ECRIT H. Schulzrinne
Internet-Draft Columbia U.
Expires: August 31, 2006 R. Marshall, Ed.
TCS
February 27, 2006
Requirements for Emergency Context Resolution with Internet
Technologies
draft-ietf-ecrit-requirements-05.txt
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Copyright (C) The Internet Society (2006).
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 . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. High-Level Requirements . . . . . . . . . . . . . . . . . . . 12
5. Identifying the Caller Location . . . . . . . . . . . . . . . 14
6. Emergency Identifier . . . . . . . . . . . . . . . . . . . . . 16
7. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . 25
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 26
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
11.1. Normative References . . . . . . . . . . . . . . . . . . 28
11.2. Informative References . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
Intellectual Property and Copyright Statements . . . . . . . . . . 30
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1. Introduction
Users of both voice-centric (telephone-like) and non voice type
services (e.g. text messaging for hearing disabled users, (RFC 3351
[7]) 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, (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
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).
Identification of the caller, while not incompatible with the
requirements for messaging outlined within this document, is not
currently considered within the scope of the ECRIT charter, and is
therefore, left for a future draft to describe.
Note: Location is required for two separate purposes, first, to route
the call to the appropriate PSAP and second, to display the caller's
location to the call taker for help in dispatching emergency
assistance to the correct location.
Ideally, the mapping protocol would yield a URI from a preferred set
of URIs (e.g. sips:uri; sip:uri), which would allow an emergency call
to be completed using IP end-to-end (possibly via the Internet).
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, such as a TEL URI which may be used to complete a call over the
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PSTN.
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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.
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 defined as something more general than a Voice Service
Provider, since emergency calls are sometimes likely to use other
media, including text and video. Note: For a particular user, the
ASP may or may not be the same organization as the IAP and/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 scheme (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 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 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,
useful for call routing and completion of the emergency call.
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 Service 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 the WGS-84 datum)
Home emergency dial-string: A home emergency dial-string (ref.
Location-dependent emergency identifier) represents a sequence of
digits that is used to initiate an emergency call within a
geographic vicinity considered to be a user's "home" location or
vicinity.
Internet Attachment Provider (IAP): An organization that provides
physical network connectivity to its customers or users, e.g.
through digital subscriber lines, cable TV plants, Ethernet,
leased lines or radio frequencies. 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.
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. 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 prime meridian.
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Location Context Mapping System (LCMS): A system defined as a set of
mechanisms and services working together to perform a mapping,
(or, direct association), between a location and a PSAP uri
designated as responsibleto to serve that location.
Location-dependent emergency identifier: Location-dependent emergency
identifiers, also referred to as "emergency dial-strings" within
this document, 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 emergency identifier, since each represents specific
emergency identifiers 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 (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 of resolving a location 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 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.
Mapping service: A network service which uses a distributed mapping
protocol to provide information about the 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
IP. It is also assumed that the PSAP is reachable by IP-based
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protocols, such as SIP for call signaling and RTP for media.
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 identifier: An emergency identifier which is recognized by
any compatible endpoint, from any geographic location as useful
for initiating an emergency request. A general approach to using
universal identifiers is outlined in the service URN draft
(I-D.schulzrinne-sipping-service [5]).
Visited emergency dial-string: A visited emergency dial-string (ref.
Location-dependent emergency identifier) represents a sequence of
digits that is used to initiate an emergency call within a
geographic vicinity other than a user'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.
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3. Basic Actors
In order to support emergency services covering a large physical area
various infrastructure elements are necessary: Internet Attachment
Providers, Application/Voice Service Providers, PSAPs as endpoints
for emergency calls, mapping 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) |Internet | +-----------+
v |Attachment | | |
+-----------+ |Provider | | Mapping |
| | | (3) | | Service |
| 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 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.
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 Internet Attachment 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
Internet Attachment Provider (e.g., using DHCP or application layer
signaling protocols).
o (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 (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 mapping service 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.
o (8) Location Information is used by emergency call routing entities
to determine appropriate PSAP mapping.
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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 Service Provider: The existence of an Application
Service Provider (ASP) SHOULD NOT be assumed.
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: Regional, political and organizational aspects
MUST be considered during the design of protocols and protocol
extensions.
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 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, IAPs or other participants.
Re4. Multiple Modes: Multiple communication modes, such as audio,
video and text messaging MUST be supported (i.e. implemented in
the protocol, though not necessarily used).
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 [9]), instant
messaging and video.
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Re5. Alternate Mapping Sources: The mapping protocol SHOULD
implement a mechanism that allows for the retrieval of mapping
information, possibly of different degrees of currency.
Motivation: This provides the possibility of having available
alternative sources of mapping information when the normal source
is unavailable or unreachable, without specifying the means by
which the alternative source is created or updated.
Re6. Incremental Deployment: The ECRIT mapping protocol MUST return
URIs that are usable 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.
Re7. Ubiquitous Triggering: The mapping protocol MUST implement,
(not necessarily use), the ability to be invoked at any time, from
any location, by any client which supports the mapping protocol.
Motivation: While end devices are the typical initiators of
mapping service requests, it is also expected that other mapping
clients, such as relays, 3rd party devices, PSAPs, etc. may also
trigger a mapping request.
Re8. 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.
Re9. No Modification of Location Databases: The mapping protocol
SHOULD NOT require that data within location databases be
transformed or modified in any unusual or unreasonable way in
order for the mapping protocol to use the data.
Motivation: Databases which contain civic addresses (used within
location information servers), may be used for multiple purposes
and applications, (in addition to being used for emergency service
mapping only).
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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 (RFC 3825 [2])
and I-D.ietf-geopriv-dhcp-civil [6]) or utilizing the Link Layer
Discovery Protocol (LLDP) [see IEEE8021AB].
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.
Lo1. Validation of Civic Location: The mapping protocol MUST
implement a method that makes it possible for a mappng server to
validate a civic location prior to that location's use in an
actual emergency call.
Motivation: Location validation provides an opportunity to help
assure ahead of time, whether successful mapping to the
appropriate PSAP will likely occur when it is required.
Validation may also help to avoid delays during emergency call
setup due to invalid locations.
Lo2. Validation Resolution: The mapping protocol MUST support (i.e.
required to implement, though not required for use) the return of
additional information which can be used to determine the
precision or resolution of the data elements used to determine a
PSAP URI, for example.
Motivation: The mapping server may not use all the data elements
in the provided location information to determine a match, or may
be able to find a match based on all of the information except for
some specific data elements. The uniqueness of this information
set may be used to differentiate among emergency jurisdictions.
Precision or resolution in the context of this requirement might
mean, for example, explicit identification of the data elements
that were used successfully in the mapping.
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Lo3. Indication of non-existent location: The protocol MUST support
(i.e. must implement in the protocol, though not necessarily use)
a mechanism to indicate that a location or a part of a location is
known to not exist, even if a valid location-to-PSAP uri mapping
can be provided. This mechanism includes a means to identify a
separate mechanism that could be used to resolve the discrepancy.
Motivation: The emergency authority for a given jurisdiction may
provide a means to resolve addressing problems, e.g., a URI for a
web service that can be used to report problems with an address.
The mapping response would allow this service to be identified.
Lo4. Limits to Validation: Successful validation of a civic location
MUST NOT be required to enable any feature that is part of the
emergency call process.
Motivation: In some cases, (based on a variety of factors), a
civic location may not be considered valid. This fact should not
result in the call being dropped or rejected by any entity along
the signaling path to the PSAP.
Lo5. Reference Datum: The mapping server MUST implement support for
the WGS-84 coordinate reference system and may implement support
for use of other reference systems.
Lo6. 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.
Lo7. 3D Sensitive Mapping: The mapping protocol MUST implement
support for both 2D and 3D location information, and may accept
either a 2D or 3D mapping request as input, so to return an
appropriate result, based on which type of input is used.
Motivation: It is expected that provisioning systems will accept
both 2D and 3D data. When a 3D request is presented to an area
only defined by 2D data, the mapping result would be the same as
if the height/altitude dimension was omitted on the request."
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6. Emergency Identifier
Id1. 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.*.
Id2. Universal Identifier Resolution: Where multiple emergency
service types exist, the mapping protocol MUST support (i.e.
implement, though not necessarily use) the individual treatment of
each emergency identifier used, based on the specific type of
emergency help requested.
Motivation: Some jurisdictions may have multiple types of
emergency services available at the same level, (e.g. fire,
police, ambulance), in which case it is important that any one
could be selected directly.
Id3. Emergency Marking: Any device in the signaling path that
recognizes by some means that the signaling is associated with an
emergency call MUST add a specific emergency indication, if it
doesn't already exist, to 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. Emergency Identifier-based Marking: User agents, proxies, and
other network elements that process signaling associated with
emergency calls SHOULD be configured to recognize a reasonable
selection of logical emergency identifiers as a means to initiate
emergency marking.
Motivation: Since user devices roam, emergency identifiers may
vary from region to region. It is therefore important that a
network entity be able to perform mapping and/or call routing
within the context of its own point of origin rather than relying
on non-local logical emergency identifiers as the only basis for
emergency marking of calls.
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Id5. Prevention of Fraud: A call MUST be routed to a PSAP if it is
identified as an emergency call or is marked as such in accordance
with the above emergency marking requirements.
Motivation: this prevents use of the emergency call indication to
gain access to call features or authentication override for non-
emergency purposes.
Id6. Extensibility of emergency service types: The list of emergency
service types MUST be extensible, and it is not necessary to
provide mapping for every possible service type.
Motivation: The use of a service type is locally determined.
Id7. Discovery of emergency dial-string: The mapping protocol MUST
support (i.e. implement, though not necessarily use) a mechanism
to discover existing location-dependent emergency identifiers,
known as emergency dial-strings, (e.g. 9-1-1, 1-1-2), appropriate
for the location 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 is within the local environment
of the caller.
Id8. Local Identifier Translation: The SIP UA SHOULD translate home
emergency dial-strings to universal emergency identifiers. The UA
would most likely be pre-provisioned with the appropriate
information in order to make such a translation. This assumes
that a mechanism to provide the user's home emergency dial-strings
be available.
Id9. Emergency Identifier Replacement: For each signaling protocol
that can be used in an emergency call, reserved identifiers SHOULD
be allowed to replace the original emergency identifier, based on
local conventions, regulations, or preference (e.g. as in the case
of an enterprise).
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 local conventions may be required as a
transition mechanism. Note: Such use complicates international
movement of the user terminal, and evolution to a standardized
universal emergency identifier or set of identifiers is preferred.
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Id10. Universal Identifier Recognition: Universal identifier(s),
MUST be universally recognizable (as the label suggests), by any
network element which supports the (ECRIT) mapping protocol.
Id11. Universal Identifier Unrecognized: A call MUST be recognized
as 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."
Id12. Translation of emergency dial-strings: The SIP UA SHOULD
translate both home and visited emergency dial-strings into a
universal emergency identifier.
Id13. Detection of visited emergency dial-strings: The mapping
protocol MUST support (i.e. implement, though not necessarily
use), a mechanism to allow the end device to learn visited
emergency dial-strings.
Motivation: Scenarios exist where a user dials a visited emergency
dial-string that is different from the home emergency dial-string:
If a user of a UA visits a foreign country, observes a fire truck
with 999 on the side, the expectation is to be 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 dial a local emergency number.
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7. Mapping Protocol
Given the requirement from the previous section, that of a single (or
small number of) emergency identifier(s) which are independent of the
caller's location, and since PSAPs only serve a limited geographic
region, and for reasons of jurisdictional and local knowledge, having
the call reach the appropriate PSAP based on a mapping protocol, is
crucial.
There are two basic architectures described for translating an
emergency identifier into the appropriate PSAP emergency address. We
refer to these as caller-based and mediated.
For caller-based resolution, the caller's user agent consults a
mapping service to determine the appropriate PSAP based on the
location provided. The resolution may take place well before the
actual emergency call is placed, or at the time of the call.
For mediated resolution, a call signaling server, such as a SIP
(outbound) proxy or redirect server performs this function (a request
for mapping) by invoking the mapping protocol.
Note that this case relies on an architecture where the call is
effectively routed to a copy of the database, rather than having some
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 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, there may be a finer resolution of
routing (which the caller isn't aware of), which results in a
particular "accredited" PSAP (i.e. one run by local authorities)
answering to call. (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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Ma1. Appropriate PSAP: Calls MUST be routed to the PSAP responsible
for this particular geographic area. In particular, the location
determination should not be fooled by the location of IP telephony
gateways or dial-in lines into a corporate LAN (and dispatch
emergency help to the gateway or campus, rather than the caller),
multi-site LANs and similar arrangements.
Motivation: 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. Mapping redirection: The mapping protocol MUST support (i.e.
implement for use) redirection functionality, since in some cases,
an initial mapping may provide a single URL for a large geographic
area. Redirection is needed to then re-invokes the mapping
protocol on a different database to obtain another URL for a more
resolute ESRP or PSAP, which covers a smaller area.
Motivation: The more local the mapping output is, the more
favorable (in most cases) the likely outcome will be for the
emergency caller.
Ma3. 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.
Ma4. Referral: The mapping protocol MUST support (i.e. Implement
for use), a mechanism for the mapping client to be able to contact
any mapping 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.
Ma5. Multiple Response URIs: The mapping protocol response MUST
support (i.e. implement, though not necessarily use), the
inclusion of multiple URIs in the response.
Motivation: In response to a mapping request, a server will
normally provide a URI or set of URIs for contacting the
appropriate PSAP.
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Ma6. URI - Alternate Contact: The mapping protocol MUST support
(i.e. implement, though not necessarily use), the return of a URI
or contact method explicitly marked as an alternate contact.
Motivation: In response to a mapping request, if an expected URI
is unable to be returned, then mapping server may return an
alternate URI. When and how this would be used will be described
in an operational document.
Ma7. Multiple PSAP URIs: The mapping protocol MUST support (i.e.
implement, though not necessarily use), a method to be able to
return multiple URIs for different PSAPs that cover the same area.
Ma8. URL properties: The mapping protocol MUST support (i.e.
implement, though not necessarily use), the ability to 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.
Ma9. Traceable resolution: The mapping protocol SHOULD support the
ability of the mapping client to be able to determine the entity
or entities which provided the emergency address resolution
information.
Motivation: To provide operational traceability in case of errors.
Ma10. URI for error reporting: The mapping protocol MUST support
(i.e. implement for use) a mechanism to return a URI that can be
used to report a suspected or known error within the mapping
database.
Ma11. Resilience against server failure: The mapping protocol MUST
support (i.e. implement for use) a mechanism to enable the mapping
client to 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.
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Ma12. 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 boundary information.
Ma13. Mapping requested from anywhere: 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 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.
Ma14. Location Updates: The mapping protocol MUST support (i.e.
implement, though not necessarily use) the ability to provide
location updates. Mapping services should implement the
mechanisms to provide updated location.
Motivation: Updated location information may have an impact on
PSAP routing. In some cases it may be possible to redirect that
call to a more appropriate PSAP (some device measurement
techniques provide quick (i.e. early), but imprecise "first fix"
location).
Ma15. Extensible Protocol: The mapping protocol MUST be designed to
support the extensibility of location data elements, both for new
and existing fields.
Motivation: This is needed, for example, to accommodate future
extensions to location information that might be included in the
PIDF-LO (RFC 4119 [3]).
Ma16. Split responsibility: The mapping protocol MUST support (i.e.
implement for use) the division of data subset handling between
multiple mapping servers within a single level of a civic location
hierarchy.
Motivation: For example, two directories for the same city or
county may handle different streets within that city or county.
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Ma17. Pervasive Mapping: The mapping protocol MUST support (i.e.
implement for use) the ability of the mapping function to be
invoked at any time, including while an emergency call is in
process.
Ma18. Baseline query protocol: A mandatory-to-implement protocol
MUST be specified.
Motivation: An over-abundance of similarly-capable choices appears
undesirable for interoperability.
Ma19. Single URI Scheme: The mapping protocol MAY return multiple
URIs, though it SHOULD return only one URI per scheme, 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.
Ma20. Separation of Identity from mapping: The mapping protocol MUST
NOT require the true identity of 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 be in the form of an unlinked pseudonym as
defined in RFC 3963.
Ma21. Location delivery by-value: The mapping protocol MUST support
(i.e. implement, though not necessarily use) the delivery of
location information by-value, though may alternatively support
de-referencing of specific location references.
Motivation: Location by-reference is not one of the evaluation
criteria for a mapping protocol presented here. (i.e. the mapping
protocol is not required to support the ability to de-reference
specific location references.)
Ma22. Alternate community names: The mapping protocol MUST support
(i.e. implement, though not necessarily use) both the jurisdiction
community name and the postal community name fields within the
PIDF-LO data.
Motivation: A mapping query must be accepted with either or both
community name fields, and provide appropriate responses. If a
mapping query is made with only one field present, given that the
database has both fields populated, the mapping protocol response
should return both available fields.
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Ma23. Support for alias locations: The mapping protocol MUST support
(i.e. implement, though not necessarily use) one or more aliases
for a specific location entry.
Motivation: It should be possible to relate one entry to another
and be able to determine which is the "primary" entry and which is
the alias. The result of aliasing is always that mapping from the
primary or any of the aliases is the same.
Ma24. Pre-call mapping for fallback: The mapping protocol MUST
support (i.e. implement, though not necessarily use) LCMS queries
prior to making an emergency call.
Motivation: Used as a fallback mechanism only, if a LCMS query
fails at emergency call time, it may be advantageous to have prior
knowledge of the PSAP URI. This prior knowledge would be obtained
by performing an LCMS query at any time prior to an emergency
call.
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8. Security Considerations
Note: Security Considerations are referenced in the ECRIT security
document [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 Michael Hammer, Ted Hardie, Marc Linsner, Barbara Stark, Clive
D.W. Feather, Keith Drage, Raymond Forbes, Tim Dunn, Steve Norreys,
Patti McCalmont, Rohan Mahy, Nate Wilcox, Michael Haberler, Jonathan
Rosenberg, Shida Schubert, John Schnizlein, Benny Rodrig, John
Rosenberg, Patrik Faeltstroem, Barry Dingle, Gunnar Hellstrom, James
Seng, Byron Smith, Cullen Jennings, Don Mitchell, John Morris, Jon
Peterson, Randall Gellens, Guy Caron, Andrew Newton, James Polk, Tom
Taylor, and Hannes Tschofenig 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., "Security Threats and Requirements for
Emergency Calling", draft-taylor-ecrit-security-threats-01 (work
in progress), December 2005.
[5] Schulzrinne, H., "A Uniform Resource Name (URN) for Services",
draft-schulzrinne-sipping-service-01 (work in progress),
October 2005.
[6] 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
[7] 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.
[8] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004.
[9] Hellstrom, G. and P. Jones, "RTP Payload for Text
Conversation", RFC 4103, June 2005.
[10] Wijk, A., "Framework of requirements for real-time text
conversation using SIP", draft-ietf-sipping-toip-03 (work in
progress), September 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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