WDIFF

draft-ietf-ecrit-requirements-06.txt --> draft-ietf-ecrit-requirements-07.txt

ECRIT H. Schulzrinne
Internet-Draft Columbia U.
Expires: September 7, October 21, 2006 R. Marshall, Ed.
TCS
March 6,
April 19, 2006

Requirements for Emergency Context Resolution with Internet
Technologies
draft-ietf-ecrit-requirements-06.txt
draft-ietf-ecrit-requirements-07.txt

Status of this Memo

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This Internet-Draft will expire on September 7, October 21, 2006.

Abstract

This document 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.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. High-Level Requirements . . . . . . . . . . . . . . . . . . . 12
5. Identifying the Caller's Location . . . . . . . . . . . . . . 14 15
6. Emergency Identifier . . . . . . . . . . . . . . . . . . . . . 15 18
7. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 18 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 24 25
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 25 26
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26 27
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27 28
11.1. Normative References . . . . . . . . . . . . . . . . . . 27 28
11.2. Informative References . . . . . . . . . . . . . . . . . 27 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28 29
Intellectual Property and Copyright Statements . . . . . . . . . . 29 30

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1. Introduction

Users of both voice-centric (telephone-like) and non voice type
services (e.g., text communication for hearing disabled users (RFC
3351 [8]) have an expectation 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 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 an IP-capable PSAP, conveyed entirely over an IP network.

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

Ideally, the mapping protocol would yield a URI from a preferred set
of URIs (e.g., SIP:URI, SIPS:URI) which would allow an emergency call
to be completed using IP end-to-end. Despite this goal, some PSAPs
may not immediately have IP based connectivity, and therefore it is
imperative that the URI scheme not be fixed, in order to ensure
support for a less preferred set of URIs, URIs such as as, for example, a TEL
URI which may be used to complete a 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 the ECRIT charter.

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 appropriate location.

As used in this document, validation of location does not require to

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that we ascertain as to whether or not the location actually exists.
For example, validation might only check that the house number in a
civic address falls within the assigned range, not whether that the
building exists at that spot. location. However, such higher precision
validation is desirable.

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2. 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].

Since a requirements document does not directly specify a protocol to
implement, [1],
with the qualification that unless otherwise stated these compliance labels should be read as indicating
requirements for words apply
to the protocol design of the mapping protocol, not its implementation or architecture, rather than an
implementation.
application.

Codes: "caller" or "emergency caller" refers to the person placing an
emergency call or sending an emergency instant message (IM).

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.

Basic Emergency Service: Basic Emergency Service allows a user 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 the caller.

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
outside and thus do not concern us here.

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

Emergency address: The URI (e.g., SIP:URI, SIPS:URI, XMPP:URI, IM:
URI, etc.) which represents the address of the PSAP useful for the
completion of an emergency call.

Emergency call routing support: An intermediary function which
assists in the routing of an emergency call via IP. An ESRP, ESRP is an
example of an Emergency call routing support entity.

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Emergency caller: The user or user device entity which sends his/her
location to another entity in the network.

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Emergency identifier: The numerical and/or text An identifier which is
supplied by a user or that marks a user device, which identifies the call as an emergency
call. A universal emergency identifier is an example
of an emergency identifier.

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

Enhanced emergency service: Enhanced emergency services add the
ability to identify 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.)

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

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

Internet Attachment Provider (IAP): An organization that provides
physical and 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 connectivity,
such as fiber or Ethernet, i.e., it may or may not be the role of
an IAP.

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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.

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Location-dependent emergency dial string: Location-dependent
emergency dial strings should be thought of as the digit sequence
that is dialed in order to reach emergency services. There are
two dial strings, namely either a "home emergency dial string", or
a "visited emergency dial string", and is something separate from
a universal
an emergency identifier, since each represents specific emergency
dial string key sequences which are recognized within a local
geographic area or jurisdiction.

Location validation: A caller location is considered valid if the
civic or geographic location is recognizable within an acceptable
location reference systems system (e.g., USPS, WGS-84, etc.), 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. 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.

Mapping: Process The process of resolving a location to a URI (or multiple URIs) 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
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-URI mappings.
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.

PSAP (Public Safety Answering Point): 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 the receipt of emergency calls over

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IP. It is also assumed that the PSAP is reachable by IP-based
protocols, such as SIP for call signaling and RTP for media.

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PSAP URI: PSAP URI is a general term, used to refer to the output of
the mapping protocol, and represents either the actual PSAP IP
address, or the IP address of some other intermediary, e.g., an
ESRP, which points to the actual PSAP.

Universal emergency identifier: An emergency identifier which is
recognized by any compatible endpoint, from any geographic
location. A general approach to using universal emergency
identifiers is outlined in the service URN draft (I-D.ietf-ecrit-
service-urn [5]).

Visited emergency dial string: A visited emergency dial string
represents a sequence of digits that is used to initiate an
emergency call within a geographically correct location of the
caller if outside the caller's "home" location or vicinity.

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".

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3. Basic Actors

In order to support emergency services covering a large physical
area, various infrastructure elements are necessary, including:
Internet Attachment Providers (IAPs), Application/Voice Service
Providers (ASPs or VSPs), (ASP/VSPs), PSAPs as endpoints for emergency calls, mapping
services or other infrastructure elements that assist during the call
routing.

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|<--+---+
| | |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.

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o 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, or obtained via a third party method. Even if
location information is known to the network it might be made
available to the end host via DHCP (RFC 3825 [2]) or some other
mechanism. Alternatively, location information is used as part of
call routing and inserted by intermediaries.

o 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 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 VSP, ASP/VSP, e.g., either for enterprises or for
residential users.

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

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

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

(3) The emergency caller might need to consult a mapping service to
determine the PSAP 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) The emergency caller might get assistance for emergency call
routing by infrastructure elements that are Emergency Call Routing
Support entities, e.g., an Emergency Service Routing Proxy (ESRP), in
SIP).

(5) Location Information is used by emergency call routing entities
to determine the appropriate PSAP.
for subsequent mapping requests.

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

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(7) For infrastructure-based emergency call routing (in contrast to

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UE-based emergency call routing), the emergency call routing support
entity needs to forward the call to the PSAP.

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

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4. 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: provider existence: The initiation of
an IP-based emergency call SHOULD NOT assume the existence of an
Application/Voice Service Provider (ASP/VSP) SHOULD NOT be
assumed. (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 not be a telecommunication provider.

Re2. International: International applicability: Regional, political and
organizational aspects MUST be considered during the design of
protocols and protocol
extensions. 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 handle emergency calls.

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

Motivation: Once common standards are established, it The design mapping protocol must be 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, ASPs, ASP/VSPs,
IAPs or other participants.

Re4. Multiple modes: Multiple Multi-mode communication: IP-based emergency calls MUST support
multiple communication modes, such as including, for example, audio, video
and text MUST be supported (i.e., implemented in the
protocol, though not necessarily used in all calls). text.

Motivation: In PSTN, voice and text telephony (often called TTY or
textphone
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 [10]), instant
messaging and video.

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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. Differences of currency in mapping sources: For alternate
mapping, differences in currency between mapping data contained
within Currency indication: The mapping sources protocol SHOULD be minimized. support an
indicator describing how current the information provided by the
mapping source is.

Motivation: Alternative 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 ECRIT mapping protocol MUST return a URI (or URIs) 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, protocol needs to be usable within by any SIP capable phone
in
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. PSAP URI accessibility: The mapping information protocol MUST be available
without having support
interaction between the client and server where no enrollment to enroll with a
mapping service provider. 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 VSP. ASP/VSP.

Re9. No modification of location databases: Common data structures and formats: The mapping protocol SHOULD NOT require that
support common data within location structures and formats from the mapping
server.

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.

Motivation: Databases For example, a database which contain
contains civic addresses used within by location servers, servers may be used for
multiple purposes and applications beyond emergency service
location-to-PSAP URI mapping.

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5. Identifying

Re10. Anonymous mapping: The mapping protocol MUST NOT require the Caller's Location

Location can either be provided direct, or by reference, and
represents either a civic location, or as a geographic location. How
does
true identity of the target for which the location (or location reference) 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 [9]).

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5. Identifying the Caller's Location

Location can either be provided direct, or by reference, and
represents either a civic location, or as a geographic location. How
does the location (or location reference) become associated with the
call? 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 (RFC 3825 [2]) and
I-D.ietf-geopriv-dhcp-civil [7]) or utilizing the Link Layer
Discovery Protocol (LLDP) [see IEEE8021AB].

UA-referenced: The caller's user agent provides a pointer (i.e., a
location reference), via a permanent or temporary identifier, to
the location which is stored by a location service 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.

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

Lo2. Location provided: An Emergency Services Routing Proxy (ESRP) The mapping protocol MUST NOT remove retain any
location information which is provided to it, even after performing location
based routing. mapping
is performed.

Motivation: The ESRP and the PSAP use the same location
information object, but for a different purpose. Therefore, it is
imperative that the mapping protocol not remove location
Information so that the PSAP can still needs to receive the caller's caller
location.

Lo3. 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.

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6. Emergency Identifier

Id1. Universal emergency identifier setup: One or more universal
emergency identifiers

Lo4. Alternate community names: The mapping protocol MUST be recognized by any device or network
element for call setup purposes. support
both the jurisdictional community name and the postal community
name fields within the PIDF-LO data.

Motivation: There A mapping query must be some way for any device accepted with either or element to
recognize an emergency call throughout the call setup. This both
community name fields, and provide appropriate responses. If a
mapping query is
regardless of made with only one field present, and if the device location,
database contains both jurisdictional and postal, the application/voice service
provider used. An example mapping
protocol response should return both.

Lo5. Validation of this might be "urn:service:sos".

Id2. Emergency identifier resolution: Where multiple emergency
identifiers exist, there civic location: The mapping protocol MUST be a mechanism to differentiate each
emergency identifier used, support
civic address validation, based on the specific type of location, prior to initiating
an emergency
help requested. call.

Motivation: Some jurisdictions may have multiple types Location validation provides an opportunity to help
assure ahead of
emergency services available, (e.g., fire, police, ambulance), in
which case, it is important that any one could be selected
directly.

Id3. Emergency identifier marking: Any device in the signaling path
that recognizes by some means that time, whether or not successful mapping to the signaling
appropriate PSAP will likely occur when it is associated
with an required.
Validation may also help to avoid delays during emergency call
setup due to invalid locations.

Lo6. Validation resolution: The mapping protocol MUST add a specific emergency indication,
if it doesn't already exist, support the
ability to provide ancillary information about the signaling before forwarding
it. This marking mechanism must be different than QoS marking.

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.

Id4. Prevention resolution of fraud: A call MUST be routed
location data used to retrieve a PSAP if it is
identified as an emergency call. URI.

Motivation: This prevents The mapping server may not use of all the emergency call indication to
gain access data elements
in the provided location information to call features determine a match, or authentication override for non-
emergency purposes.

Id5. Extensibility of emergency identifiers: The list of defined
emergency identifiers MUST may
be extensible, and it is not necessary able to provide mapping find a match based on all of the information except for every possible service.

Motivation:
some specific data elements. The use uniqueness of an this information
set may be used to differentiate among emergency identifier is locally
determined.

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Id6. Discovery jurisdictions.
Precision or resolution in the context of emergency dial strings: 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: The mapping protocol MUST
support a mechanism to discover existing location-dependent emergency dial
strings, (e.g., "9-1-1", "1-1-2"), which are contextually
appropriate for the indicate and resolve any associated issues
attributed to a location or a part of the caller.

Motivation: Users are trained to dial the appropriate emergency
dial string to reach emergency services. There needs to be a way
to figure out what the dial string location that is within known to
not exist, despite the local environment receipt of the caller.

Id7. Local emergency dial string translation: An end device (i.e.,
SIP UA), SHOULD translate home emergency dial strings into
universal emergency identifiers. a successful mapping response.

Motivation: The UA would most likely be pre-
provisioned with the appropriate information in order emergency authority for a given jurisdiction may
provide a means to make such resolve addressing problems, e.g., a translation.

Id8. Emergency dial string replacement: For each signaling protocol URI for a
web service that can be used in to report problems with an emergency call, reserved universal
emergency identifiers SHOULD address.

Lo8. Limits to validation: Successful validation of a civic location
MUST NOT be allowed required to replace the original
emergency dial strings, based on local conventions, regulations,
or preference (e.g., as in the case of place an enterprise). emergency call.

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Motivation: Any signaling protocol requires the use of In some
identifier to indicate the called party, and the user terminal cases, a civic location may
lack not be considered
valid. This fact should not result in the capability call being dropped or
rejected by any entity along the call setup signaling path to determine the actual emergency address
(PSAP URI).
PSAP.

Lo9. 3D sensitive mapping: The use of local conventions mapping protocol MUST implement
support for both 2D and 3D location information, and may be required as accept
either a
transition mechanism. Note: Such use complicates international
movement of the user terminal, 2D or 3D mapping request as input.

Motivation: It is expected that provisioning systems will accept
both 2D and evolution to 3D data. When a standardized
universal emergency identifier or set of identifiers 3D request is preferred.

Id9. Universal emergency identifier recognition: A universal
emergency identifier MUST be recognized presented to an area
only defined by any network element
which supports 2D data, the mapping protocol.

Id10. Emergency identifier not recognized: A call MUST result would be recognized the same as an emergency call even
if the specific emergency service
requested is not recognized.

Motivation: In order to have a robust system that supports
incremental service deployment while still maintaining a fallback
capability.

Id11. Discovery of visited emergency dial strings: The mapping
protocol MUST support (i.e., implement, though not necessarily
use) a mechanism to allow height/altitude dimension was omitted in the end device to learn visited
emergency dial strings. request.

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

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7. Mapping Protocol

Given the requirement from the previous section, one of having a
universal emergency identifier that is independent of the caller's
location, and since each PSAP only serves 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 approaches to invoking a mapping service. 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 is outlined in the document
I-D.hardie-ecrit-lost [6].

For caller-based resolution, the caller's user agent invokes 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
(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. Appropriate PSAP: Calls MUST be routed to the PSAP responsible
for a 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: Routing to the wrong PSAP will result in delays in
handling emergencies as calls are redirected, and result in
inefficient use of PSAP resources at the initial point of contact.

Ma2. Minimal additional delay: The execution of the mapping protocol
SHOULD minimize the amount of additional delay to the overall
call-setup time.

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

Ma3. Referral:

6. Emergency Identifier

Id1. Emergency identifier support: The mapping protocol MUST support (i.e., Implement
for use), a mechanism
one or more emergency identifiers for the delivery back to mapping client
clients to be able to contact used for call setup purposes.

Motivation: Since there is a need for any mapping server and be referred device or network
element to another server that recognize an emergency call throughout the call setup,
there is more
qualified also a need to answer the query.

Motivation: This requirement alleviates have the potential for
incorrect configurations to cause calls to fail, particularly for
caller-based queries.

Ma4. Multiple response URIs: The mapping protocol response MUST provide support
for such an identifier. This is regardless of the inclusion device location
or the ASP/VSP used. An example of this kind of identifier might
be "urn:service:sos".

Id2. Emergency identifier resolution: Where multiple URIs in emergency
identifiers exist, the response.

Ma5. URI alternate contact: The mapping protocol MUST support be able to
differentiate between identifiers based on the
return specific type of a URI or contact method explicitly marked as an
alternate contact.
emergency help requested.

Motivation: In response to a mapping request, the mapping server Some jurisdictions may return an alternate URI. Implementation details to have multiple types of
emergency services available, (e.g., fire, police, ambulance), in
which case, it is important that any one could be
described within an operational document.

Ma6. URL properties: selected
directly.

Id3. Emergency identifier marking: The mapping protocol MUST support include
an emergency identifier with the ability
to provide additional information that allows signaling, if one does not exist,
for the mapping client
to determine relevant properties purpose of marking the URL. call as an emergency call.

Motivation: In some cases, the same geographic area is served Marking ensures proper handling as an emergency call
by
several PSAPs, downstream elements that may not recognize, for example, a corporate campus might be served by
both
local variant of a corporate security department and the municipal PSAP. The
mapping protocol should then return URLs for both, with
information allowing the querying entity to choose one or the
other. logical emergency address, etc. This determination could marking
mechanism is assumed to be made by either different than a QoS marking mechanism.

Id4. Prevention of fraud: If a call is identified as an ESRP, based
on local policy, or by direct user choice, in emergency
call, the case of caller-
based methods.

Ma7. Traceable resolution: The mapping protocol SHOULD MUST support the
ability that call being
successfully routed to a PSAP.

Motivation: This prevents use of the mapping client emergency call indication to be able
gain access to determine the entity call features or entities which provided the emergency address resolution
information.

Motivation: It is important authentication override for public safety reasons, that there non-
emergency purposes.

Id5. Extensible emergency identifiers: The mapping protocol MUST
support an extensible list of emergency identifiers, though it is a method
not required to provide operational traceability in case mapping for every possible service.

Motivation: The use of errors. an emergency identifier is locally
determined.

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Ma8. URI for error reporting:

Id6. Discovery of emergency dial string: The mapping protocol MUST
support
(i.e., implement for use) a mechanism to return a URI that can be
used discover an existing location-dependent
emergency dial string, (e.g., "9-1-1", "1-1-2"), which are
contextually appropriate for the location of the caller.

Motivation: Users are trained to report dial the appropriate emergency
dial string to reach emergency services. There needs to be a suspected or known error way
to figure out what the dial string is within the mapping
database.

Ma9. Resilience against failure: local environment
of the caller.

Id7. Home emergency dial string translation: The mapping protocol
MUST support
(i.e., implement for use) end device translation (e.g. SIP UA) of a mechanism to enable home
emergency dial string into an emergency identifier.

Motivation: The UA would most likely be pre-provisioned with the mapping client
appropriate information in order to make such a translation. The
mapping protocol would be able to fail over to another replica support either type for those
clients which may not support dial string translation.

Id8. Emergency dial string replacement: The mapping protocol SHOULD
support replacement of the mapping server,
so that original dial string with a failure reserved
emergency identifier for each signaling protocol used for an
emergency call. This replacement of a server does not endanger the ability to
perform the mapping.

Ma10. Incrementally deployable: The mapping protocol MUST original dial string
should be
designed based on local conventions, regulations, or preference
(e.g., as in such a way that supports the incremental deployment case of an enterprise).

Motivation: Any signaling protocol requires the use of some
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
mapping services.

Motivation: It must not local conventions may be necessary, for example, to have required as a
global street level database before deploying
transition mechanism. Note: Such use complicates international
movement of the system. It is
acceptable user terminal. Evolution to have some misrouting a standardized
emergency identifier or set of calls when the database does identifiers is preferred.

Id9. Emergency identifier not (yet) contain accurate PSAP service area information.

Ma11. Mapping requested from anywhere: recognized: The mapping protocol MUST
support (i.e., implement, though not necessarily use) the ability
to provide mapping information in response to queries from any
(earthly) location, regardless of where calls which are initiated as emergency calls even if the mapping client
specific emergency service requested 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 recognized, based on
the appropriate
PSAP, but must still be able emergency identifier used.

Motivation: In order to obtain have a mapping.

Ma12. Extensible protocol: robust system that supports
incremental service deployment while still maintaining a fallback
capability.

Id10. Discovery of visited emergency dial strings: 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, a mechanism to accommodate future
extensions allow the end device to location information learn
visited emergency dial strings.

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Motivation: Scenarios exist where a user dials a visited emergency
dial string that might be included in is different from the
PIDF-LO (RFC 4119 [3]).

Ma13. Split responsibility: The mapping protocol MUST support home emergency dial string:
If a user (i.e.,
implement for use) UA operator) visits a foreign country, observes a
fire truck with 999 on the division side, the expectation is one of data subset handling between
multiple mapping servers within being
able to dial that same number to summon a single level of fire truck. Another use
case cited is where a civic location
hierarchy.

Motivation: For example, two mapping servers for tourist collapses, and a "good Samaritan"
uses the same city or
county may handle different streets within tourist's cell phone to enter a home emergency dial
string appropriate for that city or county. foreign country.

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Ma14. Any time mapping: The

7. Mapping Protocol

There are two basic approaches to invoking a mapping service. 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 MUST support (i.e.,
implement for use) is outlined in the ability of document
I-D.hardie-ecrit-lost [6].

For caller-based resolution, the caller's user agent invokes a
mapping function service to be
invoked at any time, including while an determine the appropriate PSAP based on the
location provided. The resolution may take place well before the
actual emergency call is in
process and before an emergency placed, or at the time of the call.

Motivation: Used as

For mediated resolution, a fallback mechanism only, if call signaling server, such as a SIP
(outbound) proxy or redirect server invokes the mapping query
fails at emergency call time, it service.

Since servers may be advantageous used as outbound proxy servers by clients that
are not in the same geographic area as the proxy server, any proxy
server has to have prior
knowledge of the PSAP URI. This prior knowledge would be obtained
by performing a mapping query at able to translate any time prior caller location to an emergency
call.

Ma15. Baseline query protocol: A mandatory-to-implement protocol
MUST be specified.

Motivation: An over-abundance of similarly-capable choices appears
undesirable the
appropriate PSAP. (A traveler may, for interoperability.

Ma16. Multiple PSAP URIs: example, accidentally or
intentionally configure its home proxy server as its outbound proxy
server, even while far away from home.)

Ma1. Appropriate PSAP: The mapping protocol MUST support (i.e.,
implement, though not necessarily use), a method to be able the routing
of an emergency call to
return multiple URIs for different PSAPs that cover the same PSAP responsible for a particular
geographic area.

Ma17. Single URI per contact protocol: Though

Motivation: Routing to the mapping protocol
supports wrong PSAP will result in delays in
handling emergencies as calls are redirected, and result in
inefficient use of PSAP resources at the return initial point of multiple URIs, it SHOULD return only one
URI per contact protocol, so contact.
It is important that clients are the location determination mechanism not required be
fooled by the location of IP telephony gateways or dial-in lines
into a corporate LAN (and dispatch emergency help to
select among different targets for the same contact protocol.

Motivation: There may be two gateway
or more URIs returned when multiple
contact protocols are available (e.g., SIP campus, rather than the caller), multi-site LANs and SMS). The client
may select among multiple contact protocols based on its
capabilities, preference settings, or availability.

Ma18. Anonymous mapping: The mapping similar
arrangements.

Ma2. Minimal additional delay: Mapping protocol MUST NOT require execution SHOULD
minimize the
true identity amount of delay within the target for which the location information is
attributed. Ideally, no identity information is provided via the
mapping protocol. Where identity information is provided, it may overall call-setup time.

Motivation: Since outbound proxies will likely be in asked to resolve
the form of an unlinked pseudonym (RFC 3693 [9]).

Ma19. Location delivery by-value: same geographic coordinates repeatedly, a suitable time-
limited caching mechanism should be supported.

Ma3. Mapping referral: The mapping protocol MUST support
(i.e., implement, though not necessarily use) 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 mechanism
for the mapping protocol client to contact any mapping server and be
referred to another mapping server that is not required more qualified to support
answer the
ability to de-reference specific location references. query.

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Ma20. Alternate community names:

Motivation: To help avoid the case of relying on incorrect
configuration data which may cause calls to fail, particularly for
caller-based mapping queries.

Ma4. Multiple response URIs: The mapping protocol MUST support
both the jurisdictional community name and
possible inclusion of multiple URIs in a mapping response.

Motivation: Multiple URIs may be available from the postal community
name fields within mapping
server.

Ma5. URI alternate contact: In addition to returning a primary
contact, the PIDF-LO data.

Motivation: A mapping query must be accepted with either protocol MUST support the return of a URI or both
community name fields, and provide appropriate responses. If
contact method explicitly marked as an alternate contact.

Motivation: In response to a mapping query is made with only one field present, and if the
database contains both jurisdictional and postal, request, the mapping
protocol response should server
may return both.

Ma21. Ubiquitous triggering: an alternate URI. Implementation details to be
described within an operational document.

Ma6. URL properties: The mapping protocol MUST implement,
but not necessarily use, support the ability
to be invoked at any time,
from any location, by any client which supports provide ancillary information about a contact or URI that
allows the mapping
protocol. client to determine relevant properties of the
URL.

Motivation: While end devices are In some cases, the typical initiators of
mapping service requests, it same geographic area is also expected that other mapping
clients, such as relays, 3rd party devices, served by
several PSAPs, etc. may also
trigger for example, a mapping request.

Ma22. Validation of civic location: corporate campus might be served by
both a corporate security department and the municipal PSAP. The
mapping protocol MUST
implement a method via a mapping request, that makes it possible should then return URLs for a mapping server to validate a civic location prior both, with
information allowing the querying entity to that
location's use in an actual emergency call.

Motivation: Location validation provides choose one or the
other. This determination could be made by either an opportunity to help
assure ahead ESRP, based
on local policy, or by direct user choice, in the case of time, whether successful caller-
based methods.

Ma7. Traceable resolution: The mapping to protocol SHOULD support the
appropriate PSAP will likely occur when it is required.
Validation may also help
ability of the mapping client to avoid delays during be able to determine the entity
or entities which provided the emergency call
setup due address resolution
information.

Motivation: It is important for public safety reasons, that there
is a method to invalid locations.

Ma23. Validation resolution: provide operational traceability in case of errors.

Ma8. URI for error reporting: The mapping protocol MUST support
(i.e., required to implement, but not required for use) the
return of additional information which a URI that can be used to determine the
precision report a suspected or resolution of known
error within the data elements used to determine a
PSAP URI.

Motivation: The mapping server may not use all the data elements
in the provided location information database.

Motivation: If an error is returned, for example, there needs 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 URI which points to differentiate among emergency jurisdictions.
Precision a resource which can explain or resolution in the context of this requirement might
mean, for example, explicit identification of the data elements
that were used successfully in
potentially help resolve the mapping. error.

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Ma24. Indication

Ma9. Resilience against failure: The mapping protocol MUST support a
mechanism which enables fail over to different (replica) mapping
server in order to obtain a successful mapping.

Motivation: It is important that the failure of non-existent location: a single mapping
server does not preclude the mapping client's ability to receive
mapping from a different mapping server.

Ma10. Incrementally deployable: The mapping protocol MUST be
designed in such a way that supports the incremental deployment of
mapping services.

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.

Ma11. 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.

Motivation: Used as a fallback mechanism to indicate that a location or a part of a location is
known to not exist, even only, if a valid location-to-PSAP URI mapping
can query
fails at emergency call time, it may be provided. advantageous to have prior
knowledge of the PSAP URI. This includes prior knowledge would be obtained
by performing a way mapping query at any time prior to identify a separate
mechanism an emergency
call.

Ma12. Anywhere mapping: The mapping protocol MUST support the
ability to resolve provide mapping information in response to an
individual query from any such discrepancy. (earthly) location, regardless of where
the mapping client is located, either geographically or by network
location.

Motivation: The emergency authority for a given jurisdiction mapping client, such as an ESRP, may
provide a means to resolve addressing problems, e.g., a URI for a
web service that can not
necessarily be used anywhere close to report problems with an address.

Ma25. Limits the caller or the appropriate
PSAP, but must still be able to validation: Successful validation of a civic
location obtain mapping information.

Ma13. Extensible protocol: The mapping protocol MUST NOT be required designed to place an emergency call.
support the extensibility of location data elements, both for new
and existing fields.

Motivation: In some cases, a civic This is needed, for example, to accommodate future
extensions to location may not information that might be considered
valid. This fact should not result included in the call being dropped or
rejected by any entity along the signaling path to the PSAP.

Ma26. 3D sensitive mapping:
PIDF-LO (RFC 4119 [3]).

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Ma14. Split responsibility: The mapping protocol MUST implement support for both 2D and 3D the
division of data subset handling between multiple mapping servers
within a single level of a civic location information, and hierarchy.

Motivation: For example, two mapping servers for the same city or
county may accept
either a 2D handle different streets within that city or 3D mapping request as input. county.

Ma15. Baseline query protocol: A mandatory-to-implement protocol
MUST be specified.

Motivation: It is expected that provisioning systems will accept
both 2D and 3D data. When An over-abundance of similarly-capable choices appears
undesirable for interoperability.

Ma16. Multiple PSAP URIs: The mapping protocol MUST support a 3D request is presented method
to an area
only defined by 2D data, receive multiple PSAP URIs which cover the same geographic
area.

Motivation: Two different mapping result would be servers may cover the same as
if
geographic area, and therefore have the height/altitude dimension was omitted in same set of coverage
information.

Ma17. Single URI per contact protocol: Though the request. mapping protocol
supports the return of multiple URIs, it SHOULD return only one
URI per contact protocol, 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.

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8. Security Considerations

Security considerations are discussed in the ECRIT security document
I-D.taylor-ecrit-security-threats
I-D.ietf-ecrit-security-threats [4] .

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9. Contributors

The information contained in this document is a result of a joint
effort based on individual contributions by those involved in the
ECRIT WG. The contributors 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

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10. Acknowledgments

In addition to thanking those listed above, we would like to also
thank Guy Caron, Barry Dingle, Keith Drage, Tim Dunn, Patrik
Faeltstroem, 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, Hannes Tschofenig, and Nate Wilcox, for their
invaluable input.

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11. References

11.1. Normative References

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

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

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

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

[5] Schulzrinne, H., "A Uniform Resource Name (URN) for Services",
draft-ietf-ecrit-service-urn-00
draft-ietf-ecrit-service-urn-02 (work in progress),
February April 2006.

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

[7] 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.

11.2. Informative References

[8] 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.

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

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

[11] Wijk, A., "Framework of requirements for real-time text
conversation over IP using SIP", draft-ietf-sipping-toip-03
draft-ietf-sipping-toip-04 (work in progress), September 2005. March 2006.

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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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