wdiff draft-ietf-ecrit-requirements-10.txt draft-ietf-ecrit-requirements-11.txt

ECRIT H. Schulzrinne
Internet-Draft Columbia U.
Expires: December 11, 3, 2006 R. Marshall, Ed.
TCS
June 9, 2006

Requirements for Emergency Context Resolution with Internet
Technologies
draft-ietf-ecrit-requirements-10.txt
draft-ietf-ecrit-requirements-11

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Abstract

This document defines terminology and enumerates requirements for the
context resolution of emergency calls placed by the public using
voice-over-IP (VoIP) and general Internet multimedia systems, where
Internet protocols are used end-to-end.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Terminology . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . 5
3. Basic . . . . . . . . . . . . . . . . . 6
3.1 Emergency Services . . . . . . . . . . . . . . . . . . . . 6
3.2 Service Providers . . . . . . . . . . . . . . . . . . . . 6
3.3 Actors . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.4 Call Routing Entities . . . . . . . . . . . . . . . . . . 7
3.5 Location . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.6 Identifiers, Numbers and Dial Strings . . . . . . . . . . 8
3.7 Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. High-Level Requirements Basic Actors . . . . . . . . . . . . . . . . . . . . . . 12 . . 11
5. High-Level Requirements . . . . . . . . . . . . . . . . . . 14
6. Identifying the Caller's Location . . . . . . . . . . . . . . 15
6. 16
7. Emergency Service Identifier . . . . . . . . . . . . . . . . . 18
7. 19
8. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 21
8. 22
9. Security Considerations . . . . . . . . . . . . . . . . . . . 25
9. 27
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
10. 28
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 27
11. 29
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
12. 30
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
12.1. 31
13.1 Normative References . . . . . . . . . . . . . . . . . . 29
12.2. 31
13.2 Informative References . . . . . . . . . . . . . . . . . 29 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30 32
Intellectual Property and Copyright Statements . . . . . . . . . . 31 33

1. Introduction

Users of both voice-centric (telephone-like) and non voice type non-voice services (e.g.,
such as text communication for hearing disabled users (RFC 3351 [2]) have an expectation [3])
expect to be able to initiate a request for help in case of an
emergency.

Unfortunately, the existing mechanisms to support emergency calls
that have evolved within the public circuit-switched telephone
network (PSTN) are not appropriate to handle evolving IP-based voice,
text and real-time multimedia communications. This document outlines
the key requirements that IP-based end systems and network elements,
such as SIP Session Initiation Protocol (SIP) [2] proxies, need to
satisfy in order to provide emergency call services, which at a
minimum, offer the same functionality as existing PSTN services, with
the additional overall goal of making emergency calling more robust,
less costly to implement, and multimedia-capable.

This document only focuses on end-to-end IP-based calls, i.e., where
the emergency call originates from an IP end system and terminates
into in
an IP-capable PSAP, conveyed entirely over an IP network.

Outlined within this

We first define terminology in Section 3. The document are then outlines
various functional issues which relate to placing an IP-based
emergency call, including a description of baseline requirements
(Section 4), 5), identification of the emergency caller's location
(Section 5), 6), use of an a service identifier to declare a call to be an
emergency call (Section 6), 7), and finally, the mapping function
required to route the call to the appropriate PSAP (Section 7). 8).

The primary intent purpose of the mapping protocol is to produce a PSAP URI
(from
drawn from a preferred set of URI schemes such as SIP or SIPS URIs, e.g., SIP:URI, SIPS:URI)
based on both location information [6] [9] and a service identifier in
order to facilitate the IP end-to-end completion of an emergency
call.

Aside from obtaining a PSAP URI, the mapping protocol is useful for
obtaining other information as well. There may be a case, for
example, where an appropriate dial string emergency number is not known, only
location. The mapping protocol can then return a geographically
appropriate dial string emergency number based on the input.

Since some PSAPs may not immediately support IP, or because some end
devices (UAs) user
equipment (UE) may not initially support emergency service URNs,
identifiers, it may be necessary to also support emergency service
identifiers that utilize less preferred URI schemes, such as a tel
URI in order to complete an emergency call via the PSTN.

Identification of the caller, while not incompatible with the
requirements for messaging outlined within this document, is
considered to be outside the scope of this document.

Location is required for two separate purposes, first, to support the
routing of the emergency call to the appropriate PSAP and second, to
display the caller's location to the call taker for to help in
dispatching emergency assistance to the appropriate location.

2. Requirements Terminology

In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [1],
with the qualification that unless otherwise stated these words apply
to the design of the mapping protocol, not its implementation or
application.

3. Terminology

3.1 Emergency Services

Basic emergency service: Basic Emergency Service emergency service allows a user caller to
reach a PSAP serving its current location, but the PSAP may not be
able to determine the identity or geographic location of the
caller, except by having the call taker ask asking the caller.

Enhanced emergency service: Enhanced In enhanced emergency services add service, the
ability to identify PSAP
call taker can determine the caller's identity or location to basic
emergency services. (Sometimes, only the caller location may be
known, e.g., when a call is placed from a public access point that
is not owned by an individual.) current location.

3.2 Service Providers

Internet Attachment Provider (IAP): An organization that provides
physical and layer 2 data link (layer 2) network connectivity to its
customers or users, e.g., through digital subscriber lines, cable
TV plants, Ethernet, leased lines or radio frequencies. Examples
of such organizations include telecommunication carriers,
municipal utilities, larger enterprises with their own network
infrastructure, and government organizations such as the military.

Internet Service Provider (ISP): An organization that provides IP
network-layer services to its customers or users. This entity may
or may not provide the physical-layer and layer-2 data link (layer-2)
connectivity, such as fiber or Ethernet, i.e., it may or may not be
play the role of an IAP.

Application Service Provider (ASP): The organization or entity that
provides application-layer services, which may include voice (see
"Voice Service Provider"). This entity can be a private
individual, an enterprise, a government, or a service provider.
An ASP is more general than a Voice Service Provider, since
emergency calls may use other media beyond voice, including text
and video. For a particular user, the ASP may or may not be the
same organization as his IAP or ISP.

Voice Service Provider (VSP): A specific type of Application Service
Provider which provides voice related services based on IP, such
as call routing, a SIP URI, or PSTN termination. In this
document, unless noted otherwise, any reference to "Voice Service
Provider" or "VSP" may be used interchangeably with "Application/
Voice Service Provider" or "ASP/VSP".

3.3 Actors

(Emergency) caller: The term "caller" or "emergency caller" refer to
the person placing an emergency call or sending an emergency
instant message (IM).

User Equipment (UE): User equipment is the device or software
operated by the caller to place an emergency call. A SIP user
agent (UA) is an example of a UE.

Call taker: A call taker is an agent at the PSAP that accepts calls
and may dispatch emergency help. Sometimes the functions of call
taking and dispatching are handled by different groups of people,
but these divisions of labor are not generally visible to the
caller and thus do not concern us here.

3.4 Call Routing Entities

Emergency Service Routing Proxy (ESRP): An ESRP is an emergency call
routing support entity that invokes the location-to-PSAP URI
mapping, to return either the URI for the appropriate PSAP, or the
URI for another ESRP. (In a SIP system, the ESRP would typically
be a SIP proxy, but may also be a Back-to-back back-to-back user agent
(B2BUA)).

Emergency Call Routing Support (ECRS): An intermediary function which
assists in the routing of an emergency call via IP. An ESRP is an
example of an emergency call routing support entity.

Public Safety Answering Point (PSAP): Physical location where
emergency calls are received under the responsibility of a public
authority. (This terminology is used by both ETSI, in ETSI SR 002
180, and NENA.) In the United Kingdom, PSAPs are called Operator
Assistance Centres, in New Zealand, Communications Centres.
Within this document, it is assumed, unless stated otherwise, that
PSAP is that which supports
PSAPs support the receipt of emergency calls over
IP. It is also assumed that the PSAP is reachable by IP-based
protocols, IP, using
appropriate application layer protocols such as SIP for call
signaling and RTP for media.

3.5 Location

Location: A geographic identification assigned to a region or feature
based on a specific coordinate system, or by other precise
information such as a street number and name. It can be either a
civic or geographic location.

Civic location: A described location based on some defined grid, reference system,
such as a jurisdictional, postal, metropolitan, jurisdictional region or rural reference
system, (e.g., postal delivery grid. A street address).
address is a common example of a civic location.

Geographic location: A reference to a point which is able to be
located as described by a set of defined coordinates within a
geographic coordinate system, (e.g., lat/lon such as latitude and longitude
within the WGS-84
datum). datum. For example, (2-D) 2-D geographic location is
defined as an
x,y (x,y) coordinate value pair according to the
distance North north or South south of the equator and East east or West west of the
prime meridian.

Location validation: A caller location is considered valid if the
civic or geographic location is recognizable within an acceptable
location reference system (e.g., USPS, WGS-84, etc.), United States Postal Address or
the WGS-84 datum) and can be mapped to one or more PSAPs. While
it is desirable to determine that a location exists, validation
may not ensure that such a location exists, but rather may only
ensure that the location falls within some range of known values.
Location validation ensures that a location is able to be
referenced for mapping, but makes no assumption about the
association between the caller and the caller's location.

(Location-dependent) emergency dial string: A location-dependent
emergency dial

3.6 Identifiers, Numbers and Dial Strings

(Emergency) service number: The (emergency) service number is a
string should be thought of as digits used to reach the digit sequence
that (emergency) service. The
emergency service number is often just called the emergency
number. It is the number typically dialed in order on devices directly
connected to reach the PSTN and the number reserved for emergency services. There are
two calls
by national or regional numbering authorities. It only contains
the digits 0 through 9, # and *. The service number may depend on
the location of the caller. For example, the general emergency
service number in the United States is 911 and the poison control
service number is 18002221222. In most cases, the service number
and dial strings described within this document, namely string are the same; they may differ in some private
phone networks. A service number may be carried in tel URLs [7],
along with a "home context identifier. In the North American numbering
plan, some service numbers are also three-digit N11 or service
codes, but not all emergency numbers have three digits. A caller
may have to dial string", and a "visited emergency service dial string".

Home emergency string (below) that differs from
the service number when using a PBX.

(Emergency) service dial string: A home emergency The service dial string represents a
(e.g., dialed) sequence identifies
the string of digits, digits that is used to initiate an
emergency call within a geographically correct location of a caller if it is considered must dial to be reach a user's "home" location or
vicinity.

Visited emergency particular
(emergency) service. In devices directly connected to the PSTN,
the service dial string: A visited emergency string is the same as the service number and may
thus depend on the location of the caller. However, in private
phone networks, such as in PBXs, the service dial string
represents a sequence consists
of digits that is used a dialing prefix to initiate reach an outside line, followed by the
emergency call within number. For example, in a geographically correct location of hotel, the
caller if outside dial string for
emergency services in the caller's "home" location United States might be 9911. Dial
strings may contain indications of pauses or vicinity. wait-for-secondary-
dial-tone indications. Service dial strings are outside the scope
of this document.

(Emergency) service identifier: A general The (emergency) service identifier
describes the emergency service, independent of the user interface
mechanism, the signaling protocol that has applicability is used to
both emergency reach the
service, or the caller's geographic location. It is a protocol
constant and non-emergency contexts (specifically referred
to used within this document as "emergency the mapping and signaling protocols. An
example is the service identifier"). URN [12].

(Emergency) service URL: The service URL is a protocol-specific
(e.g., SIP) or protocol-agnostic (e.g., im: [6]) contains the
address of the PSAP or other emergency service. It depends on the
specific signaling or data transport protocol used to reach the
emergency service.

Service URN: An A service URN is an implementation of a service
identifier, which has
applicability can be applied to both emergency and non-emergency contexts (e.g.,
urn:service:sos, urn:service:info, etc.) non-
emergency contexts, e.g., urn:service:sos or
urn:service:counseling. Within this document, service URN is specifically URNs are
referred to as 'emergency service URN'
[8].

Emergency service identifier (ESI): URNs' [12].

Home emergency number: A specific service identifier
that home emergency number is used to request a PSAP URI in order to initiate an the emergency call, and
number valid at the caller's customary home location, e.g., his
permanent residence. The home location may be used to mark any call as an emergency
call. An ESI is a more general term than 'emergency service URN',
since it could also refer to an alternate identifier, such as a
tel URI (Section 6).

Emergency service URN: An emergency-context specific or may not coincide
with the service URN that
is an implementation area of an the caller's VSP.

Home emergency service identifier (e.g.,
urn:service:sos). Is often referred to as, and dial string: A home dial string is equivalent with
'sos service URN'.

PSAP URI: The URI (e.g., SIP:URI, SIPS:URI, XMPP:URI, etc.) the dial string
valid at which the PSAP may be contacted with an caller's customary home location, e.g., his permanent
residence.

Visited emergency call. This contact
could be done directly, or via an intermediary, (e.g., ESRP). number: A visited emergency number is the emergency
number valid at the caller's current physical location. We
distinguish the visited emergency number if the caller is
traveling outside his home region.

Visited emergency dial string: A visited emergency dial string is the
dial string number valid at the caller's current physical
location.

3.7 Mapping
Mapping: The Mapping is the process of resolving a location to one or
more PSAP URIs which directly identify a PSAP, or point to an
intermediary which knows about a PSAP and that is designated as
responsible to serve for serving that location.

Mapping client: A mapping client interacts with the mapping server to
learn one or more PSAP URIs for a given location.

Mapping protocol: A protocol used to convey the mapping request and
response.

Mapping server: The mapping server holds information about the
location-to-PSAP URI mapping.

Mapping service: A network service which uses a distributed mapping
protocol to perform a mapping between a location and a PSAP, or
intermediary which knows about the PSAP, and is used to assist in
routing an emergency call.

(Emergency) caller: The term "caller" or "emergency caller" refer to
the person placing an emergency call or sending an emergency
instant message (IM).

4. Basic Actors

In order to support emergency services covering a large physical
area, various infrastructure elements are necessary, including: including
Internet Attachment Providers (IAPs), Application/Voice Service
Providers (ASP/VSPs), Emergency Call Service Routing Support (ECRS) Proxy (ESRP)
providers, mapping service providers, and PSAPs.

This section outlines which entities will be considered in the
routing scenarios discussed.

Location
Information +-----------------+
|(1) |Internet | +-----------+
v |Attachment | | |
+-----------+ |Provider | | Mapping |
| | | (3) | | Service |
| Emergency |<---+-----------------+-->| |
| Caller | | (2) | +-----------+
| |<---+-------+ | ^
+-----------+ | +----|---------+------+ |
^ | | Location | | |
| | | Information<-+ | |
| +--+--------------+ |(5) | | (6)
| | | | |
| | +-----------v+ | |
| (4) | |Emergency | | |
+--------------+--->|Call Routing|<--+---+ |
+--------------+--->| ESRP |<--+---+
| | | |Support | |
| | +------------+ |
| | ^ |
| | (7) | | +----+--+
| (8) | +------------>| |
+--------------+----------------------->| PSAP |
| | | |
|Application/ | +----+--+
|Voice |
|Service |
|Provider |
+---------------------+

Figure 1: Framework for emergency call routing

Figure 1 shows the interaction between the entities involved in the
call. There are a number of different deployment choices, as can be
easily seen from the figure.

How is location information provided to the end host? It might
either be known to the end host itself via manual configuration,
provided via GPS, made available via DHCP (RFC 3825 [4]) ([5], [14]) or some other mechanisms.
mechanism. Alternatively, location information is used as
part of call routing and inserted by
intermediaries.

Is the Internet Attachment Provider also the Application/Voice
Service Provider? In the Internet today these roles are typically
provided by different entities. As a consequence, the Application/
Voice Service Provider is typically not able to learn directly determine
the physical location of the emergency caller.

The overlapping squares in the figure indicate that some functions
can be collapsed into a single entity. As an example, the
Application/Voice Service Provider might be the same entity as the
Internet Attachment Provider. There is, however, no requirement that
this must be the case. Additionally, we consider that end systems
might act as their own ASP/VSP, e.g., either for enterprises or for
residential users.

Various potential interactions between the entities depicted in
Figure 1, 1 are described in the following:

(1) below:

1. Location information might be available to the end host itself.

(2)

2. Location information might, however, also be obtained from the
Internet Attachment Provider (e.g., using DHCP or application
layer signaling protocols).

(3)

3. The emergency caller might need to consult a mapping service to
determine the PSAP (or other relevant information) that is
appropriate for the physical location of the emergency caller,
possibly considering other attributes such as appropriate
language support by the emergency call taker.

(4)

4. The emergency caller might get assistance for emergency call
routing by infrastructure elements that are emergency call
routing support entities, (e.g., such as an Emergency Service Routing
Proxy (ESRP), (ESRP) in SIP).

(5) SIP.

5. Location information is used by emergency call routing support
entities for subsequent mapping requests.

(6)

6. Emergency call routing support entities might need to consult a
mapping service to determine where to route the emergency call.

(7)

7. For infrastructure-based emergency call routing (in contrast to
UE-based emergency call routing), the emergency call routing
support entity needs to forward the call to the PSAP.

(8)

8. The emergency caller (UE) may interact directly with the PSAP
(e.g., PSAP, where
the UE invokes mapping, and initiates a connection), connection, without
relying on any intermediary emergency call routing support
entities.

5. High-Level Requirements

Below, we summarize high-level architectural requirements that guide
some of the component requirements detailed later in the document.

Re1. Application/Voice service provider existence: The initiation of
an IP-based emergency call SHOULD NOT assume the existence of an
Application/Voice Service Provider (ASP/VSP).

Motivation: The caller may not have an application/voice service
provider. For example, a residence may have its own DNS domain
and run its own SIP proxy server for that domain. On a larger
scale, a university might provide voice services to its students
and staff, but might not be a telecommunication provider.

Re2. International applicability: Regional, political and
organizational aspects MUST be considered during the design of
protocols and protocol extensions which support IP-based emergency
calls.

Motivation: It must be possible for a device or software developed
or purchased in one country to place emergency calls in another
country. System components should not be biased towards a
particular set of emergency numbers or languages. Also, different
countries have evolved different ways of organizing emergency
services, e.g., either centralizing them or having smaller
regional subdivisions such as United States counties or
municipalities which handle emergency calls. calls within their jurisdiction.

Re3. Distributed administration: Deployment of IP-based emergency
services MUST NOT depend on a sole single central administration administrative
authority.

Motivation: The design of the mapping protocol must make it
possible to deploy and administer emergency calling features on a
regional or national basis without requiring coordination with
other regions or nations. The system cannot assume, for example,
that there is a single global entity issuing certificates for
PSAPs, ASP/VSPs, IAPs or other participants.

Re4. Multi-mode communication: IP-based emergency calls MUST support
multiple communication modes, including, for example, audio, video
and text.

Motivation: Within the PSTN, voice and text telephony (often
called TTY or text-phone in North America) are the only commonly
supported media. Emergency calling must support a variety of
media. Such media should include voice, conversational text (RFC
4103 [5]), [8]), instant messaging and video.

Re5. Alternate mapping sources: The mapping protocol MUST implement
a mechanism that allows for the retrieval of mapping information
from different sources.

Motivation: This provides the possibility of having available
alternative sources of mapping information when the normal source
is unavailable or unreachable.

Re6. Currency indication: The mapping protocol SHOULD support an
indicator describing how current the information provided by the
mapping source is.

Motivation: This is especially useful when an alternate mapping is
requested, and alternative sources of mapping data may not have
been created or updated with the same set of information or within
the same timeframe. Differences in currency between mapping data
contained within mapping sources should be minimized.

Re7. Mapping result usability: The mapping protocol MUST return one
or more URIs that are usable within a standard signaling protocol
(i.e., without special emergency extensions).

Motivation: For example, a SIP specific URI which is returned by the
mapping protocol needs to be usable by any SIP capable phone
within a SIP initiated emergency call. This is in contrast to a
"special purpose" URI, which may not be recognizable by a legacy
SIP device.

Re8.

Re6. PSAP URI accessibility: The mapping protocol MUST support
interaction between the client and server where no enrollment to a
mapping service exists or is required.

Motivation: The mapping server may well be operated by a service
provider, but access to the server offering the mapping must not
require use of a specific ISP or ASP/VSP.

Re9.

Re7. Common data structures and formats: The mapping protocol SHOULD
support common data structures and formats from the mapping
server. for location data.

Motivation: Location databases should not need to be transformed
or modified in any unusual or unreasonable way in order for the
mapping protocol to use the data. For example, a database which
contains civic addresses used by location servers may be used for
multiple purposes and applications beyond emergency service
location-to-PSAP URI mapping.

Re10.

Re8. Anonymous mapping: The mapping protocol MUST NOT require the
true identity of the target for which the location information is
attributed.

Motivation: Ideally, no identity information is provided via the
mapping protocol. Where identity information is provided, it may
be in the form of an unlinked pseudonym (RFC 3693 [3]).

5. [4]).

6. Identifying the Caller's Location

Location can either be provided directly, directly (by value), or by reference, via a poiner
(by reference), and represents either a civic location, or a
geographic location. An important question is how and when to attach
location information to the VoIP emergency signaling. signaling messages. In
general, we can distinguish three modes of operation of how a
location is associated with an emergency call:

UA-inserted: The caller's user agent inserts the location information
into the call signaling message. The location information is
derived from sources such as GPS, DHCP (see [4] [5] for geographic
location information and [10]) [14] for civic location information information) or
utilizing the Link Layer Discovery Protocol (LLDP) [see
IEEE8021AB]. [16].

UA-referenced: The caller's user agent provides a pointer (i.e., a
location reference), via a permanent or temporary identifier, to
the location information, which is stored by a location server
somewhere else and then retrieved by the PSAP, ESRP, or other
authorized service entity.

Proxy-inserted: A proxy along the call path inserts the location or
location reference.

The following requirements apply:

Lo1. Reference datum: The mapping protocol MUST support the WGS-84
coordinate reference system and MAY support other coordinate
reference systems.

Motivation: Though many different datums exist around the world,
this document recommends the WGS-84 datum is recommended here since it is designed to
describe the whole earth, rather than a single continent, etc.

Lo2. Location object/info preservation: The mapping protocol MUST
retain any location information which is provided to it, even
after mapping is performed.

Motivation: The ESRP continent or other
region, and the PSAP use the same location
information object, but for a different purpose. Therefore, it is
imperative that the mapping protocol does not remove the location
information from the messaging, so that it can be provided commonly used to the
PSAP.

Lo3. represent Global Positioning
System coordinates.

Lo2. Location delivery by-value: The mapping protocol MUST support
the delivery of location information using a by-value method,
though it MAY also support de-referencing a URL that references a
location object.

Motivation: The mapping protocol is not required to support the
ability to de-reference specific location references.

Lo4.

Lo3. Alternate community names: The mapping protocol MUST support
both the jurisdictional community name and the postal community
name fields within the PIDF-LO [9] data.

Motivation: A The mapping query protocol must be accepted accept queries with either
a postal or both jurisdictional community name fields, field, or both, and
provide appropriate responses. If a mapping query is made with contains only
one field present, community name and if the database contains both jurisdictional
and postal, postal community names, the mapping protocol response should SHOULD
return both.

Lo5. both community names.

Lo4. Validation of civic location: The mapping protocol MUST support
location validation for civic location locations (street addresses).

Motivation: Location validation provides an opportunity to help
assure
ascertain ahead of time, time whether or not a successful mapping to the
appropriate PSAP will likely occur when it is required.
Validation may also help to avoid delays during emergency call
setup due to invalid locations.

Lo6. location data.

Lo5. Validation resolution: The mapping protocol MUST support the
ability to provide ancillary information about the resolution of
location data used to retrieve a PSAP URI.

Motivation: The mapping server may not use all the data elements
in the provided location information to determine a match, or may
be able to find a match based on all of the information except for
some specific data elements. The uniqueness of this information
set may be used to differentiate among emergency jurisdictions.
Precision or resolution in the context of this requirement might
mean, for example, explicit identification of the data elements
that were used successfully in the mapping.

Lo7. Indication of non-existent location:

Lo6. Contact for location problems: The mapping protocol MUST
support a mechanism to indicate and contact an appropriate authority to resolve any associated
mapping-related issues
attributed for the queried location. For example, the
querier may want to a location report problems with the response values or a part of a location
indicate that is known to
not exist, despite the receipt of a successful mapping response.

Motivation: The emergency authority for database is mistaken on declaring a given jurisdiction
civic location as non-existent.

Motivation: Initially, authorities may provide URLs where a means to resolve addressing problems, e.g., a URI for a
web service that human
user can be used to report problems with an address.

Lo8. address or location. In
addition, web services may be defined to automate such reporting.
For example, the querier may wish to report that the mapping
database may be missing a newly-built or renamed street or house
number.

Lo7. Limits to validation: Successful validation of a civic location
MUST NOT be required to place an emergency call.

Motivation: In some cases, a civic location may not be considered
valid. This fact should not result in the call being dropped or
rejected by any entity along the call setup signaling path to the
PSAP.

Lo9.

Lo8. 3D sensitive mapping: The mapping protocol MUST implement
support for both 2D and 3D location information, and may accept
either a 2D or 3D mapping request as input.

Motivation: It is expected that end devices or location servers
will queriers may provide either 2D or
3D data. When a 3D request is presented within an area only
defined by 2D data within the mapping server, the mapping result
would be the same as if the height/altitude
dimension was height or altitude coordinate had been
omitted in from the mapping request.

Lo10.

Lo9. Database type indicator: The mapping protocol MAY support a
mechanism which provides an indication describing a specific
"type" type
of location database used.

Motivation: It is useful to know the source of the data stored in
the database used for location validation. This is applicable for validation, either for civic or
geographic location matching (e.g., USPS, MSAG,
GDT, etc.).

6. matching. In the United States, sources of
data could include the United States Postal Service, the Master
Street Address Guide (MSAG) or commercial map data providers.

7. Emergency Service Identifier

The term, service identifier, is a general term that incorporates all

Emergency service URNs [8], but which may also refer to other identifiers which are not service URNs, for example, a tel URI. In protocol exchanges,
any request constants that allow
protocol entities such as SIP proxy servers to invoke an distinguish emergency service along with
calls from non-emergency calls and to identify the specific
type of emergency
service desired, such as fire department or police,
is indicated by the desired. Emergency service URN.

Since this document addresses only emergency identifiers are a subclass of
service context specific
requirements for mapping, the terms identifiers that more generally identify services reachable
by callers. An example of a service identifier and is the service
URN, which have URN
[12], but other identifiers, such as tel URIs [7], may also serve
this role during a more general applicability than that of transition period.

Since this document only addresses emergency services, are replaced by we use the
terms "emergency service identifier" (ESI) and "emergency service URN", respectively,
throughout this document. The term "sos service URN" is used
interchangeably with "emergency service URN".

Id1. Emergency service identifier support: The mapping protocol MUST
be able to return one or multiple emergency service identifiers in
response to a query.

Motivation: Since there is a need for any device or network
element to recognize an emergency call throughout the call setup,
there is also a need to have the mapping protocol provide support "service identifier"
interchangeably. Requirements for such an identifier. This is regardless of the device location
or the ASP/VSP used. An example of this kind of identifier might
be the emergency service URN, 'urn:service:sos'.

Id2. Emergency service identifier resolution: Where multiple
emergency service these identifiers exist, the include:

Id1. Multiple emergency services: The mapping protocol MUST be able
to differentiate distinguish between ESIs based on the specific type of different emergency help requested. services,
differentiated by different service identifiers.

Motivation: Some jurisdictions may have offer multiple types of
emergency services available, (e.g., fire, police, ambulance), in
which case, it is important that any one could operate independently and can be selected
directly.

Id3. contacted
directly, for example, fire, police and ambulance services.

Id2. Extensible emergency service identifiers: The mapping protocol
MUST support an extensible list of emergency identifiers, though
it is not required to provide mapping mappings for every possible service.

Motivation: Extensibility is required since new emergency
services may be introduced over time, either globally or in some
jurisdictions. The use availability of an emergency service identifier is locally
determined.

Id4. services depends on
the locations. For example, the Netherlands are unlikely to offer
a mountain rescue service.

Id3. Discovery of emergency dial string: There number: The mapping protocol MUST be support for a
mechanism
able to discover an existing return the location-dependent emergency
dial string, (e.g., "9-1-1", "1-1-2"), contextually appropriate number for the
location of indicated in the caller. query.

Motivation: Users are trained to dial the appropriate emergency
dial string
number to reach emergency services. There needs to be a way to
figure out what the dial string is within emergency number at the local environment current location of the
caller.

Id5.

Id4. Home emergency dial string translation: There number recognition: User equipment MUST be support
for end device translation (e.g., SIP UA) of able
to translate a home emergency dial
string number into an emergency service
identifier.

Motivation: The UA would most likely UE could be pre-provisioned with the appropriate
information in order to make perform such a translation. The translation or could
discover the emergency number by querying the mapping protocol would be able to support either type for those
clients which may not support dial string translation.

Id6.
with its home location.

Id5. Emergency dial string number replacement: There SHOULD be support for
replacement of the original dial string emergency number with a reserved the appropriate emergency
service identifier for each signaling protocol used for an
emergency call. This replacement of the original dial string
should be call, based on local conventions, regulations, or
preference (e.g., as in the case of an enterprise).

Motivation: Any signaling protocol requires the use of some
identifier to indicate the called party, and the user terminal equipment
may lack the capability to determine the actual emergency address service URL (PSAP
URI). The use of local conventions may be required as a
transition mechanism. Note: Such use complicates international
movement of the user terminal. Evolution Since relying on recognizing local
numbering conventions makes it difficult for devices to be used
outside their home context and for external devices to be
introduced into a network, protocols should use standardized
emergency service identifier or set of identifiers is preferred.

Id7. identifiers.

Id6. Emergency service identifier marking: There Signaling protocols MUST be
support for
an emergency service identifier identifiers to be used for marking the mark a call as an
emergency call.

Motivation: Marking ensures proper handling as an emergency call
by downstream elements that may not recognize, for example, a
local variant of a logical emergency address, etc. address. This marking
mechanism is assumed to be different than a QoS related to, but independent of, marking mechanism.

Id8. Emergency calls for
prioritized call handling [10].

Id7. Handling unrecognized emergency service identifier not recognized: identifiers: There MUST
be support for calls which are initiated as emergency calls even
if the specific emergency service requested is not recognized, based
on recognized by
the ESRP. Such calls will then be routed to a generic emergency service identifier used.
service.

Motivation: In order Fallback routing allows new emergency services to have a robust system that supports
incremental service deployment be
introduced incrementally, while still maintaining avoiding non-routable emergency
calls. For example, a call for marine rescue services would be
routed to a general PSAP if the caller's location does not offer
marine rescue services yet.

Id8. Return fallback
capability. service identifier: The mapping protocol must
be able to report back the actual service mapped if the mapping
protocol substitutes another service for the one requested.

Motivation: A mapping server may be configured to automatically
look up the PSAP for another service if the user-requested service
is not available for that location. For example, if there is no
marine rescue service, the mapping protocol might return the PSAP
URL for general emergencies and include the "urn:service.sos"
identifier in the response to alert the querier to that fact.

Id9. Discovery of visited emergency dial strings: There MUST be
support for a
mechanism to allow the end device to learn visited emergency dial strings.
numbers.

Motivation: Scenarios exist where a user dials Travelers visiting a visited emergency
dial string that is different from foreign country may observe the home
local emergency dial string:
If a user (i.e., UA operator) visits a foreign country, observes a
fire truck with 999 number, e.g., seeing it painted on the side, the expectation is one side of being a
fire truck, and then rightfully expect to be able to dial that same number to summon a fire truck. Another use
case cited is where a tourist collapses, and
emergency number. Similarly, a local "good Samaritan"
uses the may use a
tourist's cell phone to enter a home emergency dial
string appropriate for that foreign country.

7. summon help.

8. Mapping Protocol

There are two basic approaches to invoke the mapping protocol. We
refer to these as caller-based and mediated. In each case, the
mapping client initiates a request to a mapping server via a mapping
protocol. A proposed mapping protocol protocol, LoST, is outlined in the document
I-D.hardie-ecrit-lost [9]. [13].

For caller-based resolution, the caller's user agent invokes the
mapping protocol to determine the appropriate PSAP based on the
location provided. The resolution may take place well before the
actual emergency call is placed, or at the time of the call.

For mediated resolution, an emergency call routing support entity,
such as a SIP (outbound) proxy or redirect server invokes the mapping
service.

Since servers may be used as outbound proxy servers by clients that
are not in the same geographic area as the proxy server, any proxy
server has to be able to translate any caller location to the
appropriate PSAP. (A traveler may, for example, accidentally or
intentionally configure its home proxy server as its outbound proxy
server, even while far away from home.)

Ma1. Baseline query protocol: A mandatory-to-implement protocol MUST
be specified.

Motivation: An over-abundance of similarly-capable choices appears
undesirable for interoperability.

Ma2. Extensible protocol: The mapping protocol MUST be designed to
support the extensibility of location data elements, both for new
and existing fields.

Motivation: This is needed, for example, to accommodate future
extensions to location information that might be included in the
PIDF-LO ([6]). ([9]).

Ma3. Incrementally deployable: The mapping protocol MUST be designed
in such a way that supports the
to support its incremental deployment of mapping
services. deployment.

Motivation: It must not be necessary, for example, to have a
global street level database before deploying the system. It is
acceptable to have some misrouting of calls when the database does
not (yet) contain accurate PSAP service area information.

Ma4. Any time mapping: The mapping protocol MUST support the ability
of the mapping function to be invoked at any time, including while
an emergency call is in process and before an emergency call is
initiated.

Motivation: Used as a fallback mechanism only, if a mapping query
fails at emergency call time, it may be advantageous to have prior
knowledge of the PSAP URI. This prior knowledge would be obtained
by performing a mapping query at any time prior to an emergency
call.

Ma5. Anywhere mapping: The mapping protocol MUST support the ability
to provide mapping information in response to an individual query
from any (earthly) location, regardless of where the mapping
client is located, either geographically or by network location.

Motivation: The mapping client, such as an ESRP, may not
necessarily be anywhere close to the caller or the appropriate
PSAP, but must still be able to obtain mapping information.

Ma6. Appropriate PSAP: The mapping protocol MUST support the routing
of an emergency call to the PSAP responsible for a particular
geographic area.

Motivation: Routing to the wrong PSAP will result in delays in
handling emergencies as calls are redirected, and therefore will
also result in inefficient use of PSAP resources at the initial
point of contact. It is important that the location determination
mechanism not be fooled by the location of IP telephony gateways
or dial-in lines into a corporate LAN (and dispatch emergency help
to the gateway or campus, rather than the caller), multi-site LANs
and similar arrangements.

Ma7. Multiple PSAP URIs: The mapping protocol MUST support a method
to return multiple PSAP URIs which cover the same geographic area.

Motivation: Two Different contact protocols (e.g., PSTN via tel URIs
and IP via SIP URIs) may be routed to different mapping servers PSAPs. Less
likely, two PSAPs may cover the same
geographic area, and therefore have the same set of overlap in their coverage
information. region.

Ma8. Single primary URI per contact protocol: Though the mapping
protocol supports may be able to include multiple URIs being returned, in the response, it
SHOULD return only one primary URI per contact protocol used, so
that clients are not required to select among different targets
for the same contact protocol.

Motivation: There may be two or more URIs returned when multiple
contact protocols are available (e.g., SIP and SMS). The client
may select among multiple contact protocols based on its
capabilities, preference settings, or availability.

Ma9. URI alternate contact: In addition to returning a primary
contact, the mapping protocol MUST support the return of a PSAP
URI or contact method explicitly marked as an alternate contact
for use when a fallback contact is needed.

Motivation: In response There may be multiple ways to a mapping request, provide addresses of
backup PSAPs, including the mapping server
will also return an alternate URI. Implementation details to be
described within an operational document. protocol, DNS lookup via NAPTR
and SRV, or call routing by SIP proxies.

Ma10. Non-preferred URI schemes: The mapping protocol MAY support
the return of a less preferred URI scheme, (e.g., TEL URI). such as a tel URI.

Motivation: In order to provide incremental support to non-IP
PSAPs it may be necessary to be able to complete an emergency call
via the PSTN.

Ma11. URI properties: The mapping protocol MUST support the ability
to provide ancillary information about a contact that allows the
mapping client to determine relevant properties of the PSAP URI.

Motivation: In some cases, the same geographic area is served by
several PSAPs, for example, a corporate campus might be served by
both a corporate security department and the municipal PSAP. The
mapping protocol should then return URIs for both, with
information allowing the querying entity to choose one or the
other. This determination could be made by either an ESRP, based
on local policy, or by direct user choice, in the case of caller-
based methods.

Ma12. Mapping referral: The mapping protocol MUST support a
mechanism for the mapping client to contact any mapping server and
be referred to another mapping server that is more qualified to
answer the query.

Motivation: To Referrals help avoid mitigate the case impact of relying on incorrect
configuration data which may cause calls that directs a client to fail, particularly for
caller-based the wrong initial mapping queries.
server.

Ma13. Split responsibility: The mapping protocol MUST support the
division of data subset handling between multiple mapping servers
within a single level of a civic location hierarchy.

Motivation: For example, two mapping servers for the same city or
county may handle different streets within that city or county.

Ma14. URL for error reporting: The mapping protocol MUST support the
ability to return a URL that can be used to report a suspected or
known error within the mapping database.

Motivation: If an error is returned, for example, there needs to
be a URL which points to a resource which can explain or
potentially help resolve the error.

Ma15. Resiliance to failure: The mapping protocol MUST support a
mechanism which enables the client to fail over to different
(replica) mapping
server in order to obtain and return a successful mapping to the
mapping client. server.

Motivation: It is important that the The failure of a single mapping server does should not preclude
the mapping client's ability to receive
mapping client from a different mapping server. receiving an answer to its query.

Ma16. Traceable resolution: The mapping protocol SHOULD support the
ability of the mapping client to be able to determine the entity
or entities that provided the emergency address resolution
information.

Motivation: It To improve reliability and performance, it is
important for public safety reasons, that there
is a method to provide operational traceability in case be able to trace which servers contributed to the
resolution of errors. a query.

Ma17. Minimal additional delay: Mapping protocol execution SHOULD
minimize the amount of delay within the overall call-setup time.

Motivation: Since outbound proxies will likely be asked to
resolve the same geographic coordinates repeatedly, a suitable time-
limited
time-limited caching mechanism should be supported.

Ma18. Alternate mapping sources: The mapping protocol MUST implement
a mechanism that allows for the retrieval of mapping information
from different sources.

Motivation: This provides the possibility of having available
alternative sources of mapping information when the normal source
is unavailable or unreachable.

Ma19. Freshness indication: The mapping protocol SHOULD support an
indicator describing how current the information provided by the
mapping source is.

9. Security Considerations

Threats and security requirements are discussed in a separate
document, see I-D.ietf-ecrit-security-threats [7] .

9.
document [11].

10. IANA Considerations

This document does not require actions by the IANA.

10.

11. Contributors

The information contained in this document is a result of a several
original joint contributions of text, which was then discussed and
refined by those and many others within the working group. These
contributors to the early text include, Nadine Abbott, Hideki Arai,
Martin Dawson, Motoharu Kawanishi, Brian Rosen, Richard Stastny,
Martin Thomson, James Winterbottom.

The contributors can be reached at:

Nadine Abbott nabbott@telcordia.com

Hideki Arai arai859@oki.com

Martin Dawson Martin.Dawson@andrew.com

Motoharu Kawanishi kawanishi381@oki.com

Brian Rosen br@brianrosen.net

Richard Stastny Richard.Stastny@oefeg.at

Martin Thomson Martin.Thomson@andrew.com

James Winterbottom James.Winterbottom@andrew.com

11.

12. Acknowledgments

In addition to thanking those listed above, we would like to also
thank Guy Caron, Barry Dingle, Keith Drage, Tim Dunn, Patrik
Faeltstroem,
Faltstrom, Clive D.W. Feather, Raymond Forbes, Randall Gellens,
Michael Haberler, Michael Hammer, Ted Hardie, Gunnar Hellstrom,
Cullen Jennings, Marc Linsner, Rohan Mahy, Patti McCalmont, Don
Mitchell, John Morris, Andrew Newton, Steve Norreys, Jon Peterson,
James Polk, Benny Rodrig, John Rosenberg, Jonathan Rosenberg, John
Schnizlein, Shida Schubert, James Seng, Byron Smith, Tom Taylor, Barbara Stark,
Tom Taylor, Hannes Tschofenig, and Nate Wilcox, Wilcox for their
invaluable helpful
input.

12.

13. References

12.1.

13.1 Normative References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

12.2.

13.2 Informative References

[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.

[3] Charlton, N., Gasson, M., Gybels, G., Spanner, M., and A. van
Wijk, "User Requirements for the Session Initiation Protocol
(SIP) in Support of Deaf, Hard of Hearing and Speech-impaired
Individuals", RFC 3351, August 2002.

[3]

[4] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004.

[4]

[5] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location
Configuration Information", RFC 3825, July 2004.

[5]

[6] Peterson, J., "Common Profile for Instant Messaging (CPIM)",
RFC 3860, August 2004.

[7] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004.

[8] Hellstrom, G. and P. Jones, "RTP Payload for Text
Conversation", RFC 4103, June 2005.

[6]

[9] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.

[7]

[10] Schulzrinne, H. and J. Polk, "Communications Resource Priority
for the Session Initiation Protocol (SIP)", RFC 4412,
February 2006.

[11] Taylor, T., "Security Threats and Requirements for Emergency
Call Marking and Mapping", draft-ietf-ecrit-security-threats-01 draft-ietf-ecrit-security-threats-03
(work in progress), April July 2006.

[8]

[12] Schulzrinne, H., "A Uniform Resource Name (URN) for Services",
draft-ietf-ecrit-service-urn-03 (work in progress), May 2006.

[9]

[13] Hardie, T., "LoST: A Location-to-Service Translation Protocol",
draft-hardie-ecrit-lost-00 (work in progress), March 2006.

[10]

[14] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4
and DHCPv6) Option for Civic Addresses Configuration
Information", draft-ietf-geopriv-dhcp-civil-09 (work in
progress), January 2006.

[11]

[15] Wijk, A., A. and G. Gybels, "Framework for real-time text over IP
using SIP",
draft-ietf-sipping-toip-04 the Session Initiation Protocol (SIP)",
draft-ietf-sipping-toip-05 (work in progress), March June 2006.

[16] Institute of Electrical and Electronics Engineers, "Station and
Media Access Control Connectivity Discovery", IEEE Standard
802.1 AB, April 2005.

Authors' Addresses

Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US

Phone: +1 212 939 7004
Email: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.edu

Roger Marshall (editor)
TeleCommunication Systems
2401 Elliott Avenue
2nd Floor
Seattle, WA 98121
US

Phone: +1 206 792 2424
Email: rmarshall@telecomsys.com
URI: http://www.telecomsys.com

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