draft-ietf-ecrit-requirements-00.txt   draft-ietf-ecrit-requirements-01.txt 
ecrit H. Schulzrinne ecrit H. Schulzrinne
Internet-Draft Columbia U. Internet-Draft Columbia U.
Expires: March 6, 2006 R. Marshall, Ed. Expires: April 24, 2006 R. Marshall, Ed.
TCS TCS
September 2, 2005 October 21, 2005
Requirements for Emergency Context Resolution with Internet Technologies Requirements for Emergency Context Resolution with Internet Technologies
draft-ietf-ecrit-requirements-00.txt draft-ietf-ecrit-requirements-01.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
This document enumerates requirements for emergency calls placed by This document enumerates requirements for emergency calls placed by
the public using voice-over-IP (VoIP) and general Internet multimedia the public using voice-over-IP (VoIP) and general Internet multimedia
systems, where Internet protocols are used end-to-end. systems, where Internet protocols are used end-to-end.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. High-Level Requirements . . . . . . . . . . . . . . . . . . . 10 4. High-Level Requirements . . . . . . . . . . . . . . . . . . . 10
5. Identifying the Caller Location . . . . . . . . . . . . . . . 12 5. Identifying the Caller Location . . . . . . . . . . . . . . . 12
6. Emergency Identifier . . . . . . . . . . . . . . . . . . . . . 13 6. Emergency Identifier . . . . . . . . . . . . . . . . . . . . . 14
7. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 15 7. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 16
8. Emergency Caller Identification . . . . . . . . . . . . . . . 19 8. Security Considerations . . . . . . . . . . . . . . . . . . . 20
9. Performance and Reliability Considerations . . . . . . . . . . 20 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 21
10. Security Considerations . . . . . . . . . . . . . . . . . . . 21 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 22 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 11.1. Normative References . . . . . . . . . . . . . . . . . . 23
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24 11.2. Informative References . . . . . . . . . . . . . . . . . 23
13.1. Normative References . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
13.2. Informative References . . . . . . . . . . . . . . . . . 24 Intellectual Property and Copyright Statements . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
Intellectual Property and Copyright Statements . . . . . . . . . . 26
1. Introduction 1. Introduction
Users of voice-centric, (telephone-like) IP-based services expect to Users of both voice-centric (telephone-like) and non voice type
be able to call for emergency help, such as police, the fire services (e.g. text messaging for hearing disabled users, (RFC 3351
department, or ambulance services, regardless of where they are, what [4]) have an expectation to be able to initiate a request for help in
(if any) service provider they are using, or what type of device they case of an emergency.
have.
Additionally, users of other real-time and near real-time services
(those other than voice) also expect to be able to summon emergency
help. For example, instant messaging (IM) and real time text users
want to have access to the same types of emergency services as
mentioned above. IM and real time text are particularly helpful for
hearing-disabled users, (RFC 3351 [4]), when there is a need for
exactness as for example for spelling out names and addresses and in
cases where bandwidth is scarce.
Unfortunately, the mechanisms for emergency calls that have evolved Unfortunately, the existing mechanisms to support emergency calls
in the public circuit-switched telephone network (PSTN) are not quite that have evolved within the public circuit-switched telephone
appropriate for evolving IP-based voice, text and real-time network (PSTN), are not appropriate to handle evolving IP-based
multimedia communications. This document outlines the key voice, text and real-time multimedia communications. This document
requirements that end systems and network elements such as SIP outlines the key requirements that IP-based end systems and network
proxies need to satisfy in order to provide emergency call services elements, such as SIP proxies, need to satisfy in order to provide
which at a minimum, offer the same functionality as existing PSTN emergency call services, which at a minimum, offer the same
services, with the goal of making emergency calling more robust, functionality as existing PSTN services, with the additional overall
less-costly to implement, and multimedia-capable. 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 This document only focuses on end-to-end IP-based calls, i.e., where
the emergency call originates from an IP end system, (Internet the emergency call originates from an IP end system, (Internet
device), and terminates to an IP-capable PSAP, done entirely over an device), and terminates to an IP-capable PSAP, done entirely over an
IP network. IP network.
This document outlines the various functional issues which relate to This document outlines the various functional issues which relate to
making an IP-based emergency call, including a description of general making an IP-based emergency call, including a description of
requirements, (Section 4), identification of the emergency caller's baseline requirements, (Section 4), identification of the emergency
location, (Section 5), use of an emergency identifier to declare a caller's location, (Section 5), use of an emergency identifier to
call to be an emergency call, (Section 6), the mapping function declare a call to be an emergency call, (Section 6), and finally, the
required to route the call to the appropriate PSAP, (Section 7), and mapping function required to route the call to the appropriate PSAP,
finally, identifying who placed the call, (Section 8) (Section 7).
Note that location is required for two separate purposes, first, to Identification of the caller, while not incompatible with the
route the call to the appropriate PSAP and second, to display the requirements for messaging outlined within this document, is not
caller's location to the call taker for help in dispatching emergency currently considered within the scope of the ECRIT charter, and is
therefore, left for a future draft to describe.
Note: Location is required for two separate purposes, first, to route
the call to the appropriate PSAP and second, to display the caller's
location to the call taker for help in dispatching emergency
assistance to the correct location. assistance to the correct location.
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
indicate requirement levels for compliant implementations. indicate requirement levels for compliant implementations.
Since a requirements document does not directly specify a protocol to Since a requirements document does not directly specify a protocol to
implement, these compliance labels should be read as indicating implement, these compliance labels should be read as indicating
requirements for the protocol or architecture, rather than an requirements for the protocol or architecture, rather than an
implementation. implementation.
For lack of a better term, we will use the term "caller" or For lack of a better term, we will use the term "caller" or
"emergency caller" to refer to the person placing an emergency call "emergency caller" to refer to the person placing an emergency call
or sending an emergency IM. or sending an emergency IM.
Access Infrastructure Provider (AIP): An organization that provides Application Service Provider (ASP): The organization or entity that
physical network connectivity to its customers or users, e.g. provides application-layer services, which may include voice (see
through digital subscriber lines, cable TV plants, Ethernet, term Voice Service Provider). This entity can be a private
leased lines or radio frequencies. This entity may or may not individual, an enterprise, a government, or a service provider.
also provide IP routing, IP addresses, or other Internet protocol An ASP is defined as something more general than a Voice Service
services. Examples of such organizations include Provider, since emergency calls are sometimes likely to use other
telecommunication carriers, municipal utilities, larger media, including text and video. Note: For a particular user, the
enterprises with their own network infrastructure, and government ASP may or may not be the same organization as the IAP and/or ISP.
organizations such as the military.
address: A description of a location of a person, organization, or
building, most often consisting of numerical and text elements
such as street number, street name, and city arranged in a
particular format.
Application Service (Voice) Provider (ASP, VSP): The organization
that provides voice or other application-layer services, such as
call routing, a SIP URI or PSTN termination. This organization
can be a private individual, an enterprise, a government or a
service provider. We avoid the term voice service provider, since
emergency calls are sometimes likely to use other media, including
text and video. For a particular user, the ASP may not be the
same organization as the AIP or ISP.
Basic Emergency Service: Basic Emergency Service allows a user to Basic Emergency Service: Basic Emergency Service allows a user to
reach a PSAP serving its current location, but the PSAP may not be reach a PSAP serving its current location, but the PSAP may not be
able to determine the identity or geographic location of the able to determine the identity or geographic location of the
caller (except by having the call taker ask the caller). caller (except by having the call taker ask the caller).
call taker: A call taker is an agent at the PSAP that accepts calls call taker: A call taker is an agent at the PSAP that accepts calls
and may dispatch emergency help. (Sometimes the functions of call and may dispatch emergency help. (Sometimes the functions of call
taking and dispatching are handled by different groups of people, taking and dispatching are handled by different groups of people,
but these divisions of labor are not generally visible to the but these divisions of labor are not generally visible to the
outside and thus do not concern us here.) outside and thus do not concern us here.)
civic location: A described location based on some defined grid, such civic location: A described location based on some defined grid, such
as a jurisdictional, postal, metropolitan, or rural reference as a jurisdictional, postal, metropolitan, or rural reference
system (e.g. street address). system (e.g. street address).
directory service: A network service which uses a distributed
directory protocol to provide information about the PSAP, or
intermediary which knows about the PSAP, and is used to assist in
routing an emergency call.
emergency address: The sip:uri, sips:uri, or tel:uri which represents emergency address: The sip:uri, sips:uri, or tel:uri which represents
the network address of the PSAP useful for the completion of a the address of the PSAP useful for the completion of an emergency
VoIP emergency call. call.
emergency caller: The user or user device entity which sends his/her emergency caller: The user or user device entity which sends his/her
location to another entity in the network. location to another entity in the network.
emergency identifier: The numerical and/or text identifier which is emergency identifier: The numerical and/or text identifier which is
supplied by a user or a user device, which identifies the call as supplied by a user or a user device, which identifies the call as
an emergency call and is translated into an emergency address for an emergency call and is translated into an emergency address for
call routing and completion. call routing and completion.
enhanced emergency service: Enhanced emergency services add the enhanced emergency service: Enhanced emergency services add the
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ESRP (Emergency Services Routing Proxy): An ESRP is a call routing ESRP (Emergency Services Routing Proxy): An ESRP is a call routing
entity that invokes the location-to-URL mapping, which in turn may entity that invokes the location-to-URL mapping, which in turn may
return either the URL for another ESRP or the PSAP. (In a SIP return either the URL for another ESRP or the PSAP. (In a SIP
system, the ESRP would typically be a SIP proxy, but could also be system, the ESRP would typically be a SIP proxy, but could also be
a Back-to-back user agent (B2BUA). a Back-to-back user agent (B2BUA).
geographic location: A reference to a locatable point described by a geographic location: A reference to a locatable point described by a
set of defined coordinates within a geographic coordinate system, set of defined coordinates within a geographic coordinate system,
(e.g. lat/lon within WGS-84 datum) (e.g. lat/lon within WGS-84 datum)
Internet Attachment Provider (IAP): An organization that provides
physical network connectivity to its customers or users, e.g.
through digital subscriber lines, cable TV plants, Ethernet,
leased lines or radio frequencies. This entity may or may not
also provide IP routing, IP addresses, or other Internet protocol
services. 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 Internet Service Provider (ISP): An organization that provides IP
network-layer services to its customers or users. This entity may network-layer services to its customers or users. This entity may
or may not provide the physical-layer and layer-2 connectivity, or may not provide the physical-layer and layer-2 connectivity,
such as fiber or Ethernet. such as fiber or Ethernet.
location: A geographic identification assigned to a region or feature location: A geographic identification assigned to a region or feature
based on a specific coordinate system, or by other precise based on a specific coordinate system, or by other precise
information such as a street address. In the geocoding process, information such as a street number and name. In the geocoding
the location is defined with an x,y coordinate value according to process, the location is defined with an x,y coordinate value
the distance north or south of the equator and east or west of the according to the distance north or south of the equator and east
prime meridian. or west of the prime meridian.
location validation: A caller location is considered valid if the location validation: A caller location is considered valid if the
civic or geographic location is recognizable within an acceptable civic or geographic location is recognizable within an acceptable
location reference systems (e.g. USPS, WGS84, etc.), and can be location reference systems (e.g. USPS, WGS-84, etc.), and can be
mapped to one or more PSAPs. Location validation ensures that a mapped to one or more PSAPs. Location validation ensures that a
location is reference able, but makes no assumption about the location is able to be referenced for mapping, but makes no
association between the caller and the caller's location. assumption about the association between the caller and the
caller's location.
Mapping: Process of resolving an address to a URI (or multiple URIs). Mapping: Process of resolving an location to a URI (or multiple
URIs).
Mapping Client: A Mapping Client interacts with the Mapping Server to Mapping Client: A Mapping Client interacts with the Mapping Server to
learn one or multiple URIs for a given address. learn one or multiple URIs for a given location.
Mapping Server: The Mapping Server holds information about the
address to URI mappings.
Miniumum Connectivity: A minimum set of [physical, virtual...??] Mapping Protocol: A protocol used to convey the mapping request and
connectivity between two endpoints. response.
[Ed. Send additional text.] Mapping Server: The Mapping Server holds information about the
location to URI mappings.
PSAP (Public Safety Answering Point): Physical location where PSAP (Public Safety Answering Point): Physical location where
emergency calls are received under the responsibility of a public emergency calls are received under the responsibility of a public
authority. (This terminology is used by both ETSI, in ETSI SR 002 authority. (This terminology is used by both ETSI, in ETSI SR 002
180, and NENA.) In the United Kingdom, PSAPs are called Operator 180, and NENA.) In the United Kingdom, PSAPs are called Operator
Assistance Centres, in New Zealand, Communications Centres. Assistance Centres, in New Zealand, Communications Centres.
Within this document, it is assumed, unless stated otherwise, that Within this document, it is assumed, unless stated otherwise, that
PSAP is that which supports the receipt of emergency calls over PSAP is that which supports the receipt of emergency calls over
IP. It is also assumed that the PSAP is reachable by IP-based IP. It is also assumed that the PSAP is reachable by IP-based
protocols, such as SIP for call signaling and RTP for media. protocols, such as SIP for call signaling and RTP for media.
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.
3. Basic Actors 3. Basic Actors
In order to support emergency services covering a large physical area In order to support emergency services covering a large physical area
various infrastructure elements are necessary: Access Infrastructure various infrastructure elements are necessary: Internet Attachment
Providers, Application (Voice) Service Provider, PSAPs as endpoints Providers, Application/Voice Service Providers, PSAPs as endpoints
for emergency calls, directory services or other infrastructure for emergency calls, directory services or other infrastructure
elements that assist in during the call routing and potentially many elements that assist in during the call routing and potentially many
other entities. other entities.
This section outlines which entities will be considered in the This section outlines which entities will be considered in the
routing scenarios discussed. routing scenarios discussed.
Location Location
Information +-----------------+ Information +-----------------+
|(1) |Access | +-----------+ |(1) |Internet | +-----------+
v |Infrastructure | | | v |Attachment | | |
+-----------+ |Provider | | Directory | +-----------+ |Provider | | Directory |
| | | (3) | | | | | | (3) | | Service |
| Emergency |<---+-----------------+-->| | | Emergency |<---+-----------------+-->| |
| Caller | | (2) | +-----------+ | Caller | | (2) | +-----------+
| |<---+-------+ | ^ | |<---+-------+ | ^
+-----------+ | +----|---------+------+ | +-----------+ | +----|---------+------+ |
^ | | Location | | | ^ | | Location | | |
| | | Information<-+ | | | | | Information<-+ | |
| +--+--------------+ |(8) | | (5) | +--+--------------+ |(8) | | (5)
| | +-----------v+ | | | | +-----------v+ | |
| (4) | |Emergency | | | | (4) | |Emergency | | |
+--------------+--->|Call Routing|<--+---+ +--------------+--->|Call Routing|<--+---+
| | |Support | | | | |Support | |
| | +------------+ | | | +------------+ |
| | ^ | | | ^ |
| | (6) | +----+--+ | | (6) | +----+--+
| (7) | +------->| | | (7) | +------->| |
+--------------+--------------->| PSAP | +--------------+--------------->| PSAP |
| | | | | |
|Application +----+--+ |Application/ +----+--+
|(Voice) | |Voice |
|Service | |Service |
|Provider | |Provider |
+---------------------+ +---------------------+
Figure 1: Framework Figure 1: Framework
Figure 1 shows the interaction between the entities involved in the Figure 1 shows the interaction between the entities involved in the
call. There are a number of different deployment choices, as it can call. There are a number of different deployment choices, as it can
be easily seen from the figure. The following deployment choices be easily seen from the figure. The following deployment choices
need to be highlighted: need to be highlighted:
o How is location information provided to the end host? It might o How is location information provided to the end host? It might
either be known to the end host itself (due to manual configuration either be known to the end host itself (due to manual configuration
or provided via GPS) or available via a third party. Even if or provided via GPS) or available via a third party. Even if
location information is known to the network it might be made location information is known to the network it might be made
available to the end host. Alternatively, location information is available to the end host. Alternatively, location information is
used as part of call routing and inserted by intermediaries. used as part of call routing and inserted by intermediaries.
o Is the Access Infrastructure Provider also the Application (Voice) o Is the Internet Attachment Provider also the Application/Voice
Service Provider? In the Internet today these roles are typically Service Provider? In the Internet today these roles are typically
provided by different entities. As a consequence, the Application provided by different entities. As a consequence, the Application/
(Voice) Service Provider is typically not able to learn the physical Voice Service Provider is typically not able to learn the physical
location of the Emergency Caller. location of the emergency caller.
Please note that the overlapping squares aim to indicate that certain Please note that the overlapping squares aim to indicate that certain
functionality can be collapsed into a single entity. As an example, functionality can be collapsed into a single entity. As an example,
the Application (Voice) Service Provider might be the same entity as the Application/Voice Service Provider might be the same entity as
the Access Infrastructure Provider and they might also operate the the Internet Attachment Provider and they might also operate the
PSAP. There is, however, no requirement that this must be the case. PSAP. There is, however, no requirement that this must be the case.
Additionally it is worth pointing out that end systems might be its Additionally it is worth pointing out that end systems might be its
own VSP, e.g., for enterprises or residential users. own VSP, e.g., for enterprises or residential users.
Below, we describe various interactions between the entities shown in Below, we describe various interactions between the entities shown in
Figure 1 are described: Figure 1 are described:
o (1) Location information might be available to the end host itself. o (1) Location information might be available to the end host itself.
o (2) Location information might, however, also be obtained from the o (2) Location information might, however, also be obtained from the
Access Infrastructure Provider (e.g., using DHCP or application layer Internet Attachment Provider (e.g., using DHCP or application layer
signaling protocols). signaling protocols).
o (3) The Emergency Caller might need to consult a directory to o (3) The Emergency Caller might need to consult a directory service
determine the PSAP that is appropriate for the physical location of to determine the PSAP that is appropriate for the physical location
the emergency caller (and considering other attributes such as a of the emergency caller (and considering other attributes such as a
certain language support by the Emergency Call Takers). certain language support by the Emergency Call Takers).
o (4) The Emergency Caller might get assistance for emergency call o (4) The Emergency Caller might get assistance for emergency call
routing by infrastructure elements (referred as Emergency Call routing by infrastructure elements (referred as Emergency Call
Routing Support entities). In case of SIP these entities are Routing Support entities). In case of SIP these entities are
proxies. proxies.
o (5) Individual Emergency Call Routing Support entities might need o (5) Individual Emergency Call Routing Support entities might need
to consult a directory to determine where to route the emergency to consult a directory servic to determine where to route the
call. emergency call.
o (6) The Emergency Call Routing Support entities need to finally o (6) The Emergency Call Routing Support entities need to finally
forward the call, if infrastructure based emergency call routing is forward the call, if infrastructure based emergency call routing is
used. used.
o (7) The emergency caller might interact directly with the PSAP o (7) The emergency caller might interact directly with the PSAP
without any Emergency Call Routing Support entities. without any Emergency Call Routing Support entities.
4. High-Level Requirements 4. High-Level Requirements
Below, we summarize high-level architectural requirements that guide Below, we summarize high-level architectural requirements that guide
some of the component requirements detailed later in the document. some of the component requirements detailed later in the document.
R1. Application Service Provider: The existence of an Application Re1. Application Service Provider: The existence of an Application
Service Provider (ASP) MUST NOT be assumed. Service Provider (ASP) MUST NOT be assumed.
Motivation: The caller may not have a application (voice) service Motivation: The caller may not have a application/voice service
provider. For example, a residence may have its own DNS domain provider. For example, a residence may have its own DNS domain
and run its own SIP proxy server for that domain. On a larger and run its own SIP proxy server for that domain. On a larger
scale, a university might provide voice services to its students scale, a university might provide voice services to its students
and staff, but not be a telecommunication provider. and staff, but not be a telecommunication provider.
R2. International: The protocols and protocol extensions developed Re2. International: The protocols and protocol extensions developed
MUST support regional, political and organizational differences. MUST support regional, political and organizational differences.
Motivation: It must be possible for a device or software developed Motivation: It must be possible for a device or software developed
or purchased in one country to place emergency calls in another or purchased in one country to place emergency calls in another
country. System components should not be biased towards a country. System components should not be biased towards a
particular set of emergency numbers or languages. Also, different particular set of emergency numbers or languages. Also, different
countries have evolved different ways of organizing emergency countries have evolved different ways of organizing emergency
services, e.g. either centralizing them or having smaller regional services, e.g. either centralizing them or having smaller regional
subdivisions such as United States counties or municipalities subdivisions such as United States counties or municipalities
handle emergency calls. handle emergency calls.
R3. Distributed Administration: Deployment of emergency services Re3. Distributed Administration: Deployment of emergency services
MUST NOT depend on a sole central administration authority. MUST NOT depend on a sole central administration authority.
Motivation: Once common standards are established, it must be Motivation: Once common standards are established, it must be
possible to deploy and administer emergency calling features on a possible to deploy and administer emergency calling features on a
regional or national basis without requiring coordination with regional or national basis without requiring coordination with
other regions or nations. The system cannot assume, for example, other regions or nations. The system cannot assume, for example,
that there is a single global entity issuing certificates for that there is a single global entity issuing certificates for
PSAPs, ASPs, AIPs or other participants. PSAPs, ASPs, IAPs or other participants.
R4. Multiple Modes: Multiple communication modes, such as audio, Re4. Multiple Modes: Multiple communication modes, such as audio,
video and text messaging MUST be supported. video and text messaging MUST be supported.
Motivation: In PSTN, voice and text telephony (often called TTY or Motivation: In PSTN, voice and text telephony (often called TTY or
textphone in North America ) are the only commonly supported textphone in North America ) are the only commonly supported
media. Emergency calling must support a variety of media. Such media. Emergency calling must support a variety of media. Such
media should include voice, conversational text (RFC 4103 [6]), media should include voice, conversational text (RFC 4103 [6]),
instant messaging and video. instant messaging and video.
R5. Minimum Connectivity: An emergency call SHOULD succeed as long Re5. Alternate Mapping Sources: The mapping protocol SHOULD allow
as there is a working network path between the caller and the for alternative redundant sources of mapping information, possibly
PSAP. In particular, reliance during call set-up and calls on of different degrees of currency.
entities and network paths that are located elsewhere should be
minimized.
Example: A caller in New York who needs to contact a PSAP in the
same city shouldn't have to get information from some entity in
Texas to make that call, as the call would then fail if the New
York to Texas path is unavailable. (To avoid this, the caller
could, for example, have cached mapping information, use a local
server that has the necessary information, or use other mechanisms
to avoid such off-path dependencies.)
[Ed. Added a skeleton definintion of "minimum connectivity" to Motivation: This provides the possibility of having available
terms section (per ietf63 ecrit meeting minutes note), but still alternative sources of mapping information when the normal source
no resolution for the above.] is unavailable or unreachable, without specifying the means by
which the alternative source is created or updated.
R6. Incremental Deployment: The ECRIT mapping protocol MUST return Re6. Incremental Deployment: The ECRIT mapping protocol MUST return
URIs that are useable by a standard signaling protocol (i.e., URIs that are usable by a standard signaling protocol (i.e.,
without special emergency extensions) unless an error is returned. without special emergency extensions) unless an error is returned.
Motivation: The format of the output returned by the mapping Motivation: The format of the output returned by the mapping
protocol is in a standard format for communication protocol. For protocol is in a standard format for communication protocol. For
example, it should return something SIP specific (e.g. URI), that example, it should return something SIP specific (e.g. URI), that
any SIP capable phone would be able to use if used in a SIP any SIP capable phone would be able to use if used in a SIP
context. Special purpose URIs would not be understood by "legacy" context. Special purpose URIs would not be understood by "legacy"
SIP devices since they do not have knowledge about the mapping SIP devices since they do not have knowledge about the mapping
protocol, and therefore are not to be used. protocol, and therefore are not to be used.
R7. Relay Services: It SHOULD be possible to involve relay services Re7. Relay Services: It SHOULD be possible to involve relay
in the call for translation between different modes. services in the call for translation between different modes.
Motivation: It should be possible to connect the relay service so Motivation: It should be possible to connect the relay service so
that the direct flow of media to the emergency service is that the direct flow of media to the emergency service is
maintained. In addition, it should be possible to convey maintained. In addition, it should be possible to convey
telemetry data, such as data from automobile crash sensors. telemetry data, such as data from automobile crash sensors.
D1. PSAP Identification: The mapping information MUST be available Re8. PSAP Identification: The mapping information MUST be available
without having to enroll with a service provider. without having to enroll with a service provider.
Motivation: The mapping server may well be operated by a service Motivation: The mapping server may well be operated by a service
provider, but access to the server offering the mapping must not provider, but access to the server offering the mapping must not
require use of a specific ISP or VSP. require use of a specific ISP or VSP.
5. Identifying the Caller Location 5. Identifying the Caller Location
Location can either be provided directly, or by reference, and Location can either be provided directly, or by reference, and
represents either a civic location, or as a geographic location. How represents either a civic location, or as a geographic location. How
skipping to change at page 12, line 25 skipping to change at page 12, line 25
announcements (LLDP). announcements (LLDP).
UA-referenced: The caller's user agent provides a reference, via a UA-referenced: The caller's user agent provides a reference, via a
permanent or temporary identifier, to the location which is stored permanent or temporary identifier, to the location which is stored
by a location service somewhere else and then retrieved by the by a location service somewhere else and then retrieved by the
PSAP. PSAP.
Proxy-inserted: A proxy along the call path inserts the location or Proxy-inserted: A proxy along the call path inserts the location or
location reference. location reference.
L6. Validation of civic location: It MUST be possible to validate an Lo1. Validation of civic location: It MUST be possible to validate
address prior to its use in an actual emergency call. an civic location prior to its use in an actual emergency call.
Motivation: Location validation refers to a process to determine Motivation: Location validation provides an opportunity to help
whether or not a given civic location is valid or not. assure ahead of time, whether 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.
L10. Preferred datum: The preferred coordinate reference system for Lo2.: Validation of a civic location MUST NOT be required to enable
emergency calls MUST be WGS-84. any feature that is part of the emergency call process.
L28. Location Provided: An Emergency Services Routing Proxy (ESRP) Motivation: In some cases, (based on a variety of factors), 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 signaling path to the PSAP.
Lo3. Reference Datum: The mapping server MUST understand WGS-84
coordinate reference system and may understand other reference
systems.
Lo4. Location Provided: An Emergency Services Routing Proxy (ESRP)
MUST NOT remove location information after performing location MUST NOT remove location information after performing location
based routing. based routing.
Motivation: The ESRP and the PSAP use the same location Motivation: The ESRP and the PSAP use the same location
information object but for a different purpose. Therefore, the information object but for a different purpose. Therefore, the
PSAP still requires the receipt of information which represents PSAP still requires the receipt of information which represents
the end device's location. the end device's location.
L29.: Validation of civic addresses MUST NOT be required to enable
any feature that is part of the emergency call process.
Motivation: Emergency routing protocols must take into account
location based on a variety of forms and formats, (e.g. civic
address, MSAG, USPS, lat/lon, etc.) and be able to perform
adequate PSAP routing for the context in which the call is
initiated.
6. Emergency Identifier 6. Emergency Identifier
A1a. Universal Identifier - Setup: One or more universal emergency Id1. Universal Identifier - Setup: One or more universal emergency
identifiers MUST be recognized by any device or network element identifiers MUST be recognized by any device or network element
for call setup purposes for call setup purposes
Motivation: There must be some way for any device or element to Motivation: There must be some way for any device or element to
recognize an emergency call throughout the call setup. This is recognize an emergency call throughout the call setup. This is
regardless of the device location, the application (voice) service regardless of the device location, the application (voice) service
provider used (if any at all), or of any other factor. Examples provider used (if any at all), or of any other factor. Examples
of these might include: 911, 112, and sos.*. of these might include: 911, 112, and sos.*.
A1b. Universal Identifier - Mapping: One or more universal emergency Id2. Universal Identifier Resolution: Where multiple emergency
identifiers MUST be recognized by any device or network element to service types exist, it MUST be possible to treat each emergency
support mapping. identifier separately, based on the specific type of emergency
help requested.
Motivation: Mapping must be made to work under all circumstances, Motivation: Some jurisdictions may have multiple types of
by any network element or device. This is regardless of the emergency services available at the same level, (e.g. fire,
device location, the application (voice) service provider used (if police, ambulance), in which case it is important that any one
any at all), or of any other factor. Examples of these might could be selected directly.
include: 911, 112, and sos.*.
A1c. Emergency Marking: Emergency requests which are not already Id3. Emergency Marking: Any device in the signaling path that
marked as emergency calls, MUST be recognizable and marked by user recognizes by some means that the signaling is associated with an
agents, proxies, and other network elements as emergency calls. emergency call MUST add the emergency indication called for in A1a
to the signaling before forwarding it. This marking mechanism
must be different than QoS marking.
Motivation: SIP and other call signaling protocols are not Motivation: Marking ensures proper handling as an emergency call
specific to one country or service provider and devices are likely by downstream elements that may not recognize, for example, a
to be used across national or service provider boundaries. Since local variant of a logical emergency address (see requirement
services such as disabling mandatory authentication for emergency A4+).
calls requires the cooperation of outbound proxies, the outbound
proxy has to be able to recognize the emergency address and be
assured that it will be routed as an emergency call. A universal
address also makes it possible to create user interface elements
that are correctly configured without user intervention. UA
features could be made to work without such an identifier, but the
user interface would then have to provide an unambiguous way to
declare a particular call an emergency call.
A3. Recognizable: Emergency calls MUST be recognizable by user Id4. Emergency Identifier-based Marking: User agents, proxies, and
agents, proxies and other network elements. other network elements that process signaling associated with
emergency calls SHOULD be configured to recognize a reasonable
selection of logical emergency identifiers (described in
requirements below) as a means to initiate emergency marking.
Motivation: To prevent fraud, an address identified as an Motivation: Since user devices roam, emergency identifiers may
emergency number for call features or authentication override MUST vary from region to region. It is therefore important that a
also cause routing to a PSAP. network entity be able to perform mapping and/or call routing
within the context of its own point of origin rather than relying
on non-local logical emergency identifiers as the only basis for
emergency marking of calls.
A4. Minimal configuration: Any local emergency identifiers SHOULD be Id5. Prevention of Fraud: A call identified as an emergency call or
configured automatically, without user intervention. marked as such in accordance with the above requirements for
marking MUST be routed to a PSAP.
Motivation: this prevents use of the emergency call indication to
gain access to call features or authentication override for non-
emergency purposes.
Id6. Minimal configuration: Any local emergency identifiers SHOULD
be configured automatically, without user intervention.
Motivation: A new UA "unofficially imported" into an organization Motivation: A new UA "unofficially imported" into an organization
from elsewhere should have the same emergency capabilities as one from elsewhere should have the same emergency capabilities as one
officially installed. officially installed.
7. Mapping Protocol Id7. Emergency Identifier Replacement: For each signaling protocol
that can be used in an emergency call, reserved identifiers SHOULD
be allowed to replace the original emergency identifier, based on
local conventions, regulations, or preference (e.g. as in the case
of an enterprise).
There are two approaches for triggering the mapping protocol: caller- Motivation: Any signalling protocol requires the use of some
based, or mediated. identifier to indicate the called party, and the user terminal may
lack the capability to determine the actual emergency address
(PSAP uri). The use of local conventions may be required as a
transition mechanism. Note: Such use complicates international
movement of the user terminal, and evolution to a standardized
universal emergency identifier or set of identifiers is preferred.
From the previous section, we take the requirement of a single (or a 7. Mapping Protocol
small number of) emergency addresses which are independent of the
caller's location. However, since for reasons of robustness,
jurisdictional and local knowledge, and since PSAPs only serve a
limited geographic region, having the call reach the appropriate PSAP
is crucial.
There appears to be two basic architectures for translating an Given the requirement from the previous section, that of a single (or
small number of) emergency identifier(s) which are independent of the
caller's location, and since PSAPs only serve a limited geographic
region, and for reasons of jurisdictional and local knowledge, having
the call reach the appropriate PSAP based on a mapping protocol, is
crucial.
There are two basic architectures described for translating an
emergency identifier into the appropriate PSAP emergency address. We emergency identifier into the appropriate PSAP emergency address. We
refer to these as caller-based and mediated. In caller-based refer to these as caller-based and mediated.
resolution, the caller's user agent consults a directory and
determines the appropriate PSAP based on its location. For caller-based resolution, the caller's user agent consults a
mapping service 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, a call signaling server, such as a SIP For mediated resolution, a call signaling server, such as a SIP
(outbound) proxy or redirect server performs this function. Note (outbound) proxy or redirect server performs this function (a request
that the latter case includes the architecture where the call is for mapping) by invoking the mapping protocol.
Note that this case relies on an architecture where the call is
effectively routed to a copy of the database, rather than having some effectively routed to a copy of the database, rather than having some
non-SIP protocol query the database. Since servers may be used as non-SIP protocol query the database.
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.)
The resolution may take place well before the actual emergency call Since servers may be used as outbound proxy servers by clients that
is placed, or at the time of the call. 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.)
The problem at hand is more difficult to resolve than that for The problem at hand is more difficult to resolve than that for
traditional web or email services. In this case, the emergency traditional web or email services. In this case, the emergency
caller only dialed an emergency identifier, and depending on the caller only dialed an emergency identifier, and depending on the
location, any one of several thousand PSAPs around the world could be location, any one of several thousand PSAPs around the world could be
appropriate PSAP. In addition, the caller probably does not care appropriate PSAP. In addition, there may be a finer resolution of
which specific PSAP answers the call, but rather that it be an routing (which the caller isn't aware of), which results in a
accredited PSAP, e.g. one run by the local government authorities. particular "accredited" PSAP (i.e. one run by local authorities)
(Many PSAPs are run by private entities. For example, universities answering to call. (Many PSAPs are run by private entities. For
and corporations with large campuses often have their own emergency example, universities and corporations with large campuses often have
response centers.) their own emergency response centers.)
I1. Appropriate PSAP: Calls MUST be routed to the PSAP responsible Ma1. Appropriate PSAP: Calls MUST be routed to the PSAP responsible
for this particular geographic area. for this particular geographic area. In particular, the location
determination should 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.
Motivation: In particular, the location determination should not Motivation: Routing to the wrong PSAP will result in delays in
be fooled by the location of IP telephony gateways or dial-in handling emergencies as calls are redirected, and result in
lines into a corporate LAN (and dispatch emergency help to the inefficient use of PSAP resources at the initial point of contact.
gateway or campus, rather than the caller), multi-site LANs and
similar arrangements.
I3. Mapping redirection: The mapping protocol MUST support Ma2. Mapping redirection: The mapping protocol MUST support
redirection functionality. redirection functionality, since in some cases, an initial mapping
may provide a single URL for a large geographic area. Redirection
is needed to then re-invokes the mapping protocol on a different
database to obtain another URL for an more resolute ESRP or PSAP,
which covers a smaller area.
Motivation: In some cases, an initial mapping may provide a single Motivation: The more local the mapping output is, the more
URL for a large geographic area. The ESRP identified by that URL favourable (in most cases) the likely outcome will be for the
then re-invokes the mapping protocol on a different database to emergency caller.
obtain another URL for an ESRP or PSAP covering a smaller area.
D5. Minimal additional delay: The execution of the mapping protocol Ma3. Minimal additional delay: The execution of the mapping protocol
SHOULD minimize the amount of additional delay to the overall SHOULD minimize the amount of additional delay to the overall
call-setup time. call-setup time.
Motivation: Since outbound proxies will likely be asked to resolve Motivation: Since outbound proxies will likely be asked to resolve
the same geographic coordinates repeatedly, a suitable time- the same geographic coordinates repeatedly, a suitable time-
limited caching mechanism should be supported. limited caching mechanism should be supported.
D7. Referral: The mapping client MUST be able to contact any server Ma4. Referral: The mapping client MUST be able to contact any server
and be referred to another server that is more qualified to answer and be referred to another server that is more qualified to answer
the query. the query.
Motivation: This requirement alleviates the potential for Motivation: This requirement alleviates the potential for
incorrect configurations to cause calls to fail, particularly for incorrect configurations to cause calls to fail, particularly for
caller-based queries. caller-based queries.
I4. Return multiple PSAPs: The mapping protocol MUST be able to Ma5. The mapping protocol MUST allow a response to carry multiple
URIs.
Motivation: In response to a mapping request, a server will
normally provide a URI or set of URIs for contacting the
appropriate PSAP.
Ma6. The mapping protocol MUST be able to return a URI or contact
method explicitly marked as an alternate contact.
Motivation: In response to a mapping request, if an expected URI
is unable to be returned, then mapping server may return an
alternate URI. When and how this would be used will be described
in an operational document.
Ma7. Multiple PSAP uri's: The mapping protocol MUST be able to
return multiple URLs for different PSAPs that cover the same area. return multiple URLs for different PSAPs that cover the same area.
The mapping protocol must provide additional information that Ma8. URL properties: The mapping protocol must provide additional
allows the querying entity to determine relevant properties of the information that allows the querying entity to determine relevant
URL. properties of the URL.
Motivation: In some cases, the same geographic area is served by Motivation: In some cases, the same geographic area is served by
several PSAPs, for example, a corporate campus might be served by several PSAPs, for example, a corporate campus might be served by
both a corporate security department and the municipal PSAP. The both a corporate security department and the municipal PSAP. The
mapping protocol should then return URLs for both, with mapping protocol should then return URLs for both, with
information allowing the querying entity to choose one or the information allowing the querying entity to choose one or the
other. This determination could be made by either an ESRP, based other. This determination could be made by either an ESRP, based
on local policy, or by direct user choice, in the case of caller- on local policy, or by direct user choice, in the case of caller-
based trigger methods. based trigger methods.
I7. Traceable resolution: The entity requesting mapping SHOULD be Ma9. Traceable resolution: The entity requesting mapping SHOULD be
able to determine the entity or entities who provided the able to determine the entity or entities who provided the
emergency address resolution information. emergency address resolution information.
I8. Resilience against server failure: A client MUST be able to fail Motivation: To provide operational traceability in case of errors.
over to another replica of the mapping server, so that a failure
of a server does not endanger the ability to perform the mapping.
I10. Incrementally deployable: The mapping function MUST be capable Ma10. Resilience against server failure: A client MUST be able to
fail over to another replica of the mapping server, so that a
failure of a server does not endanger the ability to perform the
mapping.
Ma11. Incrementally deployable: The mapping function MUST be capable
of being deployed incrementally. of being deployed incrementally.
It must not be necessary, for example, to have a global street Motivation: It must not be necessary, for example, to have a
level database before deploying the system. It is acceptable to global street level database before deploying the system. It is
have some misrouting of calls when the database does not (yet) acceptable to have some misrouting of calls when the database does
contain accurate boundary information. not (yet) contain accurate boundary information.
I13. Verify mapping support: The mapping protocol SHOULD support the Ma12. Verify mapping support: The mapping protocol SHOULD support
ability for a requesting entity to verify that mapping services the ability for a requesting entity to verify that mapping
are available for a referenced location. services are available for a referenced location.
Motivation: It should be possible to make sure ahead of time, that Motivation: It should be possible to make sure ahead of time, that
requests for emergency services will work when needed. requests for emergency services will work when needed.
I25. Mapping requested from anywhere: The mapping protocol MUST be Ma13. Mapping requested from anywhere: The mapping protocol MUST be
able to provide the mapping regardless of where the mapping client able to provide the mapping regardless of where the mapping client
is located, either geographically or by network location. is located, either geographically or by network location.
Motivation: The mapping client, (such as the ESRP), may not Motivation: The mapping client, (such as the ESRP), may not
necessarily be anywhere close to the caller or the appropriate necessarily be anywhere close to the caller or the appropriate
PSAP, but must still be able to obtain a mapping. PSAP, but must still be able to obtain a mapping.
I31: The mapping protocol MUST allow a response to carry multiple Ma14. Location Updates: It SHOULD be possible to have updates of
URIs.
Motivation: In response to a mapping request, a server will
normally provide a URI or set of URIs for contacting the
appropriate PSAP.
I31b: The mapping protocol MUST be able to return a URI or contact
method explicitly marked as an alternate contact.
Motivation: In response to a mapping request, if an expected URI
is unable to be returned, then mapping server may return an
alternate URI. When and how this would be used will be described
in an operational document.
I39. Location Updates: It SHOULD be possible to have updates of
location. location.
Motivation: Updated location information may change call routing, Motivation: Updated location information may have an impact on
(some device measurement techniques provide quick (i.e. early), PSAP routing. In some cases it may be possible to redirect that
but imprecise "first fix" location). call to a more appropriate PSAP (some device measurement
techniques provide quick (i.e. early), but imprecise "first fix"
location).
I40. The mapping protocol MUST be extensible to allow for the Ma15. Extensible Protocol The mapping protocol MUST be extensible to
inclusion of new location fields. allow for the inclusion of new location fields.
Motivation: This is needed, for example, to accommodate future Motivation: This is needed, for example, to accommodate future
extensions to location information that might be included in the extensions to location information that might be included in the
PIDF-LO (I-D.ietf-geopriv-pidf-lo-03 [2]) PIDF-LO (I-D.ietf-geopriv-pidf-lo-03 [2])
I41. Split responsibility: The mapping protocol MUST allow that Ma16. Split responsibility: The mapping protocol MUST allow that
within a single level of the civic address hierarchy, multiple within a single level of the civic location hierarchy, multiple
mapping servers handle subsets of the data elements. mapping servers handle subsets of the data elements.
Motivation: For example, two directories for the same city or Motivation: For example, two directories for the same city or
county may handle different streets within that city or county. county may handle different streets within that city or county.
I42. The mapping function MUST be able to be invoked at any time, Ma17. The mapping function MUST be able to be invoked at any time,
including while an emergency call is in process. including while an emergency call is in process.
D9. Baseline query protocol: A mandatory-to-implement protocol MUST Ma18. Baseline query protocol: A mandatory-to-implement protocol
be specified. MUST be specified.
Motivation: An over-abundance of similarly-capable choices appears Motivation: An over-abundance of similarly-capable choices appears
undesirable for interoperability. undesirable for interoperability.
8. Emergency Caller Identification 8. Security Considerations
TEXT REQUESTED
[Ed. This section was never here, but was requested (H.
Schulzrinne, 8/09/05 email.).]
9. Performance and Reliability Considerations
Baseline performance and reliability requirements, while tend to be
more of an implementation related set of issues, should still be
discussed some within the context of basic requirements for the
protocol. Therefore, some suggested values relating to portions of
the routing protocol are provided.
Latency to ring-tone It is recommended that a session setup interval
be no more than 2 seconds, 68% (1-sigma) of the time, 4 seconds
for 95% (2-sigma), and 8 seconds for 99% (3-sigma), for the
interval of time between when the session is initiated, until the
time that the signaling "ring-tone" is received by the initiator.
[Ed. Not sure if the inclusion of this here is warranted. May
still be controversial.]
Latency to operator It is recommended that a session setup interval
be no more than 6 seconds, 68% (1-sigma) of the time, 8 seconds
for 95% (2-sigma), and 10 seconds for 99% (3-sigma), for the
interval of time between when the session is initiated, until the
time that the signaling is received by the operator.
[Ed. same comment as above.]
10. Security Considerations
Note: Security Considerations are referenced in the ECRIT security Note: Security Considerations are referenced in the ECRIT security
document [3]. document [3].
11. Contributors 9. Contributors
The information contained in this document is a result of a joint The information contained in this document is a result of a joint
effort based on individual contributions by those involved in the effort based on individual contributions by those involved in the
ECRIT WG. The contributors include Nadine Abbott, Hideki Arai, ECRIT WG. The contributors include Nadine Abbott, Hideki Arai,
Martin Dawson, Motoharu Kawanishi, Brian Rosen, Richard Stastny, Martin Dawson, Motoharu Kawanishi, Brian Rosen, Richard Stastny,
Martin Thomson, James Winterbottom. Martin Thomson, James Winterbottom.
The contributors can be reached at: The contributors can be reached at:
Nadine Abbott nabbott@telcordia.com Nadine Abbott nabbott@telcordia.com
Hideki Arai arai859@oki.com Hideki Arai arai859@oki.com
Martin Dawson mdawson@nortelnetworks.com Martin Dawson Martin.Dawson@andrew.com
Motoharu Kawanishi kawanishi381@oki.com Motoharu Kawanishi kawanishi381@oki.com
Brian Rosen br@brianrosen.net Brian Rosen br@brianrosen.net
Richard Stastny Richard.Stastny@oefeg.at Richard Stastny Richard.Stastny@oefeg.at
Martin Thomson marthom@nortelnetworks.com Martin Thomson Martin.Thomson@andrew.com
James Winterbottom winterb@nortelnetworks.com James Winterbottom James.Winterbottom@andrew.com
12. Acknowledgments 10. Acknowledgments
We would like to thank James Polk, Ted Hardie and Andrew Newton for We would like to thank Michael Hammer, Ted Hardie, Marc Linsner,
Andrew Newton, James Polk, Tom Taylor, and Hannes Tschofenig for
their input. their input.
13. References 11. References
13.1. Normative References 11.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Peterson, J., "A Presence-based GEOPRIV Location Object Format", [2] Peterson, J., "A Presence-based GEOPRIV Location Object Format",
draft-ietf-geopriv-pidf-lo-03 (work in progress), draft-ietf-geopriv-pidf-lo-03 (work in progress),
September 2004. September 2004.
[3] Tschofenig, H., "Security Threats and Requirements for Emergency [3] Tschofenig, H., "Security Threats and Requirements for Emergency
Calling", draft-tschofenig-ecrit-security-threats-01 (work in Calling", draft-tschofenig-ecrit-security-threats-01 (work in
progress), July 2005. progress), July 2005.
13.2. Informative References 11.2. Informative References
[4] Charlton, N., Gasson, M., Gybels, G., Spanner, M., and A. van [4] Charlton, N., Gasson, M., Gybels, G., Spanner, M., and A. van
Wijk, "User Requirements for the Session Initiation Protocol Wijk, "User Requirements for the Session Initiation Protocol
(SIP) in Support of Deaf, Hard of Hearing and Speech-impaired (SIP) in Support of Deaf, Hard of Hearing and Speech-impaired
Individuals", RFC 3351, August 2002. Individuals", RFC 3351, August 2002.
[5] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. [5] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004. Polk, "Geopriv Requirements", RFC 3693, February 2004.
[6] Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation", [6] Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation",
RFC 4103, June 2005. RFC 4103, June 2005.
[7] Wijk, A., "Framework of requirements for real-time text [7] Wijk, A., "Framework of requirements for real-time text
conversation using SIP", draft-ietf-sipping-toip-02 (work in conversation using SIP", draft-ietf-sipping-toip-03 (work in
progress), August 2005. progress), September 2005.
Authors' Addresses Authors' Addresses
Henning Schulzrinne Henning Schulzrinne
Columbia University Columbia University
Department of Computer Science Department of Computer Science
450 Computer Science Building 450 Computer Science Building
New York, NY 10027 New York, NY 10027
US US
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