ecrit H. Schulzrinne
Internet-Draft Columbia U.
Expires: March 6, 2006 R. Marshall, Ed.
TCS
September 2, 2005
Requirements for Emergency Context Resolution with Internet Technologies
draft-ietf-ecrit-requirements-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document enumerates requirements for 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. High-Level Requirements . . . . . . . . . . . . . . . . . . . 10
5. Identifying the Caller Location . . . . . . . . . . . . . . . 12
6. Emergency Identifier . . . . . . . . . . . . . . . . . . . . . 13
7. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 15
8. Emergency Caller Identification . . . . . . . . . . . . . . . 19
9. Performance and Reliability Considerations . . . . . . . . . . 20
10. Security Considerations . . . . . . . . . . . . . . . . . . . 21
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 22
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
13.1. Normative References . . . . . . . . . . . . . . . . . . 24
13.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
Intellectual Property and Copyright Statements . . . . . . . . . . 26
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1. Introduction
Users of voice-centric, (telephone-like) IP-based services expect to
be able to call for emergency help, such as police, the fire
department, or ambulance services, regardless of where they are, what
(if any) service provider they are using, or what type of device they
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
in the public circuit-switched telephone network (PSTN) are not quite
appropriate for evolving IP-based voice, text and real-time
multimedia communications. This document outlines the key
requirements that 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 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, (Internet
device), and terminates to an IP-capable PSAP, done entirely over an
IP network.
This document outlines the various functional issues which relate to
making an IP-based emergency call, including a description of general
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), the mapping function
required to route the call to the appropriate PSAP, (Section 7), and
finally, identifying who placed the call, (Section 8)
Note that 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.
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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] and
indicate requirement levels for compliant implementations.
Since a requirements document does not directly specify a protocol to
implement, these compliance labels should be read as indicating
requirements for the protocol or architecture, rather than an
implementation.
For lack of a better term, we will use the term "caller" or
"emergency caller" to refer to the person placing an emergency call
or sending an emergency IM.
Access Infrastructure Provider (AIP): 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.
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
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).
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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 sip:uri, sips:uri, or tel:uri which represents
the network address of the PSAP useful for the completion of a
VoIP emergency call.
emergency caller: The user or user device entity which sends his/her
location to another entity in the network.
emergency identifier: The numerical and/or text identifier which is
supplied by a user or a user device, which identifies the call as
an emergency call and is translated into an emergency address for
call routing and completion.
enhanced emergency service: Enhanced emergency services add the
ability to identify the caller identity and/or caller location to
basic emergency services. (Sometimes, only the caller location
may be known, e.g. from a public access point that is not owned by
an individual.)
ESRP (Emergency Services Routing Proxy): An ESRP is a call routing
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
system, the ESRP would typically be a SIP proxy, but could also be
a Back-to-back user agent (B2BUA).
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 WGS-84 datum)
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.
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 address. In the geocoding process,
the location is defined with an x,y coordinate value according to
the distance north or south of the equator and east or west of the
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prime meridian.
location validation: A caller location is considered valid if the
civic or geographic location is recognizable within an acceptable
location reference systems (e.g. USPS, WGS84, etc.), and can be
mapped to one or more PSAPs. Location validation ensures that a
location is reference able, but makes no 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 Client: A Mapping Client interacts with the Mapping Server to
learn one or multiple URIs for a given address.
Mapping Server: The Mapping Server holds information about the
address to URI mappings.
Miniumum Connectivity: A minimum set of [physical, virtual...??]
connectivity between two endpoints.
[Ed. Send additional text.]
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
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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3. Basic Actors
In order to support emergency services covering a large physical area
various infrastructure elements are necessary: Access Infrastructure
Providers, Application (Voice) Service Provider, PSAPs as endpoints
for emergency calls, directory services or other infrastructure
elements that assist in during the call routing and potentially many
other entities.
This section outlines which entities will be considered in the
routing scenarios discussed.
Location
Information +-----------------+
|(1) |Access | +-----------+
v |Infrastructure | | |
+-----------+ |Provider | | Directory |
| | | (3) | | |
| Emergency |<---+-----------------+-->| |
| Caller | | (2) | +-----------+
| |<---+-------+ | ^
+-----------+ | +----|---------+------+ |
^ | | Location | | |
| | | Information<-+ | |
| +--+--------------+ |(8) | | (5)
| | +-----------v+ | |
| (4) | |Emergency | | |
+--------------+--->|Call Routing|<--+---+
| | |Support | |
| | +------------+ |
| | ^ |
| | (6) | +----+--+
| (7) | +------->| |
+--------------+--------------->| PSAP |
| | |
|Application +----+--+
|(Voice) |
|Service |
|Provider |
+---------------------+
Figure 1: Framework
Figure 1 shows the interaction between the entities involved in the
call. There are a number of different deployment choices, as it can
be easily seen from the figure. The following deployment choices
need to be highlighted:
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o How is location information provided to the end host? It might
either be known to the end host itself (due to manual configuration
or provided via GPS) or available via a third party. Even if
location information is known to the network it might be made
available to the end host. Alternatively, location information is
used as part of call routing and inserted by intermediaries.
o Is the Access Infrastructure 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.
Please note that the overlapping squares aim to indicate that certain
functionality can be collapsed into a single entity. As an example,
the Application (Voice) Service Provider might be the same entity as
the Access Infrastructure Provider and they might also operate the
PSAP. There is, however, no requirement that this must be the case.
Additionally it is worth pointing out that end systems might be its
own VSP, e.g., for enterprises or residential users.
Below, we describe various interactions between the entities shown in
Figure 1 are described:
o (1) Location information might be available to the end host itself.
o (2) Location information might, however, also be obtained from the
Access Infrastructure Provider (e.g., using DHCP or application layer
signaling protocols).
o (3) The Emergency Caller might need to consult a directory to
determine the PSAP that is appropriate for the physical location of
the emergency caller (and considering other attributes such as a
certain language support by the Emergency Call Takers).
o (4) The Emergency Caller might get assistance for emergency call
routing by infrastructure elements (referred as Emergency Call
Routing Support entities). In case of SIP these entities are
proxies.
o (5) Individual Emergency Call Routing Support entities might need
to consult a directory to determine where to route the emergency
call.
o (6) The Emergency Call Routing Support entities need to finally
forward the call, if infrastructure based emergency call routing is
used.
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o (7) The emergency caller might interact directly with the PSAP
without any 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.
R1. Application Service Provider: The existence of an Application
Service Provider (ASP) MUST NOT be assumed.
Motivation: The caller may not have a 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.
R2. International: The protocols and protocol extensions developed
MUST support regional, political and organizational differences.
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.
R3. Distributed Administration: Deployment of emergency services
MUST NOT depend on a sole central administration authority.
Motivation: Once common standards are established, it must be
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, AIPs or other participants.
R4. Multiple Modes: Multiple communication modes, such as audio,
video and text messaging MUST be supported.
Motivation: In PSTN, voice and text telephony (often called TTY or
textphone 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 [6]),
instant messaging and video.
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R5. Minimum Connectivity: An emergency call SHOULD succeed as long
as there is a working network path between the caller and the
PSAP. In particular, reliance during call set-up and calls on
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
terms section (per ietf63 ecrit meeting minutes note), but still
no resolution for the above.]
R6. Incremental Deployment: The ECRIT mapping protocol MUST return
URIs that are useable by a standard signaling protocol (i.e.,
without special emergency extensions) unless an error is returned.
Motivation: The format of the output returned by the mapping
protocol is in a standard format for communication protocol. For
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
context. Special purpose URIs would not be understood by "legacy"
SIP devices since they do not have knowledge about the mapping
protocol, and therefore are not to be used.
R7. Relay Services: It SHOULD be possible to involve relay services
in the call for translation between different modes.
Motivation: It should be possible to connect the relay service so
that the direct flow of media to the emergency service is
maintained. In addition, it should be possible to convey
telemetry data, such as data from automobile crash sensors.
D1. PSAP Identification: The mapping information MUST be available
without having to enroll with a service provider.
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.
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5. Identifying the Caller Location
Location can either be provided directly, 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, derived from sources such as GPS, DHCP or link-layer
announcements (LLDP).
UA-referenced: The caller's user agent provides a 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.
Proxy-inserted: A proxy along the call path inserts the location or
location reference.
L6. Validation of civic location: It MUST be possible to validate an
address prior to its use in an actual emergency call.
Motivation: Location validation refers to a process to determine
whether or not a given civic location is valid or not.
L10. Preferred datum: The preferred coordinate reference system for
emergency calls MUST be WGS-84.
L28. Location Provided: An Emergency Services Routing Proxy (ESRP)
MUST NOT remove location information after performing location
based routing.
Motivation: The ESRP and the PSAP use the same location
information object but for a different purpose. Therefore, the
PSAP still requires the receipt of information which represents
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.
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6. Emergency Identifier
A1a. Universal Identifier - Setup: One or more universal emergency
identifiers MUST be recognized by any device or network element
for call setup purposes
Motivation: There must be some way for any device or element to
recognize an emergency call throughout the call setup. This is
regardless of the device location, the application (voice) service
provider used (if any at all), or of any other factor. Examples
of these might include: 911, 112, and sos.*.
A1b. Universal Identifier - Mapping: One or more universal emergency
identifiers MUST be recognized by any device or network element to
support mapping.
Motivation: Mapping must be made to work under all circumstances,
by any network element or device. This is regardless of the
device location, the application (voice) service provider used (if
any at all), or of any other factor. Examples of these might
include: 911, 112, and sos.*.
A1c. Emergency Marking: Emergency requests which are not already
marked as emergency calls, MUST be recognizable and marked by user
agents, proxies, and other network elements as emergency calls.
Motivation: SIP and other call signaling protocols are not
specific to one country or service provider and devices are likely
to be used across national or service provider boundaries. Since
services such as disabling mandatory authentication for emergency
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
agents, proxies and other network elements.
Motivation: To prevent fraud, an address identified as an
emergency number for call features or authentication override MUST
also cause routing to a PSAP.
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A4. Minimal configuration: Any local emergency identifiers SHOULD be
configured automatically, without user intervention.
Motivation: A new UA "unofficially imported" into an organization
from elsewhere should have the same emergency capabilities as one
officially installed.
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7. Mapping Protocol
There are two approaches for triggering the mapping protocol: caller-
based, or mediated.
From the previous section, we take the requirement of a single (or a
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
emergency identifier into the appropriate PSAP emergency address. We
refer to these as caller-based and mediated. In caller-based
resolution, the caller's user agent consults a directory and
determines the appropriate PSAP based on its location.
For mediated resolution, a call signaling server, such as a SIP
(outbound) proxy or redirect server performs this function. Note
that the latter case includes the architecture where the call is
effectively routed to a copy of the database, rather than having some
non-SIP protocol query the database. 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.)
The resolution may take place well before the actual emergency call
is placed, or at the time of the call.
The problem at hand is more difficult to resolve than that for
traditional web or email services. In this case, the emergency
caller only dialed an emergency identifier, and depending on the
location, any one of several thousand PSAPs around the world could be
appropriate PSAP. In addition, the caller probably does not care
which specific PSAP answers the call, but rather that it be an
accredited PSAP, e.g. one run by the local government authorities.
(Many PSAPs are run by private entities. For example, universities
and corporations with large campuses often have their own emergency
response centers.)
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I1. Appropriate PSAP: Calls MUST be routed to the PSAP responsible
for this particular geographic area.
Motivation: 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.
I3. Mapping redirection: The mapping protocol MUST support
redirection functionality.
Motivation: In some cases, an initial mapping may provide a single
URL for a large geographic area. The ESRP identified by that URL
then re-invokes the mapping protocol on a different database to
obtain another URL for an ESRP or PSAP covering a smaller area.
D5. Minimal additional delay: The execution of the mapping protocol
SHOULD minimize the amount of additional delay to the overall
call-setup time.
Motivation: Since outbound proxies will likely be asked to resolve
the same geographic coordinates repeatedly, a suitable time-
limited caching mechanism should be supported.
D7. Referral: The mapping client MUST be able to contact any server
and be referred to another server that is more qualified to answer
the query.
Motivation: This requirement alleviates the potential for
incorrect configurations to cause calls to fail, particularly for
caller-based queries.
I4. Return multiple PSAPs: The mapping protocol MUST be able to
return multiple URLs for different PSAPs that cover the same area.
The mapping protocol must provide additional information that
allows the querying entity to determine relevant properties of the
URL.
Motivation: In some cases, the same geographic area is served by
several PSAPs, for example, a corporate campus might be served by
both a corporate security department and the municipal PSAP. The
mapping protocol should then return URLs for both, with
information allowing the querying entity to choose one or the
other. This determination could be made by either an ESRP, based
on local policy, or by direct user choice, in the case of caller-
based trigger methods.
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I7. Traceable resolution: The entity requesting mapping SHOULD be
able to determine the entity or entities who provided the
emergency address resolution information.
I8. 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.
I10. Incrementally deployable: The mapping function MUST be capable
of being deployed incrementally.
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 boundary information.
I13. Verify mapping support: The mapping protocol SHOULD support the
ability for a requesting entity to verify that mapping services
are available for a referenced location.
Motivation: It should be possible to make sure ahead of time, that
requests for emergency services will work when needed.
I25. Mapping requested from anywhere: The mapping protocol MUST be
able to provide the mapping regardless of where the mapping client
is located, either geographically or by network location.
Motivation: The mapping client, (such as the ESRP), may not
necessarily be anywhere close to the caller or the appropriate
PSAP, but must still be able to obtain a mapping.
I31: 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.
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.
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I39. Location Updates: It SHOULD be possible to have updates of
location.
Motivation: Updated location information may change call routing,
(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
inclusion of new location fields.
Motivation: This is needed, for example, to accommodate future
extensions to location information that might be included in the
PIDF-LO (I-D.ietf-geopriv-pidf-lo-03 [2])
I41. Split responsibility: The mapping protocol MUST allow that
within a single level of the civic address hierarchy, multiple
mapping servers handle subsets of the data elements.
Motivation: For example, two directories for the same city or
county may handle different streets within that city or county.
I42. The mapping function MUST be able to be invoked at any time,
including while an emergency call is in process.
D9. Baseline query protocol: A mandatory-to-implement protocol MUST
be specified.
Motivation: An over-abundance of similarly-capable choices appears
undesirable for interoperability.
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8. Emergency Caller Identification
TEXT REQUESTED
[Ed. This section was never here, but was requested (H.
Schulzrinne, 8/09/05 email.).]
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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.]
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10. Security Considerations
Note: Security Considerations are referenced in the ECRIT security
document [3].
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11. 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 mdawson@nortelnetworks.com
Motoharu Kawanishi kawanishi381@oki.com
Brian Rosen br@brianrosen.net
Richard Stastny Richard.Stastny@oefeg.at
Martin Thomson marthom@nortelnetworks.com
James Winterbottom winterb@nortelnetworks.com
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12. Acknowledgments
We would like to thank James Polk, Ted Hardie and Andrew Newton for
their input.
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13. References
13.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Peterson, J., "A Presence-based GEOPRIV Location Object Format",
draft-ietf-geopriv-pidf-lo-03 (work in progress),
September 2004.
[3] Tschofenig, H., "Security Threats and Requirements for Emergency
Calling", draft-tschofenig-ecrit-security-threats-01 (work in
progress), July 2005.
13.2. Informative References
[4] 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.
[5] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004.
[6] Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation",
RFC 4103, June 2005.
[7] Wijk, A., "Framework of requirements for real-time text
conversation using SIP", draft-ietf-sipping-toip-02 (work in
progress), August 2005.
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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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