPC collects service
event information and reports it while the services is provided to
the user. This event information is sent to the PPS using the
extensions defined in this document.

Prepaid Server (PPS):

The entity that interacts with the PPC using the RADIUS prepaid
extensions defined in this document.

Rating Entity:

This entity converts the credit that is allocated by the PPS into
a "quota". This quota is then returned to the requesting PPC via
the PPS. The rating entity may also determine that during service
provision a tariff switch will occur. In this case the rating
entity will include details of when exactly tariff switch will
occur.

Quota:

A quota denotes the amount of granted units to be consumed without
performing another credit control interaction.

Home Network:

The network which contains the user profile and the user's prepaid
account.

Authorize-Only Access Request:

A RADIUS message of type "Access Request" (code field=1) field = 1) that
contains a "Service-Type" AVP
(type=6) (type = 6) with value "Authorize-Only". "Authorize-
Only".

Offline Charging:

Offline charging is a process where charging information for
resource usage is collected concurrently with that resource usage.
The charging information is then passed through a chain of logical
charging functions. At the end of this process, Charging Data
Record (CDR) files are generated, which are then transferred to
the operator's billing domain for the purpose of subscriber
billing and/or inter-operator accounting (or additional functions,
e.g., statistics, at the operator's discretion). The billing
domain typically comprises post-processing systems, such as the
operator's billing system or billing mediation device. In
conclusion, offline charging is a mechanism where charging
information does not affect, in real-time, the service rendered.
[TS32240]

Online Charging:

Online charging is a process where charging information for
resource usage is collected concurrently with that resource usage
in the same fashion as in offline charging. However,
authorization for the network resource usage must be obtained
prior to the actual resource usage to occur. This authorization
is granted by the PPS upon request from the PPC. When receiving a
resource usage request, the PPS assembles the relevant charging
information and generates a charging event in real-time. The PPS
then returns an appropriate resource usage authorization. The
resource usage authorization may be limited in its scope (e.g.,
volume of data or duration), therefore the authorization may have
to be renewed from time to time as long as the resource usage
persists. Note that the charging information utilized in online
charging is not necessarily identical to the charging information
employed in offline charging. In conclusion, online charging is a
mechanism where charging information can affect, in real-time, the
service rendered and therefore a direct interaction of the
charging mechanism with the control of resource usage is required.
[TS32240]

1.2. Overview

This section provides an overview of the prepaid charging models and
architectures, which are supported by the extensions described in
this document.

A number of models of how to charge customers for data services in a
prepaid manner are supported, as follows. supported:

o Volume-based charging (e.g. (e.g., 2 Cents/KiloByte).

o Duration-based charging (e.g. (e.g., 3 Cents/minute).

o Subscription-based Resource-based charging (e.g. (e.g., 3 videos for 10 Dollars/month). Euros)

o Event-based charging (e.g. (e.g., 7 Cents/URL or email) Cents/ring tone) .

This draft assumes that the user maintains a prepaid account with his
home network. This account may be used to fund multiple services,
some of which may use the extensions defined in this document, and
some may use other mechanisms. The interworking of these mechanisms
is outside the scope of this document. Similarly, the means by which
the subscriber obtains funds is also outside the scope of this
document.

1.2.1. Architectural Model

The

This section describes the architectural model of the protocol
extensions described in this draft assumes that the
following entities are present in document. Figure 1 describes the network architecture.

o Service Access Device (SAD): This entity provides
involved entities.

The end user establishes a data service
to the users, and typically coincides connection with the NAS. The SAD
executes the RADIUS client which, for the purposes one of this
document, is termed the "PrePaid Client" (PPC). When the prepaid possibly multiple
PPCs during service is used access. The selected PPC communicates with a
HAAA server (directly or indirectly via a broker network).

The interface between the SAD collects service event information HAAA and
reports it while services are provided to the user. This event
information is sent to the PPS is implemented using the extensions defined in
this document.

o The PPS: The RADUIS server that supports
RADIUS protocol together with the prepaid extensions
defined described in this
document. If real-time credit control is
required, the PPC (SAD) contacts However, in cases where the PPS with service event
information included before does not implement the service is provided. The PPS
performs a credit check and allocates a portion of
RADIUS protocol, the available
credit implementation would have to map the service event.

o The rating entity: This entity converts the credit that is
allocated by the PPS into a time or volume amount, called the
"quota". This quota is then returned
requirements defined in this document to the requesting PPC (SAD)
(via the PPS). The rating entity may also determine that during
service provision a tariff switch will occur. In this case the
rating entity will include details of when exactly tariff switch
will occur. functionally equivalent
protocol.

The requesting PPC (SAD) meters the consumption of the service according to
the instructions provided by the PPS. After service completion, or
on reception of a subsequent request for service, the PPS deducts the
corresponding amount of credit from the user account. When a user
terminates an on-going service, the PPC informs the PPS with a
suitable indication about the unused portion of the allocated quota.
The PPS then refunds the user account accordingly. Note that
multiple PPSs may be deployed for reasons of redundancy and load
sharing. The system MAY may also employ multiple rating servers.

accounting
+------------+ +-----------+ protocol +--------------+
| User |<---------->|

Service AAA and
Element Prepaid
+----------+ +---------+ Protocol +----------+
| End |<---->|+-------+|<------------>| Home AAA |
| User | +->|| PCC || | IEEE 802.1x| Access |<------------>| Accounting Server |
| Device | PANA | Device |<-----+ || Client||<----+ | Server (HAAA) |
+------------+ IKEv2 +-----------+
+----------+ | +--------------+
... etc (PPC) |+-------+| | +----------+
| +---------+ | +--------------+
+------>| Prepaid ^
+----------+ |
prepaid | Server Protocol|
|
protocol +--------------+ End |<--+ | v
| User | | +----------+
+----------+ +------->| |
Prepapid | PPS |
Protocol | |
+----------+

Figure 1: Basic prepaid architecture Prepaid Architecture

The PPS and the accounting server in this architecture MAY may be
combined. The SAD PPC must have the ability to meter the consumption of
a prepaid data session. This metering is typically based on time
(i.e.
(i.e., seconds) or volume (i.e. (i.e., octets).

The device running the PPC may also have "Dynamic Session
Capabilities"
Capabilities", such as the ability to terminate a data session or to
change the filters associated with a specific data session by
processing "Disconnect" messages and "Change of Authorization"
messages as per RFC 3576. 3576 [RFC3576].

This document assumes that the PPS is used as the AAA server. There
are three types of AAA server, as follows.

The AAA server in the home network (HAAA), which (HAAA) is responsible for
authentication of the subscriber. In addition, the HAAA communicates
with the PPS using the RADIUS protocol in order to authorize
subscribers.

o The AAA server in the visited network (VAAA) which exists only in
roaming scenarios and is responsible for forwarding the RADIUS
messages to the HAAA. The VAAA may also modify the messages.
Note that, in certain roaming deployments, the visited network may
be connected to the home network via one or more broker networks.

o The AAA server in one of the aforementioned broker networks
(BAAA), which is responsible for forwarding messages and does not
play an active role in the prepaid data service delivery. A BAAA
obviously exists only in those roaming deployments where the VAAA
and the HAAA are connected via the BAAA of a broker network.

This document assumes that the PPS communicates with the HAAA for the
purposes of authentication and authorisation. The PPS, in turn,
interfaces to entities which

o keep the subscriber's account balance (balance manager),

o rate access service requests in real-time (Rating Engine), (rating engine), and

o manage quota for a particular prepaid service (Quota Server). (quota server).

The above entities balance manager, the rating engine and the quota server belong to
the service provider's backend infrastructure and are outside the
scope of this specification. In particular, as far as this
specification is concerned, they are assumed to exist in the PPS. Three deployment scenarios are
presented in the remainder of this section. The first scenario is
depicted in Figure 2. In this scenario, the SAD, which runs the PPC,
the HAAA, and the PPS are located in the same provider network.

The subscriber's device establishes a connection with one of possibly
multiple SADs in the network. The selected SAD communicates with a
HAAA server (directly or indirectly).

The interface between the HAAA and the PPS is implemented using the
RADIUS protocol together with the extensions described in this
document. However, in cases where the PPS does not implement the
RADIUS protocol, the implementation would have to map the
requirements defined in this document to a functionally equivalent
protocol.

+------+ +-----+
| | | |
+--------+ +--------+ +--| HAAA |--+--| PPS |
| | | | | | | | | |
| Subscr.| | Service| | +------+ | +-----+
| |---| Access |--+ |
| Device | | Device | | +------+ | +-----+
| | | | | | | | | |
+--------+ +--------+ +--| HAAA |--+--| PPS |
| | | |
+------+ +-----+

Figure 2: Basic prepaid access architecture

The second scenario, depicted in Figure 3, is based on a static
roaming architecture that is typical of a wholesale scenario for
Dial-Up users or a broker scenario used in Dial-Up or WLAN roaming
scenarios.

+----+ +----+ +----+ +-----+
| | | | | | | |
+------+ +-------+ +-|VAAA|-+-|BAAA|-+-|HAAA|-+-| PPS |
| | | | | | | | | | | | | | | |
|Sub | |Service| | +----+ | +----+ | +----+ | +-----+
| |--|Access |-+ | | |
|Device| |Device | | +----+ | +----+ | +----+ | +-----+
| | | | | | | | | | | | | | | |
+------+ +-------+ +-|VAAA|-+-|BAAA|-+-|HAAA|-+-| PPS |
| | | | | | | |
+----+ +----+ +----+ +-----+

Figure 3: Static roaming prepaid architecture

Like in the basic prepaid architecture, the subscriber device
establishes a connection with the SAD. The SAD communicates with the
VAAA using the RADIUS protocol. The VAAA, in turn, communicates
using the RADIUS protocol with BAAA servers in the broker network.
There may be more than one Broker Network between the Visited Network
and the Home Network. The Home Network is the same as in the
architecture depicted in Figure 2.

Broker AAA (BAAA) servers MUST support the Message-Authenticator(80)
attribute as defined in RFC 2869. If they are used, they forward the
RADIUS packets as usual to the appropriate RADIUS servers.

Accounting messages are not needed to deliver a prepaid service.
However, accounting messages can be used to keep the PPS up to date up-to-date
as to what is happening with the prepaid data session. Therefore, a
BAAA SHOULD deliver RADIUS Accounting messages using the pass through
mode described in RFC 2866.

1.2.2. Motivation

Why not use existing RADIUS attributes to construct a protocol for
prepaid scenarios? This could lead to a solution where no code has
to be modified at existing devices.

It is indeed possible to construct a solution for prepaid scenarios
using existing RADIUS attributes. The RADIUS server would send an
Access-Accept message containing a Session-Timeout(27) and include a
Termination-Action(29) in the RADIUS-request. Upon receiving the
Access-Accept message, the NAS would meter the duration of the
session and upon termination of the session the NAS would generate an
Access-Request message again. The RADIUS server would then re-
authenticate the session and reply with an Access-Accept message
indicating the amount of additional time in a Session-Timeout(27).
Alternatively, it could respond with an Access-Reject message if
there were no more resources in the user account.

Moreover, if the user terminates the session prematurely, the NAS
could indicate this in the accounting stream so that unused funds can
be returned into the prepaid user account.

Unfortunately, the above "solution" has a number of drawbacks,
including the following.

o It only supports time-based charging. The solution presented in
this document supports multiple charging metrics.

o Using accounting messages to recoup unused time may be problematic
because RADIUS accounting messages are not delivered in real-time.
A RADIUS server may store-and-forward accounting messages in
batches. Thus, relying on accounting messages for the purposes of
prepaid may cause revenue leakage. The solution presented in this
document does not rely on Accounting packets at all. It uses
Access-Request messages, which are required to flow through any
network in real-time.

o Session-Timeout(27) is not a mandatory attribute. If a prepaid
subscriber is served by a NAS that does not adhere to Session-
Timeout then that subscriber may use the service for an
undetermined period of time.

o Termination-Action(29) presents its own issues. Firstly, the
behaviour of Termination-Action(29) is not mandatory. Secondly,
according to RFC 2865, 2865 [RFC2865], Termination-Action fires when the
provision of the service has completed. However, service should
not be terminated when negotiating additional quota, because this
should happen in a manner transparent to the subscriber. Due to
the fact that Termination-Action occurs when the service is
completed, it is unclear whether or not user experience would be
affected if this attribute would be used in a prepaid scenario.
The RADIUS server might even allocate a new IP address to the
subscriber device after a Termination-Action. Also, the RADIUS
server has no way of telling why a given Access-Request message
was generated. The RADIUS server might have to wait for the
corresponding accounting packet to determine the reason. Finally, re-
authenticating
re-authenticating the subscriber may take too long. The solution
presented in this document allows quota replenishing to occur
without affecting user experience. No re-authentication is
required and quotas can be negotiated before the available credit
actually runs out.

o Due to the fact that the standard RADIUS attributes are not
mandatory, the correct prepaid operation is really an act of faith
on the part of the RADIUS server. If Session-Timeout(27) and/or
Termination-Action(29) are not supported, the prepaid subscriber
might be able to obtain the service for free. The solution
described in this document requires that a prepaid-aware SAD PPC informs the RADIUS
server, regardless of whether or not the latter supports the
prepaid extensions. The RADIUS server can then determine whether
or not service should be granted. For example, if a prepaid
subscriber is connected to a NAS that does not support prepaid,
the RADIUS server can either instruct the NAS to tunnel the
traffic to another entity in the home network (e.g. (e.g., an Home
Agent) that supports prepaid, or cause it to provide only a
restricted service.

The solution presented in this document requires the support of two
mandatory and one optional attribute. Furthermore, it does not
require a great amount of additional code at a NAS (or similar
device) that already supports time or volume volume-based metering. The
solution requires that RADIUS entities advertise their prepaid
capabilities in an Access-Request and that they generate an Access-Request Access-
Request packet with Service-
Type="Authorize-Only" Service-Type="Authorize-Only" in order to obtain
more quota when or before the current quota is used up. It also
requires the NAS to send an Access-Request with Service-Type="Authorize-Only" Service-
Type="Authorize-Only" when the session terminates in order to refund
the subscriber account.

1.3. Assumptions

This document makes the following assumptions.

o The values carried in the Service Identifiers are pre-configured
between the PPC and the PPS.

o The decision about the service rating happens at the PPS.

o The decision whether credit control requests for two services are
placed in a resource pool are made by the PPS.

o The decision which services belong to the same rating group are
pre-configured at the PPC. Once a rating group is authorized it
is not necessary to re-authorize an additional service that
belongs to the same rating group at the PPS again.

o A simple use case price enquiry is done purely for the purpose of providing AoC
for the end user, not for processing at the PPC nor to trigger any
specific actions.

1.4. Example Use Case

This section describes the sequence of events in a simple an example RADIUS
prepaid transaction.

1. When an end host attaches to a network (for example, using PPP or
PANA), IEEE
802.1X), as usual, the NAS (SAD) PPC that is servicing the subscriber uses
the AAA infrastructure in order to authenticate and authorize the
subscriber with respect to the requested service. In order to do
this, it sends a RADIUS Access-Request to the AAA server. This
Access-Request contains the subscriber's credentials and may
contain the prepaid capabilities of the SAD.
Prepaid capabilities MUST be included if the SAD supports them. PPC.

2. The authentication procedure proceeds. This may involve several
message exchanges such exchanges, as in EAP it is the case with the Extensible
Authentication Protocol (EAP) [RFC2284]. Once the subscriber has
been successfully authenticated, the home AAA server determines
that the subscriber is a prepaid subscriber and requests
authorisation from the PPS. This request MUST include the
prepaid capabilities of the serving SAD. PPC.

3. The PPS, possibly with the help of the backend infrastructure,
validates that the subscriber has a prepaid account and that the
account is active. It further validates that the SAD PPC has the
appropriate prepaid capabilities. If all is in order, the PPS
authorises the subscriber to use the network. Otherwise it
rejects the request. The decision is sent to the AAA system in
the form of a response message. In the case of success, this
message contains attributes that indicate the allocation of a
portion of the subscriber credit. This portion is called the
"initial quota" and is expressed in units of time or volume. The
response may also include a threshold value. Note that only a
portion of the user's funds is allocated because the user may be
engaged in other services that may draw on the same account. For
example, the user may be engaged in a data session and a voice
session. Although these two services would draw from the same
account, they form separate parts of the overall system. If the
entire quota was allocated to the data session then the user
would have no more funds for a voice session.

4. The AAA system incorporates the attributes received from the PPS
into an Access-Accept message that it sends to the SAD. PPC. Note
that the AAA system is responsible for authorizing the service
whereas the prepaid system is responsible for prepaid
authorization.

5. Upon receiving the Access-Response, the SAD PPC starts the prepaid
data session and meters the session based on time or volume, as
indicated in the message.

6. Once the consumption approaches the allocated limit (as expressed
by the threshold), the SAD PPC will request additional quota. Re-
authorization for additional quota flows through the AAA system
to the PPS. The PPS revalidates the subscriber account and
subtracts the previously allocated quota from the current
balance. If there is remaining balance, it reauthorizes the
request with an additional quota allotment. Otherwise, the PPS
rejects the request. Note that the replenishment of the quota is
a re-authorization procedure and does not require the subscriber
to authenticate himself again.

7. Upon receiving a re-allotment of the quota, the SAD PPC continues to
provide the data requested service until the new threshold is reached.
If the request for additional quota cannot be fulfilled then the SAD
PPC lets the subscriber use the remaining quota and terminates
the session. Alternatively, instead of terminating the session,
the
SAD PPC may restrict the data session service access in such a way that the
subscriber can only reach a particular web server. This web
server maybe used to allow the subscriber to replenish his
account. This restriction can also be used to allow new
subscribers to set up prepaid accounts in the first place.

8. Should the subscriber terminate the session before the quota is
exhausted, the remaining balance allotted to the session MUST be is
refunded into his account.

Note that the subscriber may have disconnected while the Access
Device PPC is
waiting for the initial quota. The entire allocated quota will have
to be credited back to the subscribers account in this case. Also
note that the PPS maintains session state for the subscriber. This
state includes how much account balance was allocated during the last
quota enquiry and how much is left in the account. Therefore, it is
required that all messages about the session reach the same (and
correct) PPS.

For a simple message flow, along the lines of this use case, please
see Appendix A.

2. Supported Features

This section describes the features that are supported by the
extensions specified in this document.

2.1. Multiple Concurrent Services and Quotas

Examples of services that the user may be using are browsing the web,
participating in a VoIP conversation, watching streaming video and
downloading a file. ring tone. Some operators may want to distinguish
between these services. Some services are charged and to charge them at different rates and
services may be metered
meters them differently. Therefore, the prepaid solution needs to be
able to distinguish services, and allocate quota to the services
using different unit types (time, volume) and allow for those quotas
to be consumed at different rates.

+---------+
| Session | +---------+ +-------+
| | 1
V N
+--------------+ 1 : | | M 1 +-------+ | |
| Session |<---------->| Service |------>| |<---------->| Quota |
| (service-Id) | | | | |
+---------+ +---------+ +-------+
+--------------+

Figure 4: 2: Multiple services within a single session

As shown in Figure 4, 2, a session may be associated with multiple (N)
services. Each service is identified by a service identifier
(Service-ID). The format of the Service-ID is not in the scope of
this document but it could document. It may, for example, be expressed as an IP flow using the a 5-tuple {Source-IP and Port, Destination-IP {i.e.,
source IP address, destination IP address, source port, destination
port, and Port, protocol type}. Each service is associated with a quota metric.
whereby a quota might be applicable to multiple services. An example
message flow that involves multiple such services within a single session
is given in the appendix. Appendix A.

2.2. Resource Pools

When working with multiple services a new problem arises because one
service may consume its quota faster than another service. When the
user balance is close to exhaustion, a situation could arise where
one service is unable to obtain quota while another service has
plenty of quota remaining. Unless the quotas can be rebalanced, the
SAD
PPC would then have to terminate the former service. Moreover, if each
service generates a certain amount of RADIUS prepaid traffic. In an
environment with many users and chargarble many chargeable services, this amount
of traffic is considerable may be considerable.

To avoid a situation where several parallel (and typically also
small) credit reservations must be made on the same account, and could cause undesirable network
congestion.

One method also
to circumvent avoid unnecessary load on the above situation prepaid server, it is possible to use
provide service units as a so-called "resource pool". Resource pools enable
the allocation of resources to multiple services of a session by
allocating resources to a pool and have services draw their quota
from the pool at a rate appropriate to that service. When the quota
that has been allocated to the pool is close to exhaustion, the
entire pool (rather than individual services) is replenished.

+-----------+

The reference includes a multiplier derived from the rating
parameter, which translates from service units of a specific type to
the abstract service units in the pool.

Figure 3 shows the concept of resource pools graphically.

+---------+ +---------+ +----------+
| Service-A |-----+ +--------+
+-----------+ | Ma N 1 | |
+-------->| M 1 | |
| Service |<---------->| Quota |<---------->| Resource |
| | Pool |
+-------->| (1) |
+-----------+ | Mb Pool |
+---------+ +---------+ | | Service-B |-----+ +--------+
+-----------+
+----------+

Figure 5: 3: Resource pool example

As shown in Figure 5, Service-A and Service-B are bound to Pool(1).
Ma and Mb Pools

If S is the total service units within the pool, M1, M2, ..., Mn are
the pool multipliers (that provided for services 1, 2, ..., n, and C1, C2, ...,
Cn are associated with
Service-A and Service-B respectively) that determine the rate at
which Service-A and Service-B draw from used resources within the session, then the pool.

The pool credit is initialized by taking the quota allocated to service n
exhausted and multiplying it by Mn. Therefore, re-authorization MUST be sought when:

C1*M1 + C2*M2 + ... + Cn*Mn >= S

The total credit in the amount of resources pool, S, is calculated from the quotas, which
are currently allocated to a the pool is given by Poolr as follows:

S = Ma*Qa Q1*M1 + Mb*Qb Q2*M2 + . . ., where
Qn denotes ... + Qn*Mn

For example, if the amount of quota that is allocated to rating parameter for service n.
Further, 1 is $1/MB and the pool
rating parameter for service 2 is considered to $0.1/min, the multipliers could be empty if

Poolr <= Ca*Ma + Cb*Mb + . . .,

Figure 6

where Ca
10 and Cb are resources consumed by Service-A 1 for services 1 and Service-B 2, respectively.

Note that the resources assigned to the pool are not associated with
a metric.

That is, Service-A service 1 can be rated at $1 per MB and Service-B service 2 can rated
at $0.10 per minute. In this case if $5 worth of resources are
allocated for service-A service 1 to the pool and if Ma = 10, then 50 units
would be placed into the pool. If a further $5 are allocated for
service-B
service 2 to the pool, then M=1 Mb=1 and 50 units are deposited into the
pool. The pool would then have a sum of 100 units to be shared
between the two services. The PPC would then meter the services such
that each Mbyte used by Service-A service 1 will draw 10 units from the pool
and each minute used by Service-B service 2 will draw 1 unit from the pool.

2.3. Complex Rating Functions Groups

A Rating Group gathers a set of services, identified by a service
identifier, and subject to the same cost and rating type (e.g., $0.1/
minute).

The rating of a service can be quite complex. While some operators
follow linear pricing models, others may wish to apply more complex
functions. For example, a service provider may wish to rate a
service such that the first N MBytes are free, then the next M Mbytes
are rated at $1 per MB and volume above (N+M) MB be rated at $0.50
per MB. Such a function could be implemented by repeated message
exchanges in the prepaid system.

To avert the need to exchange many messages while still supporting
such complex rating functions, the notion concept of a "Rating Group" is
introduced. A the Rating Group are typically configured at the SAD. was
introduced.

As shown in Figure 7, 6, a Rating Group is associated with one or more
services and defines the rate that the services associated with the
Rating Group consume an allocated amount of quota.

+--------------+ +--------------+
+-----------+

+---------+ +---------+ +----------+
| | N 1 | | M 1 +-------+ P 1 | | Resource Pool|
| Service-A +---------->| Service |<----->| Rating |<----->| Quota |<----->| Resource |
| | | Group |------>| or |
+-----------+ +-------+ | Pool |
+---------+ | | | Quota |
+--------------+ +--------------+
+---------+ +----------+

Figure 7: Example of a rating group 6: Rating Group

During the usage of a service that is associated with a Rating Group,
the PPC sends the ID of the Rating Group to the PPS. The PPS
authorises the Rating Group by allocating a quota to it and
optionally assigning assign it
to a Resource Pool. When an additional service that belongs to an
already authorised Rating Group is instantiated, the PPC does not
need to authorize re-authorize this service. This effectively means that the
PPC meters the service such that it draws from the already allocated
quota. Therefore, no RADIUS messages need to be exchanged in this
case. This limits the amount of traffic between the PPC and the PPS.
An example of a flow that uses Rating Groups is given in Appendix A.3

2.4. One-time Charging

One-time charging is a mode of operation of where the RADIUS prepaid
extensions are used for charging of a service that is provided
instansteneously, i.e. without an ongoing session. An example of
such an event is the purchase of a ring-tone. Subscription based
services can also be modeled as a one-time event. In this case the
one-time service event Tariff Switching

Tariff is the purchase set of a subscription.

For a given user, one-time charging may occur in parallel with other
charging models. For example, the subscriber may access a website
which is metered (based on time or volume) while he also purchases
the right to use a ring tone (a one-time-based event). Note: it is
up to the service providers to decide whether or not parameters defining the user will be
charged utilization charges for
the download use of the tone and also be charged for the time
and volume required to download the ring-tone. The facilities
provided by this document gives the service provider the capability
to achieve their service charging business goals. For example,
should the service provider choose not to charge for the download
volume or time, then they can treat the download IP flow as a
separate service that is not subject to charging.

The SAD signals one-time charging to the PPS with an indication that
identifies the service and the units that should be debited from the
user account.

A SAD may decide to perform one-time charging for an event that was
triggered by an unauthenticated user. In this case case the SAD will
have to authenticate the user before sending the relevant message to
the user's home AAA server.

Note that one-time charging can also be used to credit the prepaid
account. For example, the SAD can return resources to the subscriber
by issuing a one-time charge request that includes the amount of
resources to be credited into the account.

2.5. Tariff Switching

The PPC and the PPS may support tariff switching mechanism described
in this section. particular service.

This mechanism is useful if, for example, as shown in Figure 8, 7,
traffic before 18:00 is rated at rate r1 and traffic after 18:00 is
rated at rate r2. The mechanism requires the PPC to report usage
before and after the switch occured.

18:00
------------------+-----------------
r1 | r2
------------------+-----------------
^ ^
|<----TSI---> |
| |
Access-Accept Access-Request
(quota allocated) (quota consumed)

Figure 8: 7: Example of tariff switching Tariff Switching

The PPC it indicates support for tariff switching by setting the
appropriate bit in the PPAC. If the PPS needs to signal a tariff
switch time it will send a PTS attribute which that indicates the point in
time when the switch will occur. This indication represents the
number of seconds from current time (TariffSwitchInterval TSI).

At some point after the tariff switch the PPC sends another Access-
Request, as a result of either the user having logged off or the
volume threshold being reached. The PPC reports how much volume was
used in total (in a PPAQ attribute) and how much volume was used
after the tariff switch (in a PTS VUATS subtype attribute).

In situations with multiple tariff switches, the PPS must has to specify
the length of the tariff switch period using the
TimeIntervalAfterTariffSwitchUpdate (TITSU) field in the PTS attribute
attribute, as shown below. in Figure 8.

18:00 23:30
------------------+---------------------+--------------
r1 | r2 | r3
------------------+---------------------+--------------
^ ^ ^
|<----TSI---><-----------|-------->|TITSU
| |
Access-Accept Access-Request

Figure 9: 8: Multiple tariff switches Tariff Switches

When a TITSU is specified in the PTS, the PPC MUST generate an
Access-Request within the time after TSI and before TITSU expires.
Note that, typically, the PPC will be triggered by the Volume
Threshold. However, it is possible that, during period r2, resources
are not entirely consumed and, thus, the threshold is not reached.
The TITSU attribute ensures that, even in this case, the PPC will
generate the new Access-Request in good time.

Note that it makes no sense to use

For time based services, the tariff switching mechanism
described in this section for services that quota is continuously consumed at the
regular rate of 60 seconds per minute. At the time when credit
resources are metered based on allocated, the server already knows how many units will
be consumed before the tariff time change and how many units will be
consumed afterward. Similarly, the server can determine the units
consumed at the before rate and the units consumed at the rate
afterward in the event that the end user closes the session before
the consumption of which the allotted quota. There is no need for
additional traffic between the PPC and the PPS in the case of tariff
time changes for continuous (i.e. without
interruption). Also note that separate time based service. Therefore, the
tariff change mechanism is not used for such services. For time-
based services flows may have
individual in which the quota is not continuously consumed at a
regular rate, the tariff periods.

2.6. change mechanism described for volume and
event units may be used.

2.5. Support for Roaming

In certain networks it is essential for prepaid data services to be
available to roaming subscribers. Support for both static and
dynamic roaming models is needed. In a static roaming scenario the
subscriber connects to a foreign network which has a roaming
agreement either directly with the home network, or through a broker
network. When the subscriber logs into another foreign network, a
new login procedure has to be executed.

In a dynamic roaming scenario the subscriber may move between
networks while maintaining his connection. In such a scenario the
data session is seamlessly handed off between the networks.

In both roaming scenarios, the subscriber always authenticates
himself to the home network. Authorization for the prepaid session
and quota replenishing occurs at the home network and more
specifically at the PPS where state is being maintained.

Dynamic roaming

Roaming is challenging because a subscriber who established a prepaid
data session may move to another Access Device PPC that does not support the
prepaid extensions. Even in this case the system should
be able to continue the prepaid session.

2.7.

2.6. Dynamic Termination

When fraud or an error is detected, either only the affected session,
or all sessions of the affected subscriber should be immediately
terminated. It may further happen that the prepaid system enters a
state where it is unclear whether or not the data session is in
progress. Under certain conditions, the system may wish to
terminate the session in order to make sure that the user is not
charged for
this potential inactivity. services it does not use.

Certain handoff procedures used in dynamic roaming scenarios require
that the system terminates the subscribers prepaid data session at a
SAD.
PPC. This is the case, for example, when time-based prepaid is used
and the mobile subscriber performs a dormant handoff.

2.8. Querying

2.7. One Time Event

2.7.1. One-Time Charging

One-time charging is a mode of operation of where the RADIUS prepaid
extensions are used for charging of a service that is provided
instansteneously. An example of such an event is the purchase of a
ring tone. Subscription based services can also be modeled as a one-
time event. In this case the one-time service event is the purchase
of a subscription.

For a given user, one-time charging may occur in parallel with other
charging models. For example, the subscriber may be connected to the
Internet, which is metered (based on time or volume), while he also
purchases a ring tone (a one-time-based event).

Note that it is up to the service providers to decide whether or not
the user will be charged for the download of, for example, the video
and Rebalancing

It should also be possible charged for the PPS data volume required to Query download the current resource
consumption at a SAD
video. The facilities provided by this document gives the service
provider the capability to achieve their service charging business
goals.

The PPC signals one-time charging to the PPS with an indication that
identifies the service and adjust the units that should be debited from the
user account balance. account.

A PPC may decide to perform one-time charging and the PPC may need to
authenticate the user before sending the relevant message to the
user's home AAA server (and to the PPS).

Note that one-time charging can also be used to credit the prepaid
account. For example, a request the PPC can return resources to the PPS is made (e.g. subscriber
by issuing a one-time charging
event), request that includes the account is depleted and amount of
resources have been allocated to be credited into the account.

2.7.2. Service Price Enquiry

The PPC may need to know the price of the service event. Services
offered by application service providers whose prices are not known
in the SAD. PPC might exist. The end user might also want to get an
estimation of the price of a service event before requesting it.

A PPC issues a PPAQ to the PPS should have including the ability Requested-Action SubType
with the value set to "Price Enquiry" (2). The request includes
enough information to query identify the SAD and if service, namely a Service-
Identifier or a Rating-Group-Identifer.

The PPS calculates the cost of the requested service event, but it
has
does not perform any account balance check or credit reservation from
the spare resources account.

The estimated cost of the requested service event is returned to reassign the quotas
PPS with a PPAQ in the Cost-Information SubType. The PPC may
transfer the information to the SAD end user as an advice of charge.

More information regarding the price enquiry functionality is
provided in Section 4.2.17 and in Section 4.2.19.

2.7.3. Balance Check

The PPC may only have to verify that the
pending request. Note end user's account balance
covers the cost of a certain service without reserving any units from
the account at the time of the inquiry. This method does not
guarantee that credit would be left when the PPC requests the
debiting of the account with a separate request.

A PPC issues a PPAQ to the PPS including the Requested-Action SubType
with the value set to "Balance Check" (1). The request includes
enough information to identify the service, namely a Service-
Identifier or a Rating-Group-Identifer.

The PPS makes the balance check, but it does not know resource usage
until make any credit-
reservation from the SAD request account.

The result of balance check, namely "Success" (1) or "Failure" (2),
is returned to the PPC in the Check-Balance-Result SubType conveyed
in the PPAQ attribute from the PPS to the PPC.

More information regarding the balance check functionality is
provided in Section 4.2.17 and in Section 4.2.18.

2.7.4. Refund

Some services may refund service units to the end user's account; for more resources.
example, gaming services.

To initiate refunding the PPC includes the PPAQ attribute in an
Access-Request packet and the amount (as a negative value) to be
refunded is specified using the Resource Quota and Resource Quota
overflow subtypes. This can functionality is similar to one-time
charging with the difference that refunding uses negative values

Information about the service need to be a long time.

In provided by the absence PPC to allow
service identification, namely the Service-ID field of this capability the PPS can minimize PPAQ
identifies the effect of
this phenomenon by allocating small quotas, a practice prepaid service.

Note that results a monetary amount itself to be refunded is not provided but
rather abstract units. Based on prior out-of-band agreements between
the PPC and the PPS these abstract units are translated into a
monetary amount.

More information regarding the refund functionality is provided in more message exchanges.
Section 3.7.6.

3. Operations

This section describes contains the operations that are implemented by a
prepaid-enabled NAS (SAD). normative text for the prepaid extension.

3.1. Authentication and Authorization Operation Capability Discovery

The SAD PPC initiates the authentication and authorization procedure by
sending a RADIUS Access-Request to the HAAA. Since the SAD has PPC
capabilities, it MUST
include a PPAC attribute in the RADIUS Access-
Request. Access-Request. The PPAC
attribute indicates to the PPS which prepaid capabilities are
possessed by the SAD. PPC. These are required in order to complete the
prepaid authorization procedure. Moreover, if the
SAD supports the Disconnect-Message or the Change-of-Authorization
capabilities, then it SHOULD include the Dynamic-Capabilities
attribute.

In certain deployments, there may be other ways to terminate a data
session, or change authorization of an active session. For example,
some SADs provide a session termination service via Telnet or SNMP.
In these cases, the AAA server MAY add the Dynamic-Capabilities
message to the Access-Request. Upon receiving the Change-of-
Authorization message, the AAA server would then be responsible for
terminating the session using the means that are supported by the
device.

If the authentication procedure involves multiple message exchanges
(as in it is the case with EAP), the SAD PPC MUST include the PPAC(TBD) attribute and the
Dynamic-Capabilities PPAC attribute (if used)
in at least the last Access-
Request Access-Request of the authentication procedure.

The Access-Request is sent, as usual, to the HAAA, possibly through
one or more BAAA.

3.2. Authentication and Authorization Operation

Once the Access-Request arrives at the HAAA, the HAAA authenticates
the subscriber. If this fails, the HAAA sends an Access-Reject
message to the client. If authentication succeeds, the HAAA
determines whether or not the subscriber is a prepaid subscriber.
(How this is done is beyond the scope of this document.) If
the subscriber is not a prepaid subscriber, then the HAAA responds as
usual with an Access-Accept or an Access-Reject message. If the
subscriber is a prepaid subscriber then the HAAA SHALL MAY forward the
Access-Request to the PPS for further authorization.

The Access-Request contains the PPAC(TBD) attribute and the Dynamic-
Capabilities attribute if one was included. The User-Name(1)
attribute MAY be set to a value that identifies the subscriber. This
attribute is used by the PPS to locate his account. For added
security, the HAAA MAY also set the User-Password(2) attribute to the
password used between the HAAA and the PPS.

The PPS locates the subscriber account and authorizes him. During
this procedure, the PPS takes into consideration the SAD PPC
Capabilities. PPCs
capabilities. Upon successful authorization, the PPS generates an
Access-Accept containing an PPAC attribute and an PPAQ attribute.
The PPAC attribute returned to the client indicates the type of
prepaid service to be provided for the session. The PPAQ attribute
includes the following information.

o The QUOTA-ID, QID, which is set by the PPS to a unique value that value, is used to
correlate subsequent quota requests.

o Volume and/or Time quota, which is set to a value representing a
portion of the subscriber's credit.

o It MAY contain a Time or Volume Threshold that indicates when the
SAD PPC should
request additional quota. This information is optional.

o The IP address of the Serving serving PPS and one or more alternative
PPSs. This is used by the HAAA to route subsequent quota
replenishing messages to the appropriate PPS(s).

o A State attribute, as defined in RFC 2865. 2865 [RFC2865]. This is
necessary in order to satisfy the requirements of section Section 5.44 of
RFC 2865, 2865 [RFC2865], which mandates that an Access-Request with Service-
Type="Authorize-Only"
Service-Type="Authorize-Only" must contain a State attribute.
Since the
SAD PPC sends subsequent quota replenishment requests in the
form of such "Authorize-Only" requests, a State attribute MUST be
present in all Access-Accept messages that also carry a PPAQ
attribute.

Note: The Idle-Timeout(28) attribute can be used to trigger the
premature termination of a prepaid service, for example as a result
of inactivity.

Depending on site policies, after failed authorization, the PPS may
generate an Access-Reject in order to terminate the session
immediately. Alternatively, the PPS may generate an Access-Accept
blocking some or all of the traffic and/or redirect some or all of
the traffic to a location to a fixed server. (This feature could be
used, for example, to prompt the user to replenish their account.)
Blocking of traffic is achieved by either Filter-ID(11) or NAS-
Filter-Rule(see Redirect I-d). Redirection
Filter-Rule (see [I-D.ietf-radext-filter-rules]). A description of
the redirect functionality is achieved by sending
Redirect-Id or Redirect-Rule, HTTP Redirection defined in outside the
Redirect I-d. scope of this document.
The time period before the session is blocked/
redirected blocked/redirected is specified
by the Session-Timeout(27) attribute.

Upon receiving an Access-Accept from the PPS, the HAAA appends the
usual service attributes and forward the packet to the SAD. PPC. The HAAA
SHOULD NOT overwrite any attributes already set by the PPS. If the
HAAA receives an Access-Reject message, it will simply forward the
packet to its client. Depending on site policies, if the HAAA does
not receive an Access-Accept or an Access-Reject message from the PPS
it MAY do nothing or send an Access-Reject or an Access- Accept
message back to the PPC.

3.2.

3.3. Session Start Operation

The start of the session is indicated by the arrival of an
Accounting-Request(Start) packet. The Accounting-Request (Start) MAY
be routed to the PPS such that it can confirm the initial quota
allocation.

Note that the role of the PPS is not to record accounting messages
and therefore it SHOULD NOT respond with an Accounting Response
packet. If the PPS does not receive the Accounting-Request(start)
message it will only know that the session has started upon the first
reception of a quota replenishment operation.

If the PPS does not receive indication directly (via Accounting-
Request(start)) or indirectly, it SHOULD, after some configurable
time, deduce that the Session session has not started. If the SAD PPC supports
termination capabilities, the PPS SHOULD send a Disconnect Message to
the SAD PPC as a measure to ensure that the session is indeed dead.

3.3.

3.4. Mid-Session Operation

During the lifetime of a prepaid data session the SAD PPC may request the
replenishment of the quotas using an Authorize-Only Access-Request
message. Once either the allocated quota has been exhausted or the
threshold has been reached, the SAD PPC MUST send an Access-Request with
Service-Type(6) set to a value of "Authorize-Only" and the PPAQ
attribute.

The SAD PPC MUST also include NAS identifiers, and Session identifier Identifier
attributes in the Authorize-Only Access-Request. The Session
Identifier should be the same as the one used during the initial
Access-Request. For example, if the User-Name(1) attribute was used
in the Access-Request it MUST has to be included in the Authorize-Only
Access-Request,
Access-Request as well, especially if the User-Name(1) attribute is
used to route the Access-Request to the Home AAA server.

The Authorize-Only Access-Request MUST NOT include a User Password
and MUST NOT include a Chap CHAP Password. In order to enable the
receiver to authenticate the message, the SAD PPC MUST include a Message-
Authenticator(80). In order to satisfy the requirements of section Section
5.44 of RFC 2865, 2865 [RFC2865], the SAD PPC MUST also include the State
attribute. It is anticipated that the inclusion of the State
attribute will enable the PPS to map the Authorize-Only Access
Request to the authentication context that was established when the
PPC authenticated itself at the beginning of the session. The SAD PPC
computes the value for the Message-Authenticator and the State
attributes according to RFC 2869 [RFC2869] and RFC 2865 [RFC2865]
respectively.

When the HAAA receives an Authorize-Only Access-Request that contains
a PPAQ(TBD), PPAQ, it SHALL validate validates the message using the Message-
Authenticator(80), Message-Authenticator(80),
according to RFC 2869. If the HAAA receives an Authorize-Only
Access-Request that contains a PPAQ(TBD) PPAQ and either no or an invalid
Message-Authenticator(80) it SHALL silently discard the message. An
Authorize Only Access-Request message that does not contain a PPAQ(TBD) PPAQ is
either erroneous or belongs to another application (for example, a
Change of Authorization message [RFC3576]). In this case the
Authorize-Only Access-Request is either silently discarded or handled
by another application.

Once the Authorize-Only Access-Request message is validated, the HAAA
SHALL forward the Authorize-Only Access-Request to the appropriate
PPS. The HAAA MUST forward the Authorize-Only Access-Request to the
PPS specified in the PPAQ(TBD). PPAQ. The HAAA MUST add a Message-
Authenticator(80) to the message, according to RFC 2869. As with the
Access-Request message, the HAAA MAY modify the User-Name(1)
attribute such that it identifies the user to the PPS. Note that

When the PPS may also use the Quota-ID sub-attribute contained within the
PPAQ(TBD) to locate the user account.

Upon receiving receives the Authorize-Only Access-Request containing a
PPAQ(TBD)
PPAQ attribute, the PPS it MUST validate the Message-
Authenticator(80) Message-Authenticator(80) as
described in RFC 2869. If validation fails, the PPS MUST silently
discard the message. If it receives an Authorize-
Only Authorize-Only Access-Request
message that does not contain a PPAQ(TBD), PPAQ, it MUST silently discard the
message.

The PPS locates the prepaid session state using and uses the Quota Id QID contained
within the PPAQ(TBD). PPAQ to detect replays. The PPS takes the most recently
allocated quota and subtracts it from the user balance. If
sufficient balance remains, the PPS authorizes the PPS and allocates
additional quota. The PPS may also calculate a new threshold value.
Upon successful re-authorization, the PPS generates an Access-Accept
containing the PPAQ(TBD) PPAQ attribute. The Access-Accept message MAY
contain Servicetype(6) set to Authorize-Only and MAY contain the
Message-Authenticator(80).

Depending on site policies, upon unsuccessful authorization, the PPS
generates an Access-Reject or an Access-Accept with Filter-Id(11) or
Ascend-Data-Filter attribute (if supported) attribute and the Session-
Timeout(27) attribute such that the subscriber can get access to a
restricted set of locations for a short period of time. This feature
could be used to enable users to replenish their accounts, create new
accounts, or to browse access free content.

Upon receiving the an Access-Accept from the PPS, the HAAA SHALL return forwards the packet
message to its client. If the HAAA receives an Access-Reject
message, it forwards the packet. message. Depending on site policies, if the
HAAA does not receive an Access-Accept or an Access-Reject message
from the PPS it MAY do nothing or it MAY send an Access-Reject
message back to its client.

Upon receiving an Access-Accept, the SAD SHALL update PPC updates its quotas and
threshold parameters with the values contained in the PPAQ(TBD) PPAQ attribute.
Note that the PPS MAY update the PrePaidServer attribute(s) and these
may have to be saved as well. If the Access-
Accept Access-Accept message contains
a Filter-Id(11), an Ascend-Data-Filter attribute, or Session
Timeout(27), the SAD PPC SHALL restrict the subscriber session
accordingly.

3.4.

3.5. Dynamic Operations

The PPS may take advantage of the dynamic capabilities that are
supported by the SAD PPC as advertised in the Dynamic-Capabilities
attribute during the initial Access-Request. There are two types of
action
actions that the PPS may perform. Firstly, it may request the
session to be terminated. Secondly, it may request the attributes
associated with the session to be modified. More specifically, it
may modify a previously sent PPAQ(TBD). PPAQ.

Both of these actions require that the session be uniquely identified
at the SAD. As a minimum, the PPS MUST provide

1. either the NAS-IP-Address(4) or the NAS-Identifier(32), and

2. at least one session identifier such PPC as User-Name(1), Framed-IP-
Address(), the Accounting-Session-Id(44).

Other attributes could also be used to uniquely identify a prepaid
data session.

3.4.1. described in [RFC3576].

3.5.1. Unsolicited Session Termination Operation

At anytime during a session the PPS may send a Disconnect Message in
order to terminate a session. This capability is described in detail session, see in [RFC3576]. The PPS sends a Disconnect Message that MUST contain
identifiers that uniquely identify the data session and the SAD
servicing that session.

If the SAD receives a Disconnect-Message, it responds with either a
Disconnect-ACK message (if it is able to terminate the session) or
with a Disconnect-NAK packet (otherwise). Upon successful
termination of a session the SAD PPC MUST return any unused quota to the
PPS by issuing an Authorize-Only Access-Request containing the PPAQ
which contains any unused Quota quota and the Update-Reason set to "Remote
Forced Disconnection".

3.4.2.

3.5.2. Unsolicited Change of Authorization Operation

At any time during the session the PPC may receive a Change of
Authorization (CoA) message. A PPS may send a new Quota quota to either
add or to remove quota that is allocated to the service. If the
Change of Authorization contains a PPAQ then that PPAQ overrides a
previously received PPAQ. The PPS MUST NOT change the units used in
the PPAQ.

If the newly received PPAQ reduces the amount of allocated quota
beyond what is already used then the SAD PPC accepts the new PPAQ and act
as it normally would when the quota is used up. For example, if the
threshold is reached then is request a quota update .

3.5. update.

3.6. Termination Operation

The termination phase is initiated when (i) the subscriber logs off,
(ii) the subscriber balance is exhausted, or (iii) when the SAD PPC
receives a Disconnect Message.

In case the user logged off, or the SAD PPC receives a Disconnect
Message, the SAD PPC sends an Authorize-Only Access-Request message with
a PPAQ and Update-Reason attribute set to either "Client Service
Termination" or "Remote Forced Disconnect". This message indicates
the amount of consumed quota.

In case the currently allocated quota is exhausted, if the PPAQ
contained the Termination-Action field, the SAD follows the specified
action (which would be to immediately terminate the service, request
more quota, or redirect/filter the service).

3.6. Mobile IP Operations

In roaming scenarios with Mobile-IP, the prepaid data session should
be maintained transparently if the HA is acting as subytype, the SAD. As the
subscriber device associates with a new SAD (AP or PDSN that supports PPC capability), the SAD sends a RADIUS Access-Request and the
subscriber is re-authenticated and reauthorized. The SAD MUST
include the PPAC(TBD) attribute in the RADIUS Access-Request. In
this manner, the procedure follows the Authentication and
Authorization procedure described earlier.

If the HA was acting as the SAD before handoff, the prepaid session
does not undergo any change after the handoff because the Mobile IP
session is anchored at the HA and the user's Home IP address does not
change.

In the case of a wireless access point or PDSN acting as the SAD, it
is likely that the user's (care-of) IP address will change. The
prepaid session will be affected by this. In this scenario the SAD
shall send an Access-Request message which is routed to the home
network and MUST reach the PPS that is serving this session. The PPS
correlates the new authorization request with the existing active
session and assigns a quota to the new request. Any outstanding
quota at the old SAD MUST be returned to the PPS if the Mobile-IP
nodes (HA and FA) support registration revocation (Mobile IPv4 only).
Specifically, the quota SHOULD be returned when the SAD sends the
Authorize-Only Access-Request with PPAQ(TBD) Update-Reason set to
either "Remote Forced Disconnect" or "Client Service Termination".
In order to trigger the sending of this last Authorize-Only Access-
Request, the PPS may issue a Disconnect Message [3576] to the SAD.

Even if the subscriber moves to a SAD that does not have prepaid
capabilities can the prepaid data service continue. This can be done
by requesting the Home Agent (assuming it has such capabilities) to
take over the responsibilities of the SAD (i.e. metering). This
scenario will be discussed in detail in a later version of this
document.
specified action.

3.7. Operation Considerations for Multiple Services

This section describes the support for multiple prepaid services on a
single SAD. PPC. Message flows illustrating the various interactions are
presented in Appendix A.

A SAD PPC that supports prepaid operations for multi-services SHOULD set
the "Multi-Services Supported" bit in the PPAC. When working with
multi-services, we need to differentiate between the services. A
Service-Id attribute is used in the PPAQ(TBD) PPAQ in order to uniquely
differentiate between the services. The exact definition of the
Service-Id attribute is outside the scope of this document.

A PPAQ that contains a Service-Id is associated with that Service. service. A
PPAQ that contains a Rating-Group-Id is associated with that Rating-
Group. A PPAQ MUST not NOT contain both a Rating-Group-Id and a
Service-Id. A PPAQ that contains neither a Rating-Group-Id or nor a
Service-Id applies to then the Access Service. default service is used, i.e., the "Access
Service".

3.7.1. Initial Quota Request

When operations with multi-services multiple services is desired, desired then the SAD PPC
requests the initial quota for the Service by sending a PPAQ containing the
Service-Id for that Service in an Authorize-Only Access-Request
packet. packet for that
service. Similarly, if the SAD PPC supports Rating-Groups rating groups then it may
request a quota for the Rating-Group rating group by sending a PPAQ containing the
Rating-Group-Id. In both cases the Update-Reason is set to "Initial-
Request". The Authorize-Only Access-Request message may MAY contain more
than one PPAQ. The Authorize-Only Access-Request MUST include one or more
attributes that serve to identify the session so that it can be
linked to the original authentication. Which Session Identifiers are
included is up to specific deployments. The Authorize-Only message
must contain the Message-Authenticator(80) attribute for integrity
protection of the Authorize-Only Access-Request message.

Upon receiving an Authorize-Only Access-Accept message containing one
or more PPAQs, the PPS allocates resources to each PPAQ. Each PPAQ
is assigned a unique QID that MUST appear in subsequent PPAQ updates
for that service or rating-group. rating group. Additionally, the PPAQ MUST
contain the Service-ID or Group-ID, Rating-Group-Id, unless the PPAQ is the
generic "Access Service".

3.7.2. Quota Update

Once the services start to utilize their allotted quota they will
eventually need to replenish their quotas (either the threshold is
reached or no more quota remains). In order to replenish the quota,
the PPC sends an Authorize-Only Access-Request message containing one
or more PPAQs. Each PPAQ MUST contain the appropriate QID,
Service-ID or Group-ID Rating-Group-Id (or neither the Service-ID or Rating-
Group-Id if the quota replenishment is for the "Access Service").
The Update-Reason filed indicates either "Threshold reached"(3), or
"Quota reached"(4).
The Authorize-Only message must contain session identifiers.

Upon receiving an Authorize-Only Access-Request packet with one or
more PPAQs the PPS responds with a new PPAQ for that service. The
PPAQ contains a new QID, the Service-Id or the Rating-Group-Id, and a
new
Quota. QID. If the PPS does not grant additional quota to for the service
it MUST include the Termination-Action subfield in the PPAQ that will
instruct the SAD what PPC to do with the service. take appropriate actions.

3.7.3. Termination

When the allotted quota for a service is exhausted, the SAD PPC shall act
in accordance with the Termination-Action field flags set in the Quota. Termination-Action subtype.
If the Termination-Action field subtype is absent then the service MUST be
terminated. If the service is to be terminated, then the SAD PPC shall
send a PPAQ with the appropriate QID, the Service-Id, the used quota,
and the Update-Reason set to "Client Service Termination".

If the oAccess Serviceoe "Access Service" has terminated, then all other services must
be terminated as well. In this case the SAD PPC MUST report on all
issued quotas for the various services. The Update-Reason field
should be set to "Access Service Terminated".

3.7.4. Dynamic Operations

Dynamic operations for multi-services are similar to dynamic
operations described for single service operations. The prepaid
system may PPS MAY send
a COA message containing a PPAQ for an existing service instance.
The SAD PPC matches the PPAQ with the service using the Service-ID or the
Rating-Group-Id attribute. The new quota could differ from the
previously allocated value. The SAD must react to the new value
accordingly.

A disconnect message terminates the "Access Service". As such the
SAD
PPC MUST report all unused quotas by sending an Authorize-Only Access
Request message containing a PPAQ for each active service. The
Update-Reason shall MAY indicate that the reason for the update.

3.7.5. Support for Resource Pools

If the PPC supports pools as indicated by setting the "Pools
supported" bit in the PPAC(TBD) PPAC then the PPS may associate a Quota quota with a
Pool by including the Pool-Id and the Pool-Multiplier in the
PPAQ(TBD). PPAQ.
When Resource Pools are used, the PPAQ must not MUST NOT use the threshold
field.

3.7.6. One-time Charging

To initiate a One-Time charge one-time charging the PPC includes the PPAQ attribute in
an Access-Request packet. The Access Request packet MUST include a
Message-Authenticator(80) and an Event-Timestamp(55) attribute. The
Service Id Service-ID field of the PPAQ
identifies the prepaid service. The amount to be charged is
specified using the Resource Quota and Resource Quota overflow
subtypes. If the value specified is negative then the resources are
credited to the user account. This functionality corresponds to
refunding.

The QID field subtype MUST be set to a unique value and is used by the PPS
to detect duplicates. The Update Reason field MUST be set to One-Time One-
Time Charging. Upon receiving a One-Time charge PPAQ, the RADIUS
server authenticates the user and, if successful, passes the PPAQ to
the PPS. The PPS locates the account and debits or credits it
accordingly. The PPS MUST respond to the PPS with an Access-Accept
message if successful, or an Access-Reject message otherwise.

The RADIUS server shall respond

In case of a successful operation the HAAA forwards the message to
the SAD PPC with an Access Accept message. Since this is a one-time
charge the SAD must not PPC MUST NOT allow the session to continue. Therefore,
the RADIUS server should SHOULD include in the Access-Accept a Session-Timeout Session-
Timeout set to 0. Upon receiving an Access-Accept response the SAD shall PPC
SHOULD generate an Accounting Stop message.

A PPAQ used for One-Time charging may MAY appear in an Authorize-Only
Access Request. This is the case when the session already exists.
The PPS responds with an Access-Accept to indicate that the user
account has been debited or an Access-Reject otherwise.

3.7.7. Error Handling

If the PPS receives a PPAQ with an invalid QID it MUST ignore that
PPAQ.

If the PPS receives a PPAQ containing a Service-Id, or a Rating-
Group-Id that it does not recognize, then it MUST ignore that PPAQ.

If the PPC receives a PPAQ containing a Service-Id, or a Rating-
Group-Id that it does not recognize, then it must MUST ignore that PPAQ.

If the PPC receives a PPAQ that contains a Pool-Id without a Pool-
Multiplier or a Pool-Multiplier without a Pool-Id it must MUST ignore that
PPAQ.

3.7.8. Accounting Considerations

Although typically generated, accounting messages are not required to
deliver a prepaid data service. When generated, accounting messages
are used for auditing purposes and for billing. Accounting messages
associated with prepaid data sessions should include the PPAQ(TBD) PPAQ
attribute.

3.7.9. Interoperability with Diameter Credit Control Application

The RADIUS prepaid extensions need to interoperate with the Diameter
protocol. Two interoperability scenarios exist, as follows. Either
the AAA infrastructure is Diameter based and the SAD are RADIUS
based, or the SAD is Diameter based and the AAA infrastructure is
RADIUS based.

The Diameter Credit Control Application [DIAMETERCC] describes how to
implement a prepaid accounting system using a Diameter based
infrastructure.

4. Attributes

This section specifies the attributes that implement the RADIUS
extensions for prepaid. Their general format follow that of the base
RADIUS [RFC2865] and take also account current design guidelines that
are proposed in the RADEXT working group. The type field of these
attributes contains a value that is drawn from the type value space
specified in [RFC2865]. The exact value for the type field of each
attribute is to be allocated by IANA. Note that, unless otherwise
specified, the format of the value field of each of the AVPs defined
in this section adheres to one of the formats specified in section 5
of [RFC2865]. In particular, the labels "string", "integer", and
"address" are used to indicate the format in the remainder of this
document.

4.1. PPAC PrePaid Accounting Capability (PPAC) Attribute

The PrepaidAccountingCapability (PPAC) attribute is sent in the
Access-Request message by a prepaid capable NAS and is used PPC to describe the its prepaid capabilities of the NAS. The PPAC is also
present in an Access-Accept message by the PPS in order to indicate
the type of metering that is to be applied to this session. capabilities.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TYPE | LENGTH | SUBtype 1 SubType (1) | LENGTH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AvailableInClient (AiC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AvailableInClient-Extended (AiC-ext) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

TYPE : IANA registered value of PPAC attribute
LENGTH: 8
VALUE : Data type String

The value MUST be field is encoded as follows:

Subtype (=1)

SubType : Subtype for AvailableInClient attribute Value (1)
Length : Length of AvailableInClient attribute
(= 6 octets) or 10 octets

AvailableInClient (AiC): The optional AvailableInClient Subtype, generated by the PPC,
indicates the metering capabilities of the NAS and shall be bitmap
encoded. The possible values are as follows.

0x00000001 is encoded as:

Value | Description
-------------+-------------------------------------
00000001 | Volume metering supported.
0x00000002 supported
00000010 | Duration metering supported.
0x00000004 supported
00000100 | Resource metering supported.
0x00000008 supported
00001000 | Pools supported
0x00000010
00010000 | Rating groups supported
0x00000020
00100000 | Multi-Services supported.
0x00000040 supported
01000000 | Tariff Switch supported.

Others Reserved

Figure 10: PPAC Attribute

4.2. Session Termination Attribute

The value supported
10000000 | Extended AiC field

If the Extended AiC flag is bitmap encoded. This attribute not set then the length
of this SubType is included in a RADIUS
Access-Request message to 6 octets. If the RADIUS server Extended AiC flag
is, however, set then the length of this SubType is
10 octects long and indicates whether or
not the NAS supports Dynamic Authorization.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 subsequent 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ octects are
available as shown below:

AvailableInClient-Extended (AiC-ext):

The bitmap is encoded as:

Value | TYPE Description
-------------+-------------------------------------
00000001 | LENGTH **Available via IANA registration**
00000010 | String **Available via IANA registration**
00000100 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type : value of Session Termination Capability
Length: = 4
String encoded as follows:

0x00000001 Dynamic Authorization Extensions (rfc3576) is
supported. **Available via IANA registration**
00001000 | **Available via IANA registration**
00010000 | **Available via IANA registration**
00100000 | **Available via IANA registration**
01000000 | **Available via IANA registration**
10000000 | **Available via IANA registration**

Figure 11: Session Termination 9: PPAC Attribute

4.3. PPAQ

4.2. Prepaid Accounting Operation (PPAQ) Attribute

One or more PPAQ attributes are sent in an Access Request, Authorize-
Only Access-Request and Access-Accept message. In an Access Request
message, the PPAQ attribute is used to facilitate One-Time one-time charging
transactions. In Authorize-Only Access-Request messages it is used
for One-Time one-time charging, report usage and the to request for further quota. It
is also used in order to request prepaid quota for a new service
instance. In an Access-Accept message it is used in order to
allocate the (initial and subsequent) quotas.

When multiple services are supported, a PPAQ is associated with a
specific service as indicated by the presence of a Service-Id, a
Rating-Group-Id, or the "Access Service" (as indicated by the absence
of both, the Service-Id and the Rating-Group-Id).

Either Volume-Quota, Time-Quota, or Resource-Quota SubTypes MUST
appear in the PPAQ attribute, except for the price enquiry message
exchange where these subtypes MUST be absent. A single PPAQ
attribute MUST NOT contain more than one Service-Id, MUST NOT contain
more than one Rating-Group-Id, and MUST NOT contain both a Service-Id
and a Rating-Group-Id). Rating-Group-Id. A PPAQ that does not contain a Service-ID or
a Rating-Group-Id refers to the "Access Service". A PPAQ MUST NOT
contain more than one Pool-Id. A PPAQ that contains a Pool-Id MUST
also contain a Pool-Multiplier SubType.

The attribute PPAQ attribute, as shown in Figure 10, has a variable length
(greater than 8, encoded into one octet), and consists of a variable
number of subtypes. Unused subtypes are omitted from the message.
In the following subsections the various subtypes of the PPAQ
attribute are specified.

4.3.1.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TYPE | LENGTH | VALUE ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... VALUE |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

TYPE : value of PPAQ
LENGTH: variable
VALUE : Data type String

Each subattribute is then encoding in the following style:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SubType | LENGTH | VALUE ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 10: PPAQ Attribute

4.2.1. Quota Identifier AVP (QID) SubType

The value of the type field of the QuotaIDentifier AVP Quota Identifier (QID) SubType is
TBD. The length of this AVP SubType is 6 octets. Its value is encoded
as a string. It is generated by the PPS together with the allocation of new quota.
The online quota update RADIUS Access-Request message that is sent and subsequently returned in
a PPAQ->QID subtype from the SAD PPC to the PPS includes PPS. This field has the
semantic of a previously received
QuotaIdentifier AVP.

4.3.2. transaction identifier and therefore changes with every
transaction initiated by the PPS to the PPC.

4.2.2. VolumeQuota AVP SubType

The value of the type field of the VolumeQuota AVP SubType is TBD. The
length of this AVP SubType is 12 or 18 octets. The AVP It is only present if
volume-based charging is used. In a RADIUS Access-Accept message
(PPS to SAD PPC direction), it indicates the volume (in octets) allocated
for the session by the PPS. In an RADIUS Authorize-Only Access-
Request message (SAD (PPC to PPS direction), it indicates the total used
volume (in octets) for both inbound and outbound traffic. The
attribute consists of a Value-Digits AVP SubType and optionally an
Exponent
AVP SubType (as indicated in the length field). The Exponent AVP,
SubType, if present, MUST NOT encode a negative number or zero.

4.3.3.

4.2.3. VolumeThreshold AVP SubType

The value of the type field of the VolumeThreshold AVP SubType is TBD and
its length is 12 or 18 octets. This AVP SubType is optionally present if
VolumeQuota is present in a RADIUS Access-Accept message (PPS to SAD PPC
direction). It is generated by the PPS and indicates the volume (in
octets) that shall has to be consumed before a new quota should be is requested.
This threshold should not MUST NOT be larger than the VolumeQuota. The
attribute consists of a Value-Digits AVP SubType and optionally an
Exponent AVP SubType (as indicated by the length field). The Exponent AVP,
SubType, if present, MUST NOT encode a negative number or zero.

4.3.4.

4.2.4. DurationQuota AVP SubType

The value of the type field of the DurationQuota AVP SubType is TBD and
its length is 6 octets. This optional AVP SubType is only present if duration-
based
duration-based charging is used. In a RADIUS Access-Accept message
(PPS to SAD PPC direction), it indicates the duration (in seconds)
allocated for the session by the PPS. It is encoded as an integer.
In an on-line a RADIUS Access-Accept Access-Request message (PPC to PPS direction), it
indicates the total duration (in seconds) since the start of the
accounting session related to the QuotaID QID subtype of the PPAQ AVP attribute
in which it occurs.

4.3.5.

4.2.5. DurationThreshold AVP SubType

The value of the type field of the DurationThreshold AVP SubType is TBD
and its length is 6 octets. This AVP SubType shall optionally be present
if the DurationQuota is present in a RADIUS Access-Accept message
(PPS to PPC direction). It represents the duration (in seconds)
after which new quota should be requested. This threshold should not MUST NOT
be larger than the DurationQuota. DurationQuota SubType. It is encoded as an
integer.

4.3.6.

4.2.6. ResourceQuota AVP SubType

The value of the type field of the ResourceQuota AVP SubType is TBD. The
length of this AVP SubType is 12 or 18 octets. This optional AVP SubType is
only present if resource-based or one-time charging is used. In the
RADIUS Access-Accept message (PPS to SAD PPC direction) it indicates the
resources allocated for the session by the PPS. In RADIUS Authorize-
Only Access-Request message (SAD (PPC to PPS direction), it indicates the
resources used in total, including both incoming and outgoing
chargeable traffic. In one-time charging scenarios, the subtype
represents the number of units to charge or credit the user. The
attribute consists of a Value-Digits AVP SubType and optionally an
Exponent
AVP SubType (as indicated by the length field).

4.3.7.

4.2.7. ResourceThreshold AVP SubType

The value of the type field of the ResourceThreshold AVP SubType is TBD.
The length of this AVP SubType is 12 or 18 octets. The semantics of this AVP
SubType follow those of the VolumeThreshold and DurationThreshold AVPs.
SubType. It consists of a Value-Digits AVP SubType and optionally an
Exponent AVP.

4.3.8. SubType.

4.2.8. Value-Digits AVP SubType

The value of the type field of the Value-Digits AVP SubType is TBD and
its length is 10 octets. This AVP SubType encodes the most significant
digits of a number, encoded as an integer. If decimal values are
needed to present the number, the scaling MUST be indicated with a
related Exponent AVP. SubType. For example, the decimal number 0.05 is
encoded by a Value-Digits AVP SubType set to 5, and a scaling that is
indicated with the Exponent AVP SubType set to -2.

4.3.9.

4.2.9. Exponent AVP SubType

The value of the type field of the Exponent AVP SubType is TBD. The
length of this AVP SubType is 6 octets. This AVP SubType contains the
exponent value that is to be applied to the accompanying Value-Digit AVP.
SubType. Its value is encoded as an integer.

4.3.10.

4.2.10. Update-Reason AVP SubType

The value of the type field of the Update-Reason AVP SubType is TBD. The
length of this AVP SubType is 4 octets. This AVP shall be SubType is present in the on-
line a
RADIUS Access-Request message (PPC to PPS direction). It direction) and indicates
the reason for initiating the on-line quota update operation. Update reasons 6, 7, 8
(6), (7), (8) and 9 (9) indicate that the associated resources are
released at the client PPC side, and that therefore the PPS
shall not MUST NOT
allocate a new quota in the RADIUS Access Accept message.

The following values for the Update-Reason SubType are defined:

Value | Description
-------------+--------------------------------------
0 | Reserved
1 | Pre-initialization
2.
2 | Initial Request

3.
3 | Threshold Reached

4.
4 | Quota Reached

5.
5 | TITSU Approaching

6.
6 | Remote Forced Disconnect

7.
7 | Client Service Termination

8.
8 | "Access Service" Terminated

9.
9 | Service not established

10.
10 | One-Time Charging

4.3.11.
11..255 | **Available for IANA registration**

Figure 11: Values for Update-Reason SubType

4.2.11. PrepaidServer AVP SubType

The value of the type field of the PrepaidServer AVP SubType is TBD. The
length of this AVP SubType is 6 or 18 octets, for IPv4 and IPv6 addresses
respectively. This optional AVP SubType indicates the address of the
serving PPS. If present, the Home RADIUS server uses this address to
route the message to the serving PPS. The attribute may be sent by the
Home RADIUS server. Multiple instances of this
subtype MAY be present in a single PPAQ AVP. attribute. The value of this AVP
SubType is encoded as an address.

If present in the PrepaidServer SubType of an incoming RADIUS Access-Accept Access-
Accept message, the SAD
shall send PPC returns this attribute SubType back without modifying
it in the subsequent RADIUS Access-Request message, except for the first one. message. If multiple
values are present, the SAD shall not PPC MUST NOT change their order.

4.3.12.

4.2.12. Service-ID AVP SubType

The value of the type and length fields of the Service-ID AVP SubType are
TBD. The value field of this AVP SubType is encoded as a string. This
value is handled as an opaque string that uniquely describes the
service instance to which prepaid metering should be applied.

A Service-Id could be an IP 5-tuple (source address, source port,
destination address, destination port, protocol). If a Service-ID AVP
SubType is present in the PPAQ, the entire PPAQ attribute refers to
that service. If a PPAQ attribute does not contain a Service-Id or
Rating-Group-ID, then the PPAQ attribute refers to the Access Service.

4.3.13. "Access
Service".

4.2.13. Rating-Group-ID AVP SubType

The value of the type field of the Rating-Group-ID SubType is TBD.
The length of this AVP SubType is 6 octets. This AVP SubType indicates that
this PPAQ attribute is associated with resources allocated to a
Rating Group with the corresponding ID. This AVP SubType is encoded as a
string. A single PPAQ MUST NOT contain more than one
Rating-Group-ID.

4.3.14.

4.2.14. Termination-Action AVP SubType

The value of the type field of the Termination-Action AVP SubType is TBD.
The length of this AVP SubType is 3 octets. This AVP SubType contains an
enumeration of the action to take when the PPS does not grant
additional quota. Valid actions are as follows. (Note that

The following values for the value Termination-Action SubType are defined:

Value | Description
-------------+------------------------------------
0 is reserved.)

1. | Reserved
1 | Terminate

2.
2 | Request More Quota

3.
3 | Redirect/Filter

4.3.15.
4..255 | **Available for IANA registration**

Figure 12: Values for the Termination-Action SubType

4.2.15. Pool-ID AVP SubType

The value of the type field of the Pool-ID AVP SubType is TBD. The
length of this AVP SubType is 6 octets. This AVP octets and it identifies the resource pool that the
quota included in this PPAQ is associated with.
pool. It is encoded as a string.

4.3.16.

4.2.16. Pool-Multiplier AVP SubType

The value of the type field of the Pool-Multiplier AVP SubType is TBD.
The length of this AVP SubType is 12 or 18 octets. The pool-multiplier pool multiplier
determines the weight that resources are inserted into the pool that
is identified by the accompanying Pool-ID AVP, SubType, and the rate at
which resources are taken out of the pool by the relevant Service or
Rating-Group. The attribute SubType consists of a Value-Digits AVP SubType and
optionally an Exponent AVP SubType (as indicated by the length field).

4.3.17.

4.2.17. Requested-Action AVP SubType

The value of the type field of the Requested-Action AVP SubType is TBD.
The length of this AVP SubType is 3 octets. This AVP can octets and it is only be present in
messages sent from the PPC to the PPS. It indicates that the user or
the PPC
desires the PPS to perform the indicated action and to return the
result. The PPAQ in which a Requested-Action AVP SubType occurs MUST NOT
contain a QID, and MUST contain a Service-Identifier that, possibly
in combination with other AVPS, can be used by or a Rating-
Group-Identifer that allows the PPS to uniquely identify the service
for which the indicated action is requested.

The following actions may be requested.

1. values for the Requested-Action SubType are defined:

Value | Description
-------------+-------------------------------------
0 | Reserved
1 | Balance Check

2.
2 | Price Enquiry

4.3.18.
3..255 | **Available for IANA registration**

Figure 13: Values for the Requested-Action SubType

4.2.18. Check-Balance-Result AVP SubType

The value of the type field of the Check-Balance-Result AVP SubType is
TBD. The length of this AVP SubType is 3 octets. This AVP SubType can only
be present in messages sent from the PPS to the PPC. It indicates
the balance check decision of the PPS about a previously received
Balance Check Request (as indicated in a Requested-Action AVP). Possible values
are 0 for "success" and any other value for "failure" and mean that
sufficient funds are available (resp. are not available) in the
user's prepaid account. SubType).
The PPAQ attribute in which a Check-Balance-Result occurs MUST NOT
include a QID, because no quota is reserved by QID.

The following values for the
PPS.

4.3.19. Check-Balance-Result SubType are
defined:

Figure 14: Values for the Check-Balance-Result SubType

4.2.19. Cost-Information AVP SubType

The value of the type field of the Cost-Information AVP SubType is TBD.
The length of this AVP SubType is variable. This AVP SubType is used in
order to return the cost information of a service, which the PPC can
transfer transparently to the end user. This AVP SubType is sent from
the PPS to the PPC as a response to a "Price Enquiry", as indicated
by the Requested-Action AVP. SubType. This AVP SubType consists of four
further AVPs, SubTypes, as
follows.

1. follows:

Value-Digits ASP: this SubType:

The Value-Digits SubType encodes the most significant digits of
the monetery value that represents the cost in question.

Exponent AVP: this SubType:

The Exponent SubType encodes the exponent that applies to the
Value-Digits AVP.

3. SubType.

Currency-Code AVP: SubType:

the value of the type field of this AVP SubType is TBD. The length of
this AVP SubType is 4 octets. It encodes the currency code, as
defined in the ISO 4217 standard.

Cost-Unit AVP: SubType:

the value of the type field of this AVP SubType is TBD. The length of
this AVP SubType is variable. It carries a UTF8String encoded human
readable string that can be displayed to the end user. It
specifies the applicable unit to the Cost-Information when the
service cost is a cost per unit (e.g., cost of the service is $1
per minute). The Cost-Unit can be minutes, hours, days,
kilobytes, megabytes, etc.

Example:

For example, the cost of 7.75 Malawi kwacha per hour would be encoded
as follows. Value-Digits = 775, Exponent = -2, Currency Code = 103,
and Cost-Unit = "hour".

The PPAQ in which that carries a Cost-Information occurs MUST NOT include a QID,
because no quota is actually reserved by the PPS.

NOTES: Either Volume-Quota, Time-Quota, or Resource-Quota MUST appear
in the PPAQ attribute. A PPAQ MUST NOT contain more than one
Service-Id, MUST NOT contain more than one Rating-Group-Id, and MUST
NOT contain both a Service-Id and a Rating-Group-Id. A PPAQ that
does not contain a Service-ID or a Rating-Group-Id refers to the
"Access Service". A PPAQ MUST NOT contain more than one Pool-Id. A
PPAQ that contains a Pool-Id MUST also contain a Pool-Multiplier AVP.

4.4. QID.

4.3. Prepaid Tariff Switching Attribute (PTS) Attribute

This specification defines the PTS attribute attribute, which allows for
changeovers to switch
from one rate to another during service provision. Support for
tariff switching is optional to implement and to use for both the PPC and
the PPS. PPCs use the flag "Tariff Switching supported" of in the
AvailableInClient subtype field of the PPAC attribute in order to indicate
support for tariff switching. PPSs employ the PTS attribute in order
to announce their support for tariff switching. Details of this will
be specified after the format of the PTS attribute has been defined.

If a RADIUS message contains a PTS attribute, it MUST also contain at
least one PPAQ attribute. If a RADIUS Access-Request message
contains a PTS attribute or a the "Tariff Switching supported" flag, flag in
the AvailableInClient field of the PPAC attribute, it MUST also
contain an Event-Timestamp RADIUS attribute (see [RFC2869]).

The value of the type field of the PTS AVP is TBD. The length of
this AVP is variable. It contains one or more subtypes, as follows.

Every PTS AVP attribute MUST include a QuotaIdentifier AVP QID SubType, as specified in
Section 4.3.1. 4.2.1. In an online a RADIUS Access-Request message sent from the PPC
to the PPS, the QuotaIdentifier AVP must QID SubType MUST contain a quota
identifier the value of the Quota
Identifier SubType that was previously received from the PPS and MUST
be the same as a quota identifier the value carried in the QID SubType of one of the
PPAQ attributes included the same RADIUS message.

If multiple services are supported and if the PPAQ is associated with
a service as indicated by the Service-ID SubType, then the PTS refers
to the tariff switch for that service. If the PPAQ does not have a
Service-ID, then the PTS refers to tariff switch for the "Access
Service".

A PPAQ attribute that is transported along with a PTS attribute and
has the same quota identifier value as the QID SubType contained in the PTS attribute
in its own QID subfield SubType is referred to as the "accompanying PPAQ
attribute". If a PPS receives an Access-Request message from a PPC,
it associates a unique quota identifier value for the QID SubType to this request. Thus, a quota identifier
also identifies a particular service.

The PTS AVP attribute, as shown in Figure 15, contains a number of other subtype AVPs
subtypes which are specified in the following subsections.

4.4.1.

TYPE : value of PTS
LENGTH: variable
VALUE : Variable length content of data type String

Each SubType is then encoding in the following style:

Figure 15: PTS Attribute

4.3.1. VolumeUsedAfterTariffSwitch AVP SubType

The value of the type field of the VolumeUsedAfterTariffSwitch AVP
(VUATS) SubType is TBD. The length of this AVP SubType is 12 or 18
octets. The VolumeUsedAfterTariffSwitch subtype SHALL SHOULD be used in online
the RADIUS Access-Request messages (PPC to PPS direction). It
indicates the volume (in octets) used during a session after the last
tariff switch for the service specified via the QID subfield SubType and the
accompanying PPAQ attribute. The attribute consists of a Value-Digits AVP Value-
Digits SubType and optionally an Exponent AVP SubType (as indicated in
the length field).

4.4.2.

4.3.2. TariffSwitchInterval AVP SubType

The type of the TariffSwitchInterval (TSI) SubType is TBD and its
length 6 octets. This AVP SubType MUST be present in each PTS attribute
that is part of a RADIUS Access-Accept message (PPS to PPC
direction). It indicates the interval (in seconds) between the value
of Event-Timestamp RADIUS attribute (see [RFC2869]) of the
corresponding RADIUS Access-Request message and the next tariff
switch condition.

4.4.3.

4.3.3. TimeIntervalafterTariffSwitchUpdate AVP SubType

The value of the type field of the
TimeIntervalafterTariffSwitchUpdate (TITSU) AVP SubType is TBD. The
length of this AVP SubType is 6 octets. The PPS MUST include this AVP
SubType if there is another tariff switch period after the period
that ends as indicated by the TSI attribute. SubType. The value of the TITSU AVP
SubType in encoded as an integer, and contains the number of seconds
of the tariff period that begins immediately after the period that
ends as indicated by the TSI attribute. If the TITSU attribute SubType is not
present, the PPC assumes that the tariff period which ends as
indicated by the TSI attribute SubType lasts until further notice. If TITSU is
specified, the PPC MUST send a quota update before the point in time
specified by the TITSU
attribute SubType (see Figure 9).

If a 8).

5. Diameter RADIUS message contains a PTS attribute, it MUST also contain at
least one PPAQ attribute. Interoperability

The PTS is associated RADIUS prepaid extensions need to interoperate with the PPAQ by the
QID. If multiple services are supported and if the PPAQ is
associated with a service Diameter
protocol. Two interoperability scenarios exist, as indicated by the Service-ID AVP, then
the PTS refers to the tariff switch for that service. If the PPAQ
does not have a Service-ID, then follows. Either
the PTS refers to tariff switch for AAA infrastructure is Diameter based and the Access-Service.

If a PPC supports tariff switching then it MUST set the 0x00000040
(Tariff switching supported) flag of the AvailableInClient subtype of are RADIUS
based, or the PPAC attribute that PPC is contained in the Access-Request packet
starting the session.

5. Translation between RADIUS prepaid and Diameter Credit Control

In scenarios where the service metering device uses the "RADIUS
prepaid" (RPP) protocol for accounting based and prepaid charging while the AAA infrastructure uses the "Diameter is
RADIUS based.

The Diameter Credit Control" (DCC) protocol, Control Application [RFC4006] describes how to
implement a prepaid accounting system using a Diameter based
infrastructure.

The translation agent that enables the interoperation of both systems, functionality between a Diameter Credit Control and a
RADIUS prepaid protocol interaction is desirable. This also applies vice versa, i.e. described in scenarios where
the AAA infrastructure uses RADIUS and the service metering device
uses Diameter. Appendix B.

6. Security Considerations

The idea extended RADIUS protocol described in this document is subject to
a number of such potential attacks, in a translation agent would be manner similar to convert incoming RPP
(resp. DCC) messages into outgoing DCC (resp. RPP) messages. It
would be, in principle, desirable for the translation agent to RADIUS
protocol without these extensions. It is recommended that IPsec be
stateless. That is,
employed to protect against certain of the agent attacks.

[Editor's Note: This section is freaking short. We should not add
something here.]

7. Table of Attributes

The following table provides a guide which attributes may be required to internally
maintain information about each ongoing found in
which RADIUS or Diameter session.
However, under the current specification of RPP messages, and DCC, this appears
to be impossible due to in what quantity.

Request Accept Reject Challenge Accounting # Attribute
Request
0-1 0 0 0 0 TBD PPAC
0+ 0+ 0 0 0+ TBD PPAQ
0+ 0+ 0 0 0+ TBD PTS

8. IANA Considerations

This document contains a number of reasons. These include the
following.

1. The transport mechanism for DCC is TCP, which requires per-
session state instructions to be maintained at both endpoints IANA.

8.1. New RADIUS Attributes

This document requires the assignment of new RADIUS attributes type
numbers for the
communication. Note, however, that, in principle, each DCC
message could be sent over a dedicated TCP connection which is
torn down as soon as following attributes:

Attribute Name | Attribute Type Value
--------------------------------------+-----------------------------
Prepaid-Accounting-Capability (PPAC) | TBD
Prepaid-Accounting-Operation (PPAQ) | TBD
Prepaid Tariff Switching (PTS) | TBD

8.2. New Registry: Prepaid SubTypes

Section 4 defines the message is sent. This, however, SubTypes used within newly defined attributes.
IANA is
likely asked to be unacceptable in terms create a registry for these SubTypes. Each registry
entry consists of efficiency.

2. While RPP messages encode the cumulative amount a 8 bit number together with a description of consumed/
requested resources, DCC messages carry the difference from the
previous message.
SubType. This means that the translation agent has to
maintain document creates the current amount following SubTypes for this
registry:

The semantic of consumed/requested resources the above-listed SubTypes is described in
order to be able to calculate Section 4.

Following the correct amount to be put into
an outgoing message.

The translator maps each incoming RPP (resp. DCC) message into an
outgoing DCC (resp. RPP) message, policies outline in [RFC3575] the available SubTypes
(i.e., value 0 and possibly establishes or updates
local state that is associated values 26-255) with the session. The translated
(i.e. outgoing) message is a function description of their
semantic will be assigned after Expert Review initiated by the incoming message as well
as existing state that is associated O&M
Area Directors in consultation with the current session.

Translation occurs on an attribute-by-attribute basis. Certain
attributes are translated without consideration RADEXT working group chairs
or the working group chairs of local per-session
state. Other attributes, namely those that are bound to a particular
session, require such consideration. The translation agent has to
identify the session (and possibly subsession) an incoming message
belongs to in order to consult the appropriate local per-session
state.

Note that certain DCC attributes cannot designated successor working group.
Updates can be translated due to their
semantics not being present in RPP, and vice versa. This results in provided based on expert approval only. A designated
expert will be appointed by the messages, in which these attributes occur, not being delivered O&M Area Directors. No mechanism to
their intended destination. In such cases it is desirable
mark entries as "deprecated", or to inform
the originator about delete entries from the failure and terminate registry
is envisioned.

Each registration must include a number for the session.

In each scenario (i.e. RPP client / DCC AAA infrastructure SubType and DCC
client / RPP AAA infrastructure), the translator operates in two
directions, namely RPP to DCC and vice versa. In
semantic of the following
sections, SubType.

8.3. New Registry: Update-Reason

Section 4.2.10 defines the notation c->s means that Update-Reason SubType. IANA is asked to
create a registry for the attribute values contained in question may
occur only the Update-Reason
SubType, as shown in Figure 11. Each registry entry consists of a 8
bit number together with a description of the direction from update reason.

Following the client to policies outline in [RFC3575] the server. The
notation s->c denotes available values
together with a description of their semantic will be assigned after
Expert Review initiated by the converse and O&M Area Directors in consultation
with the notation c<->s denotes
that RADEXT working group chairs or the attribute may occur in messages that are directed in either
direction.

5.1. Session Identification

The translation agent has to keep per-session state in order to
perform its task. A session may working group chairs of a
designated successor working group. Updates can be identified provided based on
expert approval only. A designated expert will be appointed by the RPP
identifier
O&M Area Directors. No mechanism to mark entries as "deprecated", or
to delete entries from the DCC session identifier. That is, registry is envisioned.

8.4. New Registry: Termination-Action

Section 4.2.14 defines the translation
agent should always maintain Termination-Action SubType. IANA is asked
to create a pair of (RPP, DCC) session identifiers
and maintain registry for the per-session state values contained in association with that pair.
This per-session state must be addressable by either of these two
identifiers. Moreover, an RPP session identifier must uniquely
correspond to a DCC identifier. (If this holds, the converse also
holds.) Termination-
Action SubType, as shown in Figure 12. Each subsession identifier within an RPP session must also
uniquely correspond to registry entry consists
of a subsession identifier within its
corresponding DCC session. (If this holds the converse also holds.)

5.2. Translation between RADIUS prepaid client and Diameter Credit
Control AAA infrastructure

This section describes 8 bit number together with a description of the translator in termination
action.

Following the "RPP client / DCC AAA
infrastructure" case. In other words, policies outline in this section it is assumed
that the client "talks" RPP and [RFC3575] the AAA inftrastructure "talks" DCC.
The translator is assumed to sit somewhere in available values
together with a description of their semantic will be assigned after
Expert Review initiated by the middle and to
mediate between client and server.

For each RPP AVP (i.e. AVP that is specified O&M Area Directors in consultation
with the present
document), RADEXT working group chairs or the transformation into working group chairs of a semantically equivalent DCC AVP
(if such an AVP exists), along with what per-session state
designated successor working group. Updates can be provided based on
expert approval only. A designated expert will be appointed by the
translator has
O&M Area Directors. No mechanism to create mark entries as "deprecated", or consult,
to delete entries from the registry is described. For clarity of
exposition, each RPP AVP envisioned.

8.5. New Registry: Requested-Action

Section 4.2.17 defines the Requested-Action SubType. IANA is addressed in asked
to create a separate subsection.
Since in this scenario, registry for the PPC is typically values contained in the initiator Requested-Action
SubType, as shown in Figure 13. Each registry entry consists of a session, 8
bit number together with a description of the focus is on requested reason.

Following the RPP AVPs.

5.2.1. PPAC (c<->s)

A DCC client is assumed to always support Volume metering, Duration
metering, Resource metering, Pools, Rating groups, and Tariff
Switching. Thus, if policies outline in [RFC3575] the available values
together with a PPAQ that indicates any description of their semantic will be assigned after
Expert Review initiated by the above is sent
client->server, the translator does O&M Area Directors in consultation
with the following: It lets message go
through but remembers what exactly RADEXT working group chairs or the client supports. If working group chairs of a
designated successor working group. Updates can be provided based on
expert approval only. A designated expert will be appointed by the
server later requests (servier -> client direction) an unsupported
metering
O&M Area Directors. No mechanism to be performed, send failure mark entries as "deprecated", or
to server and cause delete entries from the
session to be terminated at registry is envisioned.

8.6. New Registry: Check-Balance-Result

Section 4.2.18 defines the client.

If Check-Balance-Result SubType. IANA is
asked to create a PPAC indicates support registry for multiple services (0x00000020), the
translator maps this onto values contained in the Check-
Balance-Result SubType, as shown in Figure 14. Each registry entry
consists of a DCC Multiple-Services- Indicator AVP.

5.2.2. Service Termination Attribute (c->s)

The Diameter base protocol assumes that 8 bit number together with a description of the client always supports
dynamic session termination. If this AVP is present,
requested reason.

Following the translator
does not need to do anything, i.e. there exists no DCC AVP that this
AVP can policies outline in [RFC3575] the available values
together with a description of their semantic will be mapped to. If this AVP is absent, assigned after
Expert Review initiated by the message O&M Area Directors in which it
appears should either be discarded and originator should be informed
of a failure, consultation
with the RADEXT working group chairs or the message working group chairs of a
designated successor working group. Updates can be passed provided based on (without this AVP being
mapped onto a DCC AVP). However, in the latter case,
expert approval only. A designated expert will be appointed by the translator
has
O&M Area Directors. No mechanism to remember that the client does not support dynamic termination.
Thus, the translatior has mark entries as "deprecated", or
to initiate the normal session termination
procedure with the client when (if) dynamic termination is later
initiated by delete entries from the server.

5.2.3. Quota Identifier Attribute (c<->s)

When quota registry is allocated for the first time by envisioned.

8.7. New Registry: AvailableInClient-Extended

Section 4.2.18 defines the DCC server, PrePaid Accounting Capability (PPAC)
attribute with the
translator has AvailableInClient-Extended field. IANA is asked
to create a QID AVP, registry for the values contained in the
AvailableInClient-Extended field, as required by this
specification. The translator later uses shown in Section 4.1. Each
registry entry consists of a QID AVP 8 bit number together with a description
of the capability. Note that this is sent in a bitmask and only 8 values are
available for registration via IANA.

Following the client-to-server direction policies outline in order to identify [RFC3575] the corresponding
DCC session. The QID has to be saved in the translator's per session
state.

5.2.4. Volume Quota Attribute (c<->s)

If this AVP occurs in a message that is sent in the server-to-client
direction, it is translated into a Granted-Service-Unit AVP with an
embedded CC-Total-Octets AVP. [editor's note: this sentence belongs
to the other translation type, i.e. AAA = RPP and client = DCC.]

If this AVP occurs in a message that is sent in the client-to-server
direction, then it is translated into a Used-Service-Unit AVP with an
embedded CC-Total-Octets AVP. Note that only the difference between
current cumulative quota for the (sub)session and the quota in
incoming messages is indicated in the translated DCC message. Local
state is updated with cumulative consumed resources.

Conversely, if the server grants quota using the DCC Granted-Service-
Unit AVP with an embedded CC-Total-Octets AVP, then the translation
agent must translate this into a Volume Quota Attribute. Again,
local state must be consulted so that the cumulative amount of octets
is indicated in the Volume Quota attribute.

5.2.5. Duration Quota Attribute (c<->s)

If this AVP occurs in a message that is sent in the server-to-client
direction, it is translated into a Granted-Service-Unit AVP with an
embedded CC-Time AVP. [editor's note: this sentence belongs to the
other translation type, i.e. AAA = RPP and client = DCC.]

If this AVP occurs in a message that is sent in the client-to-server
direction, then it is translated into a Used-Service-Unit AVP with an
embedded CC-Time AVP. Note that only the difference between current
cumulative quota for the (sub)session and the quota in incoming
messages is indicated in the translated DCC message. Local state is
updated with cumulative consumed resources (i.e. time).

Conversely, if the server grants quota using the DCC Granted-Service-
Unit AVP with an embedded CC-Time AVP, then the translation agent
must translate this into a Duration Quota attribute. Again, local
state must be consulted so that the cumulative amount of seconds is
indicated in the Duaration Quota attribute.

5.2.6. Resource Quota Attribute (c<->s)

If this AVP occurs in a message that is sent in the server-to-client
direction, it is translated into a Granted-Service-Unit AVP with an
embedded CC-Service-Specific-Units AVP. [editor's note: this sentence
belongs to the other translation type, i.e. AAA = RPP and client =
DCC.]

If this AVP occurs in a message that is sent in the client-to-server
direction, then it is translated into a Used-Service-Unit AVP with an
embedded CC-Service-Specific-Units AVP. Note that only the
difference between current cumulative quota for the (sub)session and
the quota in incoming messages is indicated in the translated DCC
message. Local state is updated with cumulative consumed resources
(i.e. resources).

Conversely, if the server grants quota using the DCC Granted-Service-
Unit AVP with an embedded CC-Service-Specific-Units AVP, then the
translation agent must translate this into a Resource Quota
attribute. Again, local state must be consulted so that the
cumulative amount of resource units is indicated in the Resource
Quota attribute.

Note that the "resource" type is application dependent. This means
that a DCC application unit corresponds to n RPP application units,
where n may be any real number. If n is not 1, then the RPP/DCC
translator must be aware of that and translate resource units
accordingly.

5.2.7. Value Digits Attribute (c<->s)

The encoding of this AVP is similar in RPP and DCC, and the value it
holds may have to be evaluated in conjunction with an acommpanying
"Exponent" AVP. It should be kept in mind that, in RPP the
cumulative amount of granted/consumed quota is typically encoded into
an AVP of this type, while in DCC only the difference from a previous
message.

5.2.8. Exponent Attribute (c<->s)

The encoding of this AVP is similar in RPP and DCC, and the value it
holds may have to be evaluated in conjunction with an acommpanying
"Value Digits" AVP. It should be kept in mind that, in RPP the
cumulative amount of granted/consumed quota is typically encoded into
a related "Value Digits" and "Exponent" AVP pair, while in DCC only
the difference from a previous message is encoded into such a pair.

5.2.9. Volume/Duration/Resource Threshold Attributes (s->c)

In DCC the concept of "threshold" does not exist. Instead, the DCC
client is assumed to ask for the replenishment of quota in good time.
In RPP, on the other hand, the server may optionally include a
threshold AVP, as an indication to the PPC about when to ask for
quota replenishment.

Thus, in this scenario, there is no need for the translator to ever
include a threshold attribute into the messages that it sends to the
PPC. If, however, there is a need for a threshold attribute to be
present in order to avoid a possible service provision

5.2.10. Update Reason Attribute (c->s)

The DCC AVP that is semantically closer to the Update Reason AVP than
any other AVP is the CC-Request-Type AVP. This AVP indicates whether
the message is which it appears is intended to indicate an "initial",
an "intermediate" or a "final interrogation". Morever, in case of
the session being terminated at the client, it indicates the reason
for this termination.

The following list lists the possible available values of an "Update Reason"
attribute, along
together with corresponding values for the CC-Request-Type
AVP.

o Pre-initialization: No action/value defined.

o Initial Request: Typically an "intial interrogation" is triggered
as a result description of the reception of the message that contains this
Update Reason AVP. Hence, CC-Request-Type AVP indicates
"INITIAL_REQUEST".

o Threshold Reached: The reception of the message containing this
Update Reason AVP typically triggers an "intermediate
interrogation". Hence, CC-Request-Type AVP indicates
"UPDATE_REQUEST".

o Quota Reached: The reception of the message containing this Update
Reason AVP typically triggers an "intermediate interrogation".
Hence, CC-Request-Type AVP indicates "UPDATE_REQUEST".

o TITSU Approaching: The reception of the message containing this
Update Reason AVP typically triggers an "intermediate
interrogation". Hence, CC-Request-Type AVP indicates
"UPDATE_REQUEST".

o Remote Forced Disconnect: Reception of such an Update Reason
indicates that the client has terminated the session. The
corresponding value for the CC-Request-Type AVP is
"TERMINATION_REQUEST".

o Client Service Termination: Reception of such an Update Reason
indicates that the client has terminated the session. The
corresponding value for the CC-Request-Type AVP is
"TERMINATION_REQUEST".

o "Access Service" Terminated: Reception of such an Update Reason
indicates that the client has terminated the session. The
corresponding value for the CC-Request-Type AVP is
"TERMINATION_REQUEST".

o Service not established: Reception of such an Update Reason
indicates that the client has terminated the session. The
corresponding value for the CC-Request-Type AVP is
"TERMINATION_REQUEST".

o One-Time Charging: Such an Update Reason indicates that a one-time
charging event is their semantic will be assigned after
Expert Review initiated by the client. The corresponding
value for the CC-Request-Type AVP is "EVENT_REQUEST". Note that a
"Requested-Action: AVP MUST also be included O&M Area Directors in consultation
with the outgoing DCC
message. Typically, this would be of the type "DIRECT_DEBITING", RADEXT working group chairs or "REFUND_ACCOUNT", depending on other AVPs present in the
message.

5.2.11. PrepaidServer Attribute (s<->c)

The PPC typically never sets the value working group chairs of a PrepaidServer attribute.
Instead, it repeats those values that it receives from the AAA
infrastructure, in this scenario from the translator. This attribute
is therefore not used in a translation scenario. Nevertheless, the
translator must make sure that messages about the same RPP session
are forwarded to the same DCC server, throughout the whole session.
This may
designated successor working group. Updates can be easy to guarantee since the transport of Diameter is TCP.

5.2.12. Service-ID Attribute (s<->c)

The DCC equivalent of a RPP "Service-ID" AVP is the combination of
Service-Context-Id and Service-Identifier AVPs. The translator must
keep a static equivalence table of the RPP Service-ID and the
corresponding DCC combination in order to correctly translate an RPP
service identifier into DCC and back.

5.2.13. Rating-Group-ID Attribute (s<->c)

The DCC equivalent of a RPP "Rating-Group-ID" AVP is also called a
"Rating-Group-ID". Depending on the configuration, this AVP may
contain the same value provided based on both the RPP and the DCC side of the
communication. If, however, static rating groups are configured
between the RCC client and the translator, and different rating
groups between the DCC server and the translator, then the translator
has to maintain a static translation table for the rating group
identifier. In any case, the translation of a rating group AVP, is
not a function of the translator's local per-session state.

5.2.14. Termination-Action Attribute (s->c)

The DCC equivalent of the "Termination-Action" AVP is called the
"Final-Unit-Action" AVP. In this scenario (RPP client and DCC AAA
infrastructure), a DCC "Final-Unit-Action" AVP is translated into a
"Termination-Action" AVP. The following list contains the possible
"Final-Unit-Action" values along with their "Termination-Action"
equivalent.

o TERMINATE (DCC): This value has a direct equivalent in RPP, also
called "Terminate".

o REDIRECT (DCC): If this value appears in a "Final-Unit-Action"
AVP, then a "Redirect-Server-Address" AVP must also appear in the
same DCC message. The translator translates these two AVPs into a
"Termination-Action" with value "Redirect/Filter" and an
eqiovalent NAS-Filter-Rule attribute (specified in http://
www.ietf.org/internet-drafts/draft-ietf-radext-ieee802-00.txt).

o RESTRICT_ACCESS (DCC): If this value appears in a "Final-Unit-
Action" AVP, then a "Restriction-Filter-Rule" AVP must also appear
in the same DCC message. The translator translates these two AVPs
into a "Termination-Action" with value "Redirect/Filter" and an
eqiovalent Filter-ID attribute (specified in http://www.ietf.org/
internet-drafts/draft-ietf-radext-ieee802-00.txt).

o In the absence of a "Final-Unit-Action" AVP, the DCC server
assumes that the DCC client
expert approval only. A designated expert will ask for replenishment of quota at
some suitable time. In RPP, this is explicitly conveyed via a
"Termination-Action" AVP with the value "Request More Quota".
Thus, in the absence of a "Final-Unit-Action" AVP, the translator
in this scenario appends such an AVP into the outgoing RPP
message.

5.2.15. Pool-ID Attribute (s<->c)

The DCC equivalent of a RPP "Pool-ID" AVP is also called a "Pool-ID".
Typically, no translation needs to be done to the "Pool-ID"
attribute.

5.2.16. Multiplier Attribute (s<->c)

The multiplier attribute, which is a pair of "Value-Digits" and
"Exponent" AVPs, typically needs no translation, since the value it
carries (inside a "Value-Digits" and an "Exponent" AVP) represents
the rating of appointed by the service or rating group
O&M Area Directors. No mechanism to which it refers, with
respect mark entries as "deprecated", or
to abstract units. As such, the same multiplier value would
typically applyt be conveyed delete entries from a DCC server to an PPC, and vice
versa.

5.2.17. Requested-Action Attribute (c->s)

The "Requested Action" AVP can be directly translated into its DCC
equivalent, which carries the same name.

1. Balance Check (PCC): CHECK_BALANCE (DCC)

2. Price Enquiry (PCC): PRICE_ENQUIRY (DCC)

5.2.18. Check-Balance-Result Attribute (s->c)

This attribute carries only a binary value. Hence, its translation registry is straightforward.

5.2.19. Cost-Information Attribute (s->c)

This attribute consists of a Value-Digits AVP, an Exponent AVP, a
Currency Code AVP, and a Cost-Unit AVP. All these AVPs do likewise
exist in DCC, and carry identical semantics in the context of the
"Cost-Information" AVP. Thus, the translation of this attribute is
straightforward.

5.2.20. VolumeUsedAfterTariffSwitch attribute (c->s)

This attribute carries the amount of octets that were consumed after
a tariff change. It always appears in a message with an accompanying
PPAQ attribute in which the total amount of octets (i.e. those that
were consumed both before and after the tariff switch) is reported.
Thus, the translation agent can compute the amount of octets that
were consumed before the tariff change.

In DCC, the two amounts, i.e. the octets that were consumed before a
tariff change and those that were consumed afterwards, are reported
in separate Used-Service-Unit AVPs. The two Used-Service-Unit AVPs
have an embedded CC-Total-Octets AVP that indicates the appropriate
amount of octets. Furthermore, the Used-Service-Unit AVP that
carries the amount that was consumed before the tariff switch also
carries an embedded Tariff-Change-Usage AVP with the value
UNIT_BEFORE_TARIFF_CHANGE (0). Similarly, the Used-Service-Unit AVP
that carries the amount that was consumed after the tariff switch
also carries an embedded Tariff-Change-Usage AVP with the value
UNIT_AFTER_TARIFF_CHANGE (1).

6. Security Considerations

The extended RADIUS protocol described in this document is subject to
a number of potential attacks, in a manner similar to the RADIUS
protocol without these extensions. It is recommended that IPsec be
employed to protect against certain of the attacks.

7. IANA Considerations

This document requires the assignment of new Radius attributes type
numbers for the following attributes. Prepaid-Accounting-Capability
(PPAC), AvailableInClient, Prepaid-Accounting-Operation (PPAQ),
QuotaIdentifier, (QID), VolumeQuota (VQ), VolumeTreshold (VT),
DurationQuota (DQ), DurationTreshold (DT), UpdateReason (UR),
PrePaidServer (PPS), ServiceID (SID), Rating-Group-ID (RGID),
TerminationAction (TA), PoolID (PID), PoolMultiplier (PM), Cost-
Information (COST), Session-Termination-Capability (STC),
PrepaidTariffSwitch (PTS), TariffSwitchInterval (TSI) and others.

8. envisioned.

9. Acknowledgements

The authors would like to thank Christian Guenther for his valuable
insight Guenther, Bernard Aboba,
and John Loughney for their feedback and his active and ongoing contributions that he
provided throughout the development of
this document.

10. References

9.1.

10.1. Normative References

[1] Bradner, S., "RFC 2026: The Internet Standards Process --
Revision 3", October 1996.

[2]

[RFC2119] Bradner, S., "RFC 2119: Key words for use in RFCs to
Indicate Requirement Levels", March 1997.

[3]

[RFC2865] Rigney, C., Rubens, A., Simpson, W., and S. Willens, "RFC
2865: Remote Authentication Dial In User Server (RADIUS)",
June 2000.

[4]

10.2. Informative References

[I-D.ietf-radext-filter-rules]
Congdon, P., "RADIUS Attributes for Filtering and
Redirection", draft-ietf-radext-filter-rules-03 (work in
progress), July 2007.

[RFC2284] Blunk, L. and J. Vollbrecht, "PPP Extensible
Authentication Protocol (EAP)", RFC 2284, March 1998.

[RFC2866] Rigney, C., "RFC 2866: RADIUS Accounting", June 2000.

[5]

[RFC2869] Rigney, C., Willats, W., and P. Calhoun, "RFC 2869: RADIUS
Extensions", June 2000.

[6] Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege, M., and
I. Goyret, "RFC 2868: RADIUS Attributes

[RFC3575] Aboba, B., "IANA Considerations for Tunnel Protocol
Support", June 2000.

[7] RADIUS (Remote
Authentication Dial In User Service)", RFC 3575,
July 2003.

[RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Adoba, "RFC 3576: Dynamic Authorization Extensions to
Remote Authentication Dial-In User Service (RADIUS)",
February 2003.

[8]

[RFC3748] Adoba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "RFC 3748: Extensible Authentication Protocol",
June 2004.

9.2. Informative References

[9]

[RFC4006] Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J.
Loughney, "RFC 4006: Diameter Credit Control Application",
August 2005.

Appendix A. Example flows

This section presents certain example flows that involve the RADIUS
prepaid extensions. By no means is the intent of this section to
specify or recommend business logic, rating strategies, and
application-level behaviour. The intent of this section is purely to
illustrate some fictive scenarios and the RADIUS prepaid message
flows that could be associated with these scenarios. The contents of
this section should be regarded as a collection of informative
examples that aim to provide guidance to implementors.

A.1. A simple flow

End user PPC AAA Server PPS

user logs on
------(1)--------->
Access Request
{RADIUS BASE AVPS,
PPAC=00...00011}
-------(2)-------->

RADIUS authentication
<--------------(3)---------------------->

Access Request
{RADIUS BASE AVPS,
PPAC=00...00011}
------(4)--------->

[allocates
5MB quota]

Access Response Accept
{RADIUS BASE AVPS,
PPAQ={QID=5, VQ = 5MB,
VTH = 4.5 MB}}
<-------(5)--------
forwards message
<-----(6)-----------
<-------(3)--------

service provision/metering
-------(7)--------->
-------(4)--------->

4.5 MB consumed

Access Request
{RADIUS BASE AVPS,
PPAQ={QID=5, VQ=4.5MB,
REASON=THRESHOLD REACHED}}
-------(8)--------->

forwards message
-------(9)------->
-------(5)--------->

[allocates another 7MB
to the access service]

Access Response Accept
{RADIUS BASE AVPS,
PPAQ={QID=8, VQ=12MB,
VTH = 11.5 MB}}
<----------(10)--------------
forwards message
<------(11)--------
<----------(6)--------------
user logs off
------(12)-------
------(7)-------
Access Request
{RADIUS BASE AVPS,
PPAQ={QID=8, VQ=7 MB,
REASON=ACCESS SERV TERMINATED}}
-------(13)--------->

forwards message
-------(14)------->
-------(8)--------->

[reimburses
user account]

AA Response
{RADIUS BASE AVPS}
<------(15)--------
AA Response Accept
{RADIUS BASE AVPS}
<------(16)--------
<-------(9)--------

Figure 12: 19: A simple example message flow

The user logs on (1). The PPC sends a RADIUS Access Request message
to the home AAA server PPS (2), and includes the prepaid-specific PPAC AVP. This AVP
indicates that both duration-based and volume-based metering is
supported. However, it also indicated that multiple services, rating
groups and resource pools are not supported. Note that, since this
is not an "Authorize-Only" message, no PPAQ AVP attribute with Update
Reason="initial request" is included (see Section 3.7.1). The
home AAA server PPS
then authenticates the user and authorizes the access service, as is
usual in RADIUS (3). RADIUS. Note that the PPAC AVP is appended by the PPC in at
least the last message that is sent to the home AAA server during
this possibly multiple-round exchange.

If authentication and authorization is successful (in this example
this is assumed), then the home AAA server forwards the final Access
Request to the PPS (4). The PPS identifies the user's prepaid account
from the included base RADIUS AVPs, and determines the capabilities
of the PPC from the PPAC attribute. Assuming that sufficient funds
are available in the user's prepaid account, the PPS reserves some of
these and rates the service. In this example, the PPS reserves, say,
2 Euros and determines that the access service is rated at 0.4 Euro
per MB. This results in 5 MB of quota being granted. The PPS also
determines that the PPC should ask for this quota to be replenished
once 4.5 MB have been consumed. Thus, it creates an Access Accept
message with a Volume-Threshold indication of 4.5MB. It further
associates the QuotaIdentifier QID=5 to this
quota reservation. This identifier can be
used to later uniquely identify the prepaid session, user, account,
etc. The resulting Access Accept message is sent to the home AAA server (5) and
forwarded to the PPC (6). (3).

Upon reception of message (6), (4), the PPC provides the access service to
the user and meters it accordingly. At some point in time, the
threshold is reached, i.e. i.e., 4.5MB of "access service" have been
consumed by the user. At that point, the PPC generates an Authorize-Only Authorize-
Only Access Request that contains the usual RADIUS attributes and a
PPAQ AVPs attributes that reports the amount of consumed quota, and the
request for replenishment, i.e. i.e., the Update-
Reason= Update-Reason= THRESHOLD REACHED (8).
(5). Note that the QID in this message is the same as the one
previously received from the user's home AAA
server. This message is forwarded to the PPS (9). PPS.

Upon reception of message (9), (5), the PPS identifies the user and his
account from the QID. In also determines that a prepaid session is
ongoing, and that enough credit remains in the prepaid account in
order for the access service to continue being provided. Since 4.5
MB have been consumed, the PPS subtracts 1.8 Euros from the user's
prepaid account. The PPS decides to reserve another 2.8 euros from
the user's account. (This results in 3 euros being reserved in total
at this point in time.) As the access service is rated at 0.4 euros
per MB, the PPS determines that another 7 MB of quota should be
granted. This results in a total cumulative quota allocation of 12
MB for the access service. The PPS further calculates the new
threshold value of 11.5 MB. Since this is a new quota reservation,
the PPS also allocates a new QuotaIdentifier QID to it, in this example QID=8. The
resulting RADIUS message is sent to the home AAA server
(10) and forwarded to the PPC (11). (6).

Upon reception of message (11), (6), the PPC updates its records and
continues provisioning access to the user. At some point the user
logs off (12). (7). The PPC must then report how many resources were
consumed, so that the PPC can subtract the appropriate monetary
amount from the user's prepaid account. To this end the PPC
constructs an Authorize-Only Access Request message with a PPAQ AVPs
attributes for the access service. In this example, 7 MB were
consumed by the access service in total. The PPC reports 7 MB its
final message
(13). This is forwarded to the (8). The PPS (14) which correlates the report, using the QID, to
the previous session state. It determines, from the previous
records, that the access service had consumed another 4.5 MB before
(as indicated in message (9)). (6)). This means that, of the 7 MB, only
3.5 MB have not yet been subtracted from the user's account. Thus,
the PPS subtracts another 1.4 euros from the user's account and,
since the session is to be terminated (REASON=ACCESS SERVICE
TERMINATED), releases any reserved monetary amount.

The PPS responds with an Access Response as required by the RADIUS
base specification (15). So does the home AAA server (16). (9).

A.2. A flow with prepaid tariff switching

End user PPC AAA Server PPS
user logs on
------(1)--------->
Access Request
{RADIUS BASE AVPS,
PPAC=00...00111}
-------(2)-------->

RADIUS authentication
<--------------(3)---------------------->

Access Request
{RADIUS BASE AVPS,
PPAC=00...00011}
------(4)--------->

[allocates
20MB quota]

Access Response Accept
{RADIUS BASE AVPS,
PPAQ={QID=5, VQ = 20MB,
VTH = 18 MB}, PTS={
QID=5, PTS{TSI=300sec,
TITSU=6000sec}}
<-------(5)--------
forwards message
<-----(6)-----------
<-------(3)-------

service provision/metering
-------(7)--------->
-------(4)--------->

5900 seconds have
passed
Access Request
{RADIUS BASE AVPS,
PPAQ={QID=5, VQ=14MB,
REASON=TITSU APPROACH.},
TSI={QID=5, VUATS=11MB}}
-------(8)--------->

forwards message
-------(9)------->
-------(5)--------->

[allocates another 10MB
to the access service]

Access Response Accept
{RADIUS BASE AVPS,
PPAQ={QID=8, VQ=30MB,
VTH = 28 MB},PTS={
QUD=8, PTS=95 sec}}
<----------(10)--------------
forwards message
<------(11)--------
<----------(6)--------------

user logs off
------(12)-------
------(7)-------

Access Request
{RADIUS BASE AVPS,
PPAQ={QID=8, VQ=17 MB,
REASON=ACCESS SERV TERMINATED},
PTS={QID=8, VUATS=2.5 MB}
-------(13)--------->

forwards message
-------(14)------->
-------(8)--------->

[reimburses
user account]

AA Response
{RADIUS BASE AVPS}
<------(15)--------
AA Response Accept
{RADIUS BASE AVPS}
<------(16)--------
<-------(9)--------

Figure 13: 20: Example message flow with Tariff Switch

The user logs on (1). The PPC sends a RADIUS Access Request message
to the home AAA server (2), and includes the prepaid-specific PPAC
AVP. This AVP indicates that both duration-based and volume-based
metering is supported, as well as tariff switching. The home AAA
server then authenticates may authenticate and user and authorizes authorize the access
service, as is usual in RADIUS (3). RADIUS. Note that the PPAC AVP is appended
by the PPC in at least the last message that is sent to the home AAA server PPS
during this possibly multiple-round exchange.

If authentication and authorization is successful (in this example
this is assumed), the home AAA server forwards the final Access
Request to the PPS (4). The PPS identifies the user's prepaid account from
the included base RADIUS AVPs, and determines the capabilities of the
PPC from the PPAC attribute. In this example, it is assumed that a
tariff switch is about to occur in 300 seconds from the current time.
Suppose that the access service is currently rated at 0.5 euros per
MB and in the next tariff period it is rated at 0.6 euros per MB.
Suppose further that a third tariff period is about to start in 6000
seconds from current time and that that access service is rated at
0.8 euros per MB in that period. The PPS then decides to reserve 12
euros from the user's account. Since it is conceivable that the user
may consume all allocated quota in the (more expensive) "0.6-euro"
period, the PPS reserves 20 MB of quota, and determines a threshold
value of 18 MB. It constructs a Radius Access Accept message with a
PPAQ attribute that reflects these choices, and carries a QuotaIdentifier Quota
Identifier QID=5. It further adds a PTS AVP in the message which is
linked to the PPAQ via the common QID value. The PTS AVP contains a
TSI attribute indicating that a tariff switch will occur in 300
seconds. It also includes a TITSU attribute with the value of 6000
seconds. This is included in order to make sure that the PPC will
report the consumed quota before the "2-euro" tariff period will
start. The message is sent to the AAA server (5) and
forwarded to the PPC (6). (3).

Upon reception of message (6), (3), the PPC provides the access service to
the user and meters it accordingly (7). (4). It also keeps track of time.

That is, it remembers how many octets are consumed before and how
many after the tariff switch that will take place in 300 seconds.

In this example it is assumed that the user consumes the allocated
quota rather slowly. In particular, nearly 6000 seconds (the value
indicated by TITSU) TITSU SubType) pass without the threshold of 18 MB being
reached. The PPC notices this and must therefore report usage and
request the quota to be replenished despite the fact that the
threshold has not been reached. In this example, it decides to do so
100 seconds before the 6000 seconds are reached. To this end, it
constructs an Authorization Access Request message including a PPAQ
that indicates that 14 MB have been consumed up to now. It also
includes a PTS AVP attribute in order to indicate, using the VUATS AVP,
SubType, that 11 MB of these were consumed after the tariff switch.
The message is sent to the AAA server (8) and forwarded to the PPS (9). (5).

The PPS can link the message to previous session state via the QID.
It now rates the consumed volume as follows. The 11 MB that were
consumed after the tariff switch correspond to 11 * 0.6 = 6.6 euros
and the remaining 14-11=3 MB to 3 * 0.5 = 1.5 euros. Thus, the PPS
subtracts the amount of 6.6+1.5=8.1 euros from the user's account,
which leads to a remainder of 12 - 8.1 = 3.9 euros being reserved.

The PPS now determines that message (9) (5) was sent in order to
replenish the quota for this prepaid session. This can be deduced
from the UPDATE REASON field, which indicates that the PPC sent this
message because the time indicated by the TITSU AVP SubType is
approacing. The PPS now determines that enough credit remains in the
user's prepaid account in order for the access service to continue
being provided and decides to reserve another 8.9 euros from the
user's account. Since it is conceivable that the user will consume
the 6 unused MB of quota from the previous allocation, as well as the
entire quota that is to be allocated now, entirely in the "0.8-euro"
period, the quota that should now be granted in addition to the
previous 20 MB should be 10 MB. This is because 0.9 of the 8.9 euros
are being reserved in order to "cover the worst case scenario". The
fact that 0.9 euros are reserved for this purpose is due to the fact
that the unused 6 MB from the previous allocation correspond to 4.8
euros (with 0.8 euros per MB). This is 4.8 - 3.9 = 0.9 euros more
than the amount of funds that are still "reserved" from the previous
allocation. (After this reservation, the total amount of reserved
money is 8.9 + 3.9 = 12.8 euros, which corresponds to 16 (10+6) MB
being consumed in the "0.8-euro" period.)

Since quotas are encoded in a cumulative way in RADIUS, the PPS
includes a VolumeQuota of 30 MB into the Access Accept message (10). (6).
The PPS further calculates the new threshold value of 28 MB. Since
this is a new quota reservation, the PPS also allocates a new
QuotaIdentifier QID to
it, in this example QID=8. The resulting RADIUS message is sent to
the home AAA server (10) and forwarded to the PPC
(11). (6).

Upon reception of message (11), (6), the PPC updates its records and
continues providing access to the user. At some point the user logs
off (12). (7). The PPC must then report how many resources were consumed,
so that the PPC can subtract the appropriate monetary amount from the
user's prepaid account. To this end the PPC constructs an Authorize-
Only Access Request message with a PPAQ AVPs attributes for the access
service. In this example, 17 MB were consumed by the access service
in total. The PPC reports 17 MB its final message (13). This is forwarded to
the (8). The PPS (14) which
correlates the report, using the QID, to the previous session state.
It determines, from the previous records, that the access service had
consumed 14 MB before (as indicated in message (9)). (5)). This means
that, of the 17 MB, only the monetary equivalent for 3 MB have not
yet been subtracted from the user's account. The PPS calculates how
much should be deducted from the user's account as follows. Since
the VUATS AVP SubType indicates that 2.5MB were consumed after the tariff
switch, only 0.5 MB were consumed before that. Thus, the monetary
equivalent is 0.5 * 0.6 + 2.5 * 0.8 = 3.6 euros. That is, the PPS
subtracts 3.6 euros from the user's prepaid account. Since the
session has by now be terminated by the PPC (REASON=ACCESS SERVICE
TERMINATED), the PPS now releases any reserved monetary amount, in
this example 12.8 - 3.6 = 9.2 euros.

The PPS responds with an Access Response as required by the RADIUS
base specification (15). So does the home AAA server (16). (9).

Remark: In this example, two tariff switches take place. In other
scenarios, of course, only one tariff switch may occur. In such
scenarios the TITSU AVP SubType is not used.

A.3. Resource pools and Rating Groups

End user PPC AAA Server PPS

user logs on
------(1)--------->

Access Request
{RADIUS BASE AVPS,
PPAC=00...00101111}
-------(2)-------->

RADIUS authentication
<--------------(3)---------------------->

Access Request
{RADIUS BASE AVPS,
PPAC=00...00101111}
------(4)--------->

[allocates
5MB quota]

Access Response Accept
{RADIUS BASE AVPS,
PPAQ={QID=5, VQ = 5MB,
poolID=1,mult=1}}
<-------(5)--------
forwards message
<-----(6)-----------
<-------(3)--------

service provision/metering
-------(7)--------->
-------(4)--------->

user requests service A
-------(8)--------->
-------(5)--------->

Access Request
{RADIUS BASE AVPS,PPAQ={
SID="A", RGROUP=1}}
-------(9)-------->
forwards message
-----(10)--------->
-------(6)-------->

[allocates 50 min
quota]

Access Response Accept
{RADIUS BASE AVPS,
PPAQ={QID=7, DQ=3000sec
poolID=1,RGROUP=1, SID="A"
mult=1747.63}}

<---------(11)---------------
forwards message
<----(12)--------
<---------(7)---------------

user requests service B
-------(13)-------->
-------(8)-------->

Pool 1 close to exhaustion

Access Request
{RADIUS BASE AVPS,
PPAQ={QID=5, VQ=4MB,
REASON=QUOTA REACHED,
PoolID=1, mult=1}
PPAQ={QID=7, DQ=3300sec
REASON=QUOTA REACHED,
PoolID=1, mult=1747.63,
SID="A",RGROUP=1}}
-------(14)--------->

forwards message
-------(15)------->
-------(9)--------->

[allocates another
3 MB to access service
and 30 minutes to
service "A"]

Access Response Accept
{RADIUS BASE AVPS,
PPAQ={QID=8, VQ=8MB,
PoolID=1, mult=1, RGROUP=1},
PPAQ={QID=9, DQ=4800sec
PoolID=1, mult=1747.63,
SID="A"}}
<----------(16)--------------
forwards message
<------(17)--------
\ <----------(10)--------------

user logs off
------(18)-------
------(11)-------
Access Request
{RADIUS BASE AVPS,
PPAQ={QID=8, VQ=6.5MB,
REASON=ACCESS SERV TERMINATED,
PoolID=1, mult=1}
PPAQ={QID=9, DQ=5400sec
REASON=ACCESS SERV TERMINATED,
PoolID=1, mult=1747.63,
SID="A",RGROUP=1}}
-------(19)--------->

forwards message
-------(20)------->
-------(12)--------->

[reimburses
user account]

AA Response
{RADIUS BASE AVPS
<------(21)--------
AA Response Accept
{RADIUS BASE AVPS
<------(22)--------
<------(13)--------

Figure 14: 21: Example message flow with resource pools and rating groups

The user logs on (1). The PPC sends a RADIUS Access Request message
to the home AAA server PPS (2), and includes the prepaid-specific PPAC AVP,
indicating that multiple services, rating groups and resource pools
are supported. Note that, since this is not an "Authorize- Only"
message, no PPAQ AVP attribute with Update Reason="initial request" is
included (see Section 3.7.1). The home AAA server PPS then authenticates may authenticate the user
and authorizes authorize the access service, as is usual in RADIUS
(3). RADIUS. Note that
the PPAC AVP is appended by the PPC in at least the last message that
is sent to the home AAA server PPS during this possibly multiple-round exchange.

If authentication and authorization is successful (in this example
this is assumed), the home AAA server forwards the final Access
Request to the PPS (4). The PPS identifies the user's prepaid account from
the included base RADIUS AVPs, and determines the capabilities of the
PPC from the PPAC attribute. Assuming that sufficient funds are
available in the user's prepaid account, the PPS reserves some of
these and rates the service. In this example, the PPS reserves 5
Euros and determines that the access service is rated at 1 Euro per
MB. In anticipation that the user requests more chargeable services
throughout this prepaid session, and since this is supported by the
PPC, the PPS further associates a resource pool with this
reservation, in this example PoolID=1. The PPC also specifies the
multiplier = 1 for the access service. Note that, since 5MB =
5242880 octets, 1 unit in the resource pool corresponds to 5 /
5242880 euros, which is about 0.000095367431640625 Eurocents.
(However, the PPC does not need to know that.) Moreover, the PPS
associates the QuotaIdentifier QID=5 to this quota reservation. This identifier can be
used to later uniquely identify the prepaid session, user, account,
etc. The resulting Access Accept message is sent to the home AAA server (5) and forwarded to the PPC (6). (3).

Upon reception of message (6), (3), the PPC provides the access service to
the user and meters it accordingly. accordingly (4). That is, for every octet
consumed, the PPC subtracts 1 unit (since the multiplier is 1) from
the resouce pool with PoolID=1.

At some point in time, the user requests another chargeable service,
namely service A (8). (5). The PPC generates an Authorize-Only Access
Request that contains the usual RADIUS attributes and the Service-ID
identifying service A (9). (6). The PPC has determined that service A is
rated in an identical way as at least one more service. Thus,
service A has been configured to belong to a rating group, in this
example the group with Rating-Group-ID=1. This identifier is
included is message (9), which is then forwarded to the PPS (10). (6).

Upon reception of message (10), (6), the PPS identifies the user and his
account from the base RADIUS attributes, the fact that a prepaid
session is ongoing, and determines that enough credit remains in the
prepaid account in order for service A to be provided. The PPS also
determines that service A is rated at 0.10 euros per minute. The PPS
decides to reserve another 5 euros from the users account; this
corresponds to 50 minutes or, as encoded in the DurationQuota AVP,
SubType, 3000 seconds. As service A draws from the same prepaid
account as the access service, the PPS associates this reservation
with the same resource pool as the previous reservation (QID=5),
namely the pool with PoolID=1. Note that, in order for the abstract
units in the pool to be consistent, the multiplier has to be 1747.63.
This is because each second corresponds to about 0.10 / 60 = 0.00167
euros, which is about 1747.63 times the value of an abstract resource
pool unit, as this was determined by the first allocation of quota to
the pool (i.e. (i.e., 0.000095367431640625 Eurocents). Since this is a new
quota reservation, the PPS also allocates a new QuotaIdentifier QID to it, in this
example QID=7. The resulting RADIUS message is sent to the home AAA server (11) and forwarded to the PPC (12). (7).

Upon reception of message (12), (7), the PPC adjusts the units in resource
pool 1. That is, it first determines how much quota had been
allocated to service A in the past, and subtracts this from the quota
reservation found in the message. Since this is the first quota
reservation for service A, there is nothing to subtract. Thus, it
adds 3000 * 1747.63 = 5242890 units to the pool and remembers that
3000 seconds have been allocated to service A during this prepaid
session. The PPC then provides service A to the user, and meters it
against resource pool 1. That is, for every second it subtracts
1747.63 units from the pool.

At some point in time, the user requests service B (13). (8). The PPC
determines that service B is rated exactly in the same way as service
A, i.e. i.e., that they belong to the same rating group, namely the one
with Rating-Group-ID=1. Since this rating group has been effectively
authorised by the allocation of quota with QID=7, the PPC provides
service B to the user immediately. It is rated in the same way as
service A, i.e. i.e., for every second provided, 1747.63 units are
subtracted from credit pool 1.

At some point in time, resource pool 1 is close to exhaustion. (For
example, the PPC may determine that the pool is "close to exhaustion"
when has less than 10% its initial amount of units.) At that point,
the PPC needs to ask for replenishment for the pool. Suppose that,
at that point in time, 4MB of "access service", 45 minutes of
"service A", and 10 minutes of "service B" were provided to the user.
Note that this corresponds to (4*1048576) + (55*60*1747.63) = 4194304
+ 5767179 = 9961483 abstract service units from the pool. The PPC
constructs an Authorize-Only Access Request message that reports the
usage for the "access service" and "service A". This message
contains two PPAQ AVPS, attributeS, is sent to the home AAA server (14) and
forwarded to the PPS (15). (9). Note that is
the message it appears that "service A" has consumed more than it was
allocated (i.e. (i.e., 55 minutes although only 50 minutes were initially
allocated to it). This is not a a problem since the PPS knows that
"service A" was drawing from the same pool as the "access service"
and that the "access service" did only consume 4 out of the 5 MB it
was allocated.

Upon reception of message (15), (9), the PPS subtracts 4 euros from the
user's account for the "access service" and another 5.5 euros for
"service A". (This includes the charge incurred by "service B" up to
that point in time, although the PPS is not aware of "service B"
being provisioned to the user.) The PPS then determines that
sufficient funds remain in the prepaid account in order for both
services to be continued. The PPS decides to reserve another 3MB for
the access service and 30 minutes for "service A". This corresponds
to 3+3=6 euros. Since in RADIUS prepaid the quotas are encoded in a
cumulative manner, the PPAQ attribute that grants the quota for the
"access service" contains a Volume-Quota AVP SubType of 8MB (8388608
octets), which is the 5MB that were initially allocated, plus the 3MB
allocated now. The resource pool identifier is, as previously,
PoolID=1 and the multiplier is 1. Similarly, the PPAQ that grants
quota for "service A" contains 4800 seconds (the initial 3000 plus
1800 that correspond to the 30 additional minutes). Again, the
PoolID=1 and multiplier=1747.63. The resulting Access Response
message is sent to the home AAA server (16) and forwarded to the PPC
(17). (10).

When the PPC received message (17) (10) it checks how much quota has been
allocated previously to the "access service". It finds that the
answer is 5MB (5242880 octets); thus, out of the 8MB (8388608 octets)
that are indicated by the PPAQ with QID=8, only 3MB (3145728 octets)
have not yet been added to resource pool 1. The PPC thus adds
3145728 abstract units to resource pool 1 (since the multiplier is
1). The PPC then acts similarly on the other PPAQ attribute that
exists in message (17). (11). That is, the PPC determines that 3000
seconds of quota for "service A" had already been added to the pool.
Thus only 1800 out of the 4800 should be additionally added to the
pool. Since the applicable multiplier here is 1747.63, the PPC adds
further 3145734 abstract units to the pool 1.

The PPC then continues to provide the access service, "service A" and
"service B" to the user, and meters them against the pool, as
previously.

At some point the user logs off (18). (11). The PPC must then report how
many resources were consumed, so that the PPC can subtract the
appropriate monetary amount from the user's prepaid account. To this
end the PPC constructs an Authorize-Only Access Request message with
two PPAQ AVPs; attributes; one for the access service and one for "service
A". Suppose that, in total, 6.5MB were consumed by the access
service, 70 minutes were consumed by "service A" and 20 minutes by
"service B". The PPC reports 6.5MB (6815744 octets) and 90 minutes
(5400 seconds) in its final message (19). This is forwarded to the (12). The PPS which determines, from
the previous records, that the access service consumed another 2.5MB
(since 4MB out of the 6.5MB were already reported in message (15), (9), and
that "service A" consumed further 600 seconds. This corresponds to
2.5 + (600/60)*0.1 = 2.5+1=3.5 2.5+ 1=3.5 euros. Thus, the PPS only subtracts
2.5 out of the 6 previously reserved euros from the user's prepaid
account and responds with an Access Response as required by the
RADIUS base specification. specification (13).

A.4. One-time charging
End user PPC PPS

user requests ring tone
------(1)--------->

Access Request
{RADIUS BASE AVPS,
PPAQ={QID=321, SID=X, RQ=650,
REASON=10 (ONE-TIME CHARGING}}
-------(2)--------->

[rates 650 abstract units
deducts from user's account]

Access Accept
{RADIUS BASE AVPS}
<----------(3)--------------

ring tone is delivered
<------(4)-------

Figure 22: Example message flow with one-time charging

The user requests a chargeable ring tone (1). The PPC sends a RADIUS
Access Request message to the PPS (2), and includes a PPAQ attribute
with Update Reason="one-time charging" is included (see
Section 3.7.6). The Service ID indicates to the PPS that the
charging event is connected to a ring tone, so that the PPS can rate
the event accordingly. The PPAQ also contains a unique Quota
Identifier.

The PPS then may authenticate the user as is usual in RADIUS. If
authentication is successful (in this example this is assumed), the
home AAA server likewise forwards the PPC converts the 650 reported abstract
units into monetary value, according to the service type, and debit
the user's account accordingly. This happens, of course, only if
sufficient funds are available in the user's prepaid account. The
PPC then responds with an an Access Response. Accept message (3). The PPS adds
a "session timeout = 0 AVP" (see Section 3.7.6).

A.5. Price enquiry
End user PPC PPS

user requests AoC
------(1)--------->

Access Request
{RADIUS BASE AVPS,
PPAQ={SID=X, VQ=10MB,
REQ_ACT=2(PRICE ENQUIRY}}
-------(2)--------->

[rates 10MB for requested
service]

Access Accept
{RADIUS BASE AVPS,
PPAQ={SID=X, VQ=10MB,
COST INFORMATION= 0.6 euros
per MB}}
<----------(3)--------------

AoC is delivered
<------(4)-------

Figure 23: Example message flow with price enquiry (advice of charge)

Please refer to Section 2.7.2 for an explanation of this message
flow.

A.6. Balance check
End User PPC PPS

Access Request
{RADIUS BASE AVPS,
PPAQ={SID=X, VQ=10MB,
REQ_ACT=BALANCE CHECK}}
-------(2)--------->

[rates requested
Service and checks
remaining funds]

Access Accept
{RADIUS BASE AVPS,
PPAQ={SID=X, VQ=10MB,
BALANCE_CHECK_RESULT}}
<----------(3)--------------

Figure 24: Example message flow with balance check

Please refer to Section 2.7.3 for an explanation of this message
flow.

Appendix B. Translation between RADIUS Prepaid and Diameter Credit
Control

In scenarios where the service metering device uses the "RADIUS
prepaid" (RPP) protocol for accounting and prepaid charging while the
AAA infrastructure uses the "Diameter Credit Control" (DCC) protocol,
a translation agent that enables the interoperation of both systems,
is desirable. This also applies vice versa, i.e., in scenarios where
the AAA infrastructure uses RADIUS and the service metering device
uses Diameter.

The idea of such a translation agent would be to convert incoming RPP
(resp. DCC) messages into outgoing DCC (resp. RPP) messages. It
would be, in principle, desirable for the translation agent to be
stateless. That is, the agent should not be required to internally
maintain information about each ongoing RADIUS or Diameter session.
However, under the current specification of RPP and DCC, this appears
to be impossible due to a number of reasons. These include the
following.

1. The transport mechanism for DCC is TCP, which requires per-
session state to be maintained at both endpoints of the
communication. Note, however, that, in principle, each DCC
message could be sent over a dedicated TCP connection which is
torn down as soon as the message is sent. This, however, is
likely to be unacceptable in terms of efficiency.

2. While RPP messages encode the cumulative amount of consumed/
requested resources, DCC messages carry the difference from the
previous message. This means that the translation agent has to
maintain the current amount of consumed/requested resources in
order to be able to calculate the correct amount to be put into
an outgoing message.

The translator maps each incoming RPP (resp. DCC) message into an
outgoing DCC (resp. RPP) message, and possibly establishes or updates
local state that is associated with the session. The translated
(i.e., outgoing) message is a function of the incoming message as
well as existing state that is associated with the current session.

Translation occurs on an attribute-by-attribute basis. Certain
attributes are translated without consideration of local per-session
state. Other attributes, namely those that are bound to a particular
session, require such consideration. The translation agent has to
identify the session (and possibly subsession) an incoming message
belongs to in order to consult the appropriate local per-session
state.

Note that certain DCC attributes cannot be translated due to their
semantics not being present in RPP, and vice versa. This results in
the messages, in which these attributes occur, not being delivered to
their intended destination. In such cases it is desirable to inform
the originator about the failure and terminate the session.

In each scenario (i.e., RPP client / DCC AAA infrastructure and DCC
client / RPP AAA infrastructure), the translator operates in two
directions, namely RPP to DCC and vice versa. In the following
sections, the notation c->s means that the attribute in question may
occur only in the direction from the client to the server. The
notation s->c denotes the converse and the notation c<->s denotes
that the attribute may occur in messages that are directed in either
direction.

B.1. Session Identification

The translation agent has to keep per-session state in order to
perform its task. A session may be identified based on the RPP
identifier or the DCC session identifier. That is, the translation
agent should always maintain a pair of (RPP, DCC) session identifiers
and maintain the per-session state in association with that pair.
This per-session state must be addressable by either of these two
identifiers. Moreover, an RPP session identifier must uniquely
correspond to a DCC identifier. (If this holds, the converse also
holds.) Each subsession identifier within an RPP session must also
uniquely correspond to a subsession identifier within its
corresponding DCC session. (If this holds the converse also holds.)

B.2. Translation between RADIUS Prepaid and Diameter Credit Control

This section describes the translator in the "RPP client / DCC AAA
infrastructure" case. In other words, in this section it is assumed
that the client "talks" RPP and the AAA inftrastructure "talks" DCC.
The translator is assumed to sit somewhere in the middle and to
mediate between client and server.

For each RPP AVP (i.e., AVPs that are specified in the present
document), the transformation into a semantically equivalent DCC AVP
(if such an AVP exists), along with what per-session state the
translator has to create or consult, is described. For clarity of
exposition, each RPP AVP is addressed in a separate subsection.
Since in this scenario, the PPC is typically the initiator a session,
the focus is on the RPP AVPs.

B.2.1. PPAC (c<->s)

A DCC client is assumed to always support Volume metering, Duration
metering, Resource metering, Pools, Rating groups, and Tariff
Switching. Thus, if a PPAQ that indicates any of the above is sent
client->server, the translator does the following: It lets message go
through but remembers what exactly the client supports. If the
server later requests (servier -> client direction) an unsupported
metering to be performed, send failure to server and cause the
session to be terminated at the client.

If a PPAC indicates support for multiple services (0x00000020), the
translator maps this onto a DCC Multiple-Services- Indicator AVP.

B.2.2. Service Termination Attribute (c->s)

The Diameter base protocol assumes that the client always supports
dynamic session termination. If this AVP is present, the translator
does not need to do anything, i.e., there exists no DCC AVP that this
AVP can be mapped to. If this AVP is absent, the message in which it
appears should either be discarded and originator should be informed
of a failure, or the message can be passed on (without this AVP being
mapped onto a DCC AVP). However, in the latter case, the translator
has to remember that the client does not support dynamic termination.
Thus, the translatior has to initiate the normal session termination
procedure with the client when (if) dynamic termination is later
initiated by the server.

B.2.3. Quota Identifier Attribute (c<->s)

When quota is allocated for the first time by the DCC server, the
translator has to create a QID AVP, as required by this
specification. The translator later uses a QID AVP that is sent in
the client-to-server direction in order to identify the corresponding
DCC session. The QID has to be saved in the translator's per session
state.

B.2.4. Volume Quota Attribute (c<->s)

If this AVP occurs in a message that is sent in the server-to-client
direction, it is translated into a Granted-Service-Unit AVP with an
embedded CC-Total-Octets AVP.

B.2.5. Duration Quota Attribute (c<->s)

If this AVP occurs in a message that is sent in the server-to-client
direction, it is translated into a Granted-Service-Unit AVP with an
embedded CC-Time AVP.

B.2.6. Resource Quota Attribute (c<->s)

If this AVP occurs in a message that is sent in the server-to-client
direction, it is translated into a Granted-Service-Unit AVP with an
embedded CC-Service-Specific-Units AVP.

B.2.7. Value Digits Attribute (c<->s)

B.2.8. Exponent Attribute (c<->s)

B.2.9. Volume/Duration/Resource Threshold Attributes (s->c)

B.2.10. Update Reason Attribute (c->s)

The following list lists the possible values of an "Update Reason"
attribute, along with corresponding values for the CC-Request-Type
AVP.

o Pre-initialization: No action/value defined.

o Initial Request: Typically an "intial interrogation" is triggered
as a result of the reception of the message that contains this
Update Reason AVP. Hence, CC-Request-Type AVP indicates
"INITIAL_REQUEST".

o Threshold Reached: The reception of the message containing this
Update Reason AVP typically triggers an "intermediate
interrogation". Hence, CC-Request-Type AVP indicates
"UPDATE_REQUEST".

o Quota Reached: The reception of the message containing this Update
Reason AVP typically triggers an "intermediate interrogation".
Hence, CC-Request-Type AVP indicates "UPDATE_REQUEST".

o TITSU Approaching: The reception of the message containing this
Update Reason AVP typically triggers an "intermediate
interrogation". Hence, CC-Request-Type AVP indicates
"UPDATE_REQUEST".

o Remote Forced Disconnect: Reception of such an Update Reason
indicates that the client has terminated the session. The
corresponding value for the CC-Request-Type AVP is
"TERMINATION_REQUEST".

o Client Service Termination: Reception of such an Update Reason
indicates that the client has terminated the session. The
corresponding value for the CC-Request-Type AVP is
"TERMINATION_REQUEST".

o "Access Service" Terminated: Reception of such an Update Reason
indicates that the client has terminated the session. The
corresponding value for the CC-Request-Type AVP is
"TERMINATION_REQUEST".

o Service not established: Reception of such an Update Reason
indicates that the client has terminated the session. The
corresponding value for the CC-Request-Type AVP is
"TERMINATION_REQUEST".

o One-Time Charging: Such an Update Reason indicates that a one-time
charging event is initiated by the client. The corresponding
value for the CC-Request-Type AVP is "EVENT_REQUEST". Note that a
"Requested-Action: AVP MUST also be included in the outgoing DCC
message. Typically, this would be of the type "DIRECT_DEBITING",
or "REFUND_ACCOUNT", depending on other AVPs present in the
message.

B.2.11. PrepaidServer Attribute (s<->c)

The PPC typically never sets the value of a PrepaidServer attribute.
Instead, it repeats those values that it receives from the AAA
infrastructure, in this scenario from the translator. This attribute
is therefore not used in a translation scenario. Nevertheless, the
translator must make sure that messages about the same RPP session
are forwarded to the same DCC server, throughout the whole session.
This may be easy to guarantee since the transport of Diameter is TCP.

B.2.12. Service-ID Attribute (s<->c)

B.2.13. Rating-Group-ID Attribute (s<->c)

The DCC equivalent of a RPP "Rating-Group-ID" AVP is also called a
"Rating-Group-ID". Depending on the configuration, this AVP may
contain the same value on both the RPP and the DCC side of the
communication. If, however, static rating groups are configured
between the RCC client and the translator, and different rating
groups between the DCC server and the translator, then the translator
has to maintain a static translation table for the rating group
identifier. In any case, the translation of a rating group AVP, is
not a function of the translator's local per-session state.

B.2.14. Termination-Action Attribute (s->c)

o TERMINATE (DCC): This value has a direct equivalent in RPP, also
called "Terminate".

o In the absence of a "Final-Unit-Action" AVP, the DCC server
assumes that the DCC client will ask for replenishment of quota at
some suitable time. In RPP, this is explicitly conveyed via a
"Termination-Action" AVP with the value "Request More Quota".
Thus, in the absence of a "Final-Unit-Action" AVP, the translator
in this scenario appends such an AVP into the outgoing RPP
message.

B.2.15. Pool-ID Attribute (s<->c)

The DCC equivalent of a RPP "Pool-ID" AVP is also called a "Pool-ID".
Typically, no translation needs to be done to the "Pool-ID"
attribute.

B.2.16. Multiplier Attribute (s<->c)

The multiplier attribute, which is a pair of "Value-Digits" and
"Exponent" AVPs, typically needs no translation, since the value it
carries (inside a "Value-Digits" and an "Exponent" AVP) represents
the rating of the service or rating group to which it refers, with
respect to abstract units. As such, the same multiplier value would
typically applyt be conveyed from a DCC server to an PPC, and vice
versa.

B.2.17. Requested-Action Attribute (c->s)

The "Requested Action" AVP can be directly translated into its DCC
equivalent, which carries the same name.

1. Balance Check (PCC): CHECK_BALANCE (DCC)

2. Price Enquiry (PCC): PRICE_ENQUIRY (DCC)

B.2.18. Check-Balance-Result Attribute (s->c)

This attribute carries only a binary value. Hence, its translation
is straightforward.

B.2.19. Cost-Information Attribute (s->c)

B.2.20. VolumeUsedAfterTariffSwitch attribute (c->s)

This attribute carries the amount of octets that were consumed after
a tariff change. It always appears in a message with an accompanying
PPAQ attribute in which the total amount of octets (i.e., those that
were consumed both before and after the tariff switch) is reported.
Thus, the translation agent can compute the amount of octets that
were consumed before the tariff change.

In DCC, the two amounts, i.e., the octets that were consumed before a
tariff change and those that were consumed afterwards, are reported
in separate Used-Service-Unit AVPs. The two Used-Service-Unit AVPs
have an embedded CC-Total-Octets AVP that indicates the appropriate
amount of octets. Furthermore, the Used-Service-Unit AVP that
carries the amount that was consumed before the tariff switch also
carries an embedded Tariff-Change-Usage AVP with the value
UNIT_BEFORE_TARIFF_CHANGE (0). Similarly, the Used-Service-Unit AVP
that carries the amount that was consumed after the tariff switch
also carries an embedded Tariff-Change-Usage AVP with the value
UNIT_AFTER_TARIFF_CHANGE (1).

Authors' Addresses

Avi Lior
Bridgewater Systems
303 Terry Fox Drive
Ottawa, Ontario Suite 100
Canada

Email: avi@bridgewatersystems.com

Parviz Yegani
Cisco
Mobile Wireless Group, Cisco Systems
3625 Cisco Way, San Jose, California 95134
USA

Email: pyegani@cisco.com

Kuntal Chowdhury
Starent Networks
30 International Place, 3rd Floor
Tewksbury, MA 01876
USA

Email: kchowdhury@starentnetworks.com

Hannes Tschofenig
Nokia Siemens Networks
Otto-Hahn Ring 6
Munich, Bavaria 81739
Germany

Email: hannes.tschofenig@siemens.com hannes.tschofenig@nsn.com
URI: http://www.tschofenig.com

Andreas Pashalidis
Siemens
Otto-Hahn Ring 6
Munich, Bavaria 81739
NEC
Kurfuersten-Anlage 36
Heidelberg 69115
Germany

Email: andreas.pashalidis@siemens.com Andreas.Pashalidis@netlab.nec.de

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