On Demand Mobility ManagementActilityIstanbulTurkeyalper.yegin@actility.comIntel CorporationPetah TikvaIsraeldanny.moses@intel.comSungkyunkwan UniversitySuwonSouth Koreaseiljeon@skku.eduDMM Working GroupApplications differ with respect to whether they need session
continuity and/or IP address reachability. The network providing the
same type of service to any mobile host and any application running on
the host yields inefficiencies, as described in .
This document defines a new concep of enabling applications to influence the
network's mobility services (session continuity and/or IP address reachability)
on a per-Socket basis, and suggests extensions to the networking stack's API
to accomodate this concept.
In the context of Mobile IP ,
the following two attributes are defined for IP service provided to
mobile hosts:- Session ContinuityThe ability to maintain an ongoing transport interaction
by keeping the same local end-point IP address throughout the life-time of the IP
socket despite the mobile host changing its point of attachment within the IP
network topology. The IP address of the host may change after closing the IP socket
and before opening a new one, but that does not jeopardize the ability of applications
using these IP sockets to work flawlessly. Session continuity is essential for mobile
hosts to maintain ongoing flows without any interruption.- IP Address ReachabilityThe ability to maintain the same IP address
for an extended period of time. The IP address stays the same across
independent sessions, and even in the absence of any session. The
IP address may be published in a long-term registry (e.g., DNS), and
is made available for serving incoming (e.g., TCP) connections. IP
address reachability is essential for mobile hosts to use
specific/published IP addresses.Mobile IP is designed to provide both session continuity and IP
address reachability to mobile hosts. Architectures utilizing these
protocols (e.g., 3GPP, 3GPP2, WIMAX) ensure that any mobile host
attached to the compliant networks can enjoy these benefits. Any
application running on these mobile hosts is subjected to the same
treatment with respect to session continuity and IP address
reachability.Achieving session continuity and IP address reachability with
Mobile IP incurs some cost. Mobile IP protocol forces the mobile host's
IP traffic to traverse a centrally-located router (Home Agent, HA),
which incurs additional transmission latency and use of additional
network resources, adds to the network CAPEX and OPEX, and decreases the
reliability of the network due to the introduction of a single point of
failure . Therefore, session continuity
and IP address reachability SHOULD be provided only when necessary.In reality not every application may need
these benefits. IP address reachability is required for applications
running as servers (e.g., a web server running on the mobile host). But,
a typical client application (e.g., web browser) does not necessarily
require IP address reachability. Similarly, session continuity is not
required for all types of applications either. Applications performing
brief communication (e.g., text messaging) can survive without having session
continuity support.Furthermore, when an application needs session continuity, it may be
able to satisfy that need by using a solution above the IP layer, such
as MPTCP , SIP mobility , or an application-layer mobility solution. These
higher-layer solutions are not subject to the same issues that arise
with the use of Mobile IP since they can utilize the most direct data
path between the end-points. But, if Mobile IP is being applied to the
mobile host, the higher-layer protocols are rendered useless because
their operation is inhibited by Mobile IP. Since Mobile IP ensures
that the IP address of the mobile host remains fixed (despite the location
and movement of the mobile host), the higher-layer protocols never
detect the IP-layer change and never engage in mobility management.This document proposes a solution for applications running on
mobile hosts to indicate when establishing the network connection ('on
demand') whether they need session continuity or IP
address reachability. The network protocol stack on the mobile host, in
conjunction with the network infrastructure, provides the required
type of service. It is for the benefit of both the users and the
network operators not to engage an extra level of service unless it is
absolutely necessary. It is expected that applications and networks
compliant with this specification will utilize this solution to use
network resources more efficiently.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14 , when, they appear in all capitals,
as shown here. Enabling applications to indicate their mobility service requirements
e.g. session continuity and/or IP address reachability, comprises the
following steps:- The application indicates to the network stack (local to the
mobile host) the desired mobility service.- The network stack assigns a source IP address based on an IP prefix
with the desired services that was previously provided by the network.
If such an IP prefix is not available, the network stack performs the
additional steps below.- The network stack sends a request to the network for a new source
IP prefix that is associated with the desired mobility service.- The network responds with the suitable allocated source IP prefix
(or responds with a failure indication).- If the suitable source IP prefix was allocates, the network stack
constructs a source IP address and provides it to the application. This document specifies the new address types associated with
mobility services and details the interaction between the applications
and the network stack steps. It uses the Socket interface as an example
for an API between applications and the network stack. Other steps are
outside the scope of this document. Four types of IP addresses are defined with respect to mobility
management.- Fixed IP Address A Fixed IP address is an address with a guarantee to be valid for a
very long time, regardless of whether it is being used in any packet
to/from the mobile host, or whether or not the mobile host is
connected to the network, or whether it moves from one
point-of-attachment to another (with a different IP prefix) while it is
connected.Fixed IP addresses are required by applications that need both session
continuity and IP address reachability.- Session-lasting IP AddressA session-lasting IP address is an address with a guarantee to be
valid throughout the life-time of the socket(s) for which it was requested.
It is guaranteed to be valid even after the mobile host had moved from one
point-of-attachment to another (with a different IP prefix).Session-lasting IP addresses are required by applications that need
session continuity but do not need IP address reachability.- Non-persistent IP AddressThis type of IP address has no guarantee to exist after a mobile host
moves from one point-of-attachment to another, and therefore, no session
continuity nor IP address reachability are provided. The IP address is created
from an IP prefix that is obtained from the serving IP gateway and is not
maintained across gateway changes. In other words, the IP prefix may be released
and replaced by a new one when the IP gateway changes due to the movement of the
mobile host forcing the creation of a new source IP address with the updated
allocated IP prefix.- Graceful Replacement IP AddressIn some cases, the network cannot guarantee the validity of the provided
IP prefix throughout the duration of the opened socket, but can provide a limited
graceful period of time in which both the original IP prefix and a new one are
valid. This enables the application some flexibility in the transition from the
existing source IP address to the new one.This gracefulness is still better than the non-persistence type of address
for applications that can handle a change in their source IP address but require
that extra flexibility.Applications running as servers at a published IP address require a
Fixed IP Address. Long-standing applications (e.g., an SSH session)
may also require this type of address. Enterprise applications that
connect to an enterprise network via virtual LAN require a Fixed IP
Address.Applications with short-lived transient sessions can use
Session-lasting IP Addresses. For example: Web browsers.Applications with very short sessions, such as DNS clients and
instant messengers, can utilize Non-persistent IP Addresses. Even
though they could very well use Fixed or Session-lasting IP
Addresses, the transmission latency would be minimized when a
Non-persistent IP Addresses are used.Applications that can tolerate a short interruption in connectivity
can use the Graceful-replacement IP addresses. For example, a streaming
client that has buffering capabilities.IP address type selection is made on a per-socket granularity.
Different parts of the same application may have different needs. For
example, the control-plane of an application may require a Fixed IP
Address in order to stay reachable, whereas the data-plane of the same
application may be satisfied with a Session-lasting IP Address.At any point in time, a mobile host may have a combination of IP
addresses configured. Zero or more Fixed, zero or more Session-lasting,
zero or more Non-persistent and zero or more Graceful-Replacement
IP addresses may be configured by the IP stack of the host. The
combination may be as a result of the host policy, application demand,
or a mix of the two.When an application requires a specific type of IP address and such
an address is not already configured on the host, the IP stack SHALL
attempt to configure one. For example, a host may not always have a
Session-lasting IP address available. When an application requests
one, the IP stack SHALL make an attempt to configure one by issuing a
request to the network. If the operation fails, the IP stack SHALL
fail the associated socket request and return an error. If successful,
a Session-lasting IP Address gets configured on the mobile host. If
another socket requests a Session-lasting IP address at a later time,
the same IP address may be served to that socket as well. When the last
socket using the same configured IP address is closed, the IP address
may be released or kept for future applications that may be launched
and require a Session-lasting IP address.In some cases it might be preferable for the mobile host to request
a new Session-lasting IP address for a new opening of an IP socket
(even though one was already assigned to the mobile host by the
network and might be in use in a different, already active IP
sockets). It is outside the scope of this specification to define
criteria for choosing to use available addresses or choosing to request
new ones. It supports both alternatives (and any combination).It is outside the scope of this specification to define how the
host requests a specific type of prefix and how the network indicates
the type of prefix in its advertisement or in its reply to a request.The following are matters of policy, which may be dictated by the
host itself, the network operator, or the system architecture
standard: - The initial set of IP addresses configured on the host at boot
time.- Permission to grant various types of IP addresses to a requesting
application.- Determination of a default address type when an application does
not make any explicit indication, whether it already supports the
required API or it is just a legacy application. Backwards compatibility support is REQUIRED by the following 3 types
of entities: - The Applications on the mobile host- The IP stack in the mobile host- The network infrastructure Legacy applications that do not support the On-Demand functionality will use
the legacy API and will not be able to take advantage of the On-Demand
Mobility feature. Applications using the new On-Demand functionality should be aware that
they may be executed in legacy environments that do not support it. Such
environments may include a legacy IP stack on the mobile host, legacy network
infrastructure, or both. In either case, the API will return an error code and
the invoking applications may just give up and use legacy calls. New IP stacks (that implement On Demand functionality) MUST continue to support
all legacy operations. If an application does not use On-Demand functionality, the
IP stack MUST respond in a legacy manner. If the network infrastructure supports On-Demand functionality,
the IP stack SHOULD follow the application request: If the application
requests a specific address type, the stack SHOULD forward this
request to the network. If the application does not request an address
type, the IP stack MUST NOT request an address type and leave it to
the network's default behavior to choose the type of the allocated IP
prefix. If an IP prefix was already allocated to the host, the IP
stack uses it and may not request a new one from the network. The network infrastructure may or may not support the On-Demand
functionality. How the IP stack on the host and the network
infrastructure behave in case of a compatibility issue is outside the
scope of this API specification. defines new flags that may be used with
setsockopt() to influence source IP address selection for a socket. The list of
flags include: source home address, care-of address, temporary address, public
address CGA (Cryptographically Created Address) and non-CGA. When applications
require session continuity service, they SHOULD NOT set the flags specified
in .However, if an application erroneously performs a combination of (1) Use
setsockopt() to set a specific option (using one of the flags specified in
) and (2) Selects a source IP address type, the
IP stack will fulfill the request specified by (2) and ignore the flags set
by (1). The different service types (session continuity types and address reachability) associated
with the allocated IP address types, may be associated with different costs. The cost
to the operator for enabling a type of service, and the cost to applications using a
selected service. A malicious application may use these to generate extra billing of a
mobile subscriber, and/or impose costly services on the mobile operator. When costly
services are limited, malicious applications may exhaust them, preventing other
applications on the same mobile host from being able to use them. Mobile hosts that enables such service options, should provide capabilities for
ensuring that only authorized applications can use the costly (or limited) service
types. The ability to select service types requires the exchange of the association of
source IP prefixes and their corresponding service types, between the mobile host and
mobile network. Exposing these associations may provide information to passive
attackers even if the traffic that is used with these addressed is encrypted. To avoid profiling an application according to the type of IP addresses,
it is expected that prefixes provided by the mobile operator are associated to
various type of addresses over time. As a result, the type of address
could not be associated to the prefix, making application profiling based on the
type of address harder. The application or the OS should ensure that IP addresses regularly change
to limit IP tracking by a passive observer. The application should regularly
set the On Demand flag. The application should be able to ensure that session
lasting IP addresses are regularly changed by setting a lifetime for example
handled by the application. In addition, the application should consider the use
of graceful replacement IP addresses. Similarly, the OS may also associated IP addresses with a lifetime. Upon
receiving a request for a given type of IP address, after some time, the
OS should request a new address to the network even if it already has one IP
address available with the requested type. This includes any type of IP address.
IP addresses of type graceful replacement or non persistent should be
regularly renewed by the OS. The lifetime of an IP address may be expressed in number of seconds or
in number of bytes sent through this IP address. This document has no IANA considerations.This document was merged with .
We would like to acknowledge the contribution of the following people to that document as
well:We would like to thank Wu-chi Feng, Alexandru Petrescu, Jouni Korhonen,
Sri Gundavelli, Dave Dolson Lorenzo Colitti and Daniel Migault for their valuable
comments and suggestions on this work.Following are some suggestions of possible extensions to the Socket API
for enabling applications to convey their session continuity and address
reachability requirements. introduced the ability of applications
to influence the source address selection with the IPV6_ADDR_PREFERENCE
option at the IPPROTO_IPV6 level. This option is used with setsockopt()
and getsockopt() calls to set/get address selection preferences.One alternative is to extend the defintion of the IPV6_ADDR_REFERENCE
opion with flags that express the invoker's desire. An "OnDeman" field could
contains one of the values: FIXED_IP_ADDRESS, SESSION_LASTING_IP_ADDRESS,
NON_PERSISTENT_IP_ADDRESS or GRACEFUL_REPLACEMENT_IP_ADDRESS.Another alternative is to define a new Socket function used by the invoker
to convey its desire. This enables the implementation of two behaviors of
Socket functions: The existing "setsockotp()" is a function that returns after
executing, and the new "setsc()" (Set Service Contionuity) function that may
initaite a request for the desired service, and wait until the network responds
with the allocated resources, before returning to the invoker.After obtaining an IP address with the desired behavior the application can
call the bind() Socket function to associate that received IP address with the
socket.