ECRIT H. Schulzrinne
Internet-Draft Columbia U.
Expires: November 18, 2006 R. Marshall, Ed.
TCS
May 17, 2006
Requirements for Emergency Context Resolution with Internet
Technologies
draft-ietf-ecrit-requirements-09.txt
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Copyright (C) The Internet Society (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 . . . . . . . . . . . . . . 15
6. Emergency Service Identifier . . . . . . . . . . . . . . . . . 18
7. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 25
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 27
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
12.1. Normative References . . . . . . . . . . . . . . . . . . 29
12.2. Informative References . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30
Intellectual Property and Copyright Statements . . . . . . . . . . 31
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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 [2]) 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.
Outlined within this document are 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 service 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).
The primary intent of the mapping protocol is to produce a PSAP URI
(from a preferred set of URIs, e.g., SIP:URI, SIPS:URI) based on both
location information [6] and a service identifier in order to
facilitate the IP end-to-end completion of an emergency call. Aside
from obtaining a PSAP URI, the mapping protocol is useful for
obtaining other information as well. There may be a case, for
example, where an appropriate dial string is not known, only
location. The mapping protocol can then return a geographically
appropriate dial string based on the input.
Since some PSAPs may not immediately support IP, or because some end
devices (UAs) may not initially support emergency service URNs, it
may be necessary to also support emergency service identifiers that
utilize less preferred URI schemes, such as a tel URI in order to
complete an emergency call via the PSTN.
Identification of the caller, while not incompatible with the
requirements for messaging outlined within this document, is
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considered to be outside the scope of this document.
Location is required for two separate purposes, first, to support the
routing of the emergency call to the appropriate PSAP and second, to
display the caller's location to the call taker for help in
dispatching emergency assistance to the appropriate 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],
with the qualification that unless otherwise stated these words apply
to the design of the mapping protocol, not its implementation or
application.
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.
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.)
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.
Application Service Provider (ASP): The organization or entity that
provides application-layer services, which may include voice (see
"Voice Service Provider"). This entity can be a private
individual, an enterprise, a government, or a service provider.
An ASP is more general than a Voice Service Provider, since
emergency calls may use other media beyond voice, including text
and video. For a particular user, the ASP may or may not be the
same organization as his IAP or ISP.
Voice Service Provider (VSP): A specific type of Application Service
Provider which provides voice related services based on IP, such
as call routing, a SIP URI, or PSTN termination. In this
document, unless noted otherwise, any reference to "Voice Service
Provider" or "VSP" may be used interchangeably with "Application/
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Voice Service Provider" or "ASP/VSP".
Emergency Service Routing Proxy (ESRP): An ESRP is an emergency call
routing support entity that invokes the location-to-PSAP URI
mapping, to return either the URI for the appropriate PSAP, or the
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)).
Emergency Call Routing Support (ECRS): An intermediary function which
assists in the routing of an emergency call via IP. An ESRP is an
example of an Emergency call routing support entity.
Public Safety Answering Point (PSAP): Physical location where
emergency calls are received under the responsibility of a public
authority. (This terminology is used by both ETSI, in ETSI SR 002
180, and NENA.) In the United Kingdom, PSAPs are called Operator
Assistance Centres, in New Zealand, Communications Centres.
Within this document, it is assumed, unless stated otherwise, that
PSAP is that which supports 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.
Location: A geographic identification assigned to a region or feature
based on a specific coordinate system, or by other precise
information such as a street number and name. It can be either a
civic or geographic location.
Civic location: A described location based on some defined grid, such
as a jurisdictional, postal, metropolitan, or rural reference
system, (e.g., street address).
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.
Location validation: A caller location is considered valid if the
civic or geographic location is recognizable within an acceptable
location reference system (e.g., USPS, WGS-84, etc.), 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.
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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
an emergency service identifier, since each represents specific
emergency dial string key sequences which are recognized within a
local geographic area or jurisdiction.
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.
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.
Service identifier: A general identifier that has applicability to
both emergency and non-emergency contexts (specifically referred
to within this document as "emergency service identifier").
Service URN: An implementation of a service identifier, which has
applicability to both emergency and non-emergency contexts (e.g.,
urn:service:sos, urn:service:info, etc.) Within this document,
service URN is specifically referred to as 'emergency service URN'
[8].
Emergency service identifier (ESI): A specific service identifier
that is used to request a PSAP URI in order to initiate an
emergency call, and may be used to mark any call as an emergency
call. An ESI is a more general term than 'emergency service URN',
since it could also refer to an alternate identifier, such as a
tel URI (Section 6).
Emergency service URN: An emergency-context specific service URN that
is an implementation of an emergency service identifier (e.g.,
urn:service:sos). Is often referred to as, and is equivalent with
'sos service URN'.
PSAP URI: The URI (e.g., SIP:URI, SIPS:URI, XMPP:URI, etc.) at which
the PSAP may be contacted with an emergency call. This contact
could be done directly, or via an intermediary, (e.g., ESRP).
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Mapping: The process of resolving a location to one or more PSAP URIs
which directly identify a PSAP, or point to an intermediary which
knows about a PSAP and that is designated as responsible to serve
that location.
Mapping client: A mapping client interacts with the mapping server to
learn one or more PSAP URIs for a given location.
Mapping protocol: A protocol used to convey the mapping request and
response.
Mapping server: The mapping server holds information about the
location-to-PSAP URI mapping.
Mapping service: A network service which uses a distributed mapping
protocol, to perform a mapping between a location and a PSAP, or
intermediary which knows about the PSAP, and is used to assist in
routing an emergency call.
(Emergency) caller: The term "caller" or "emergency caller" refer to
the person placing an emergency call or sending an emergency
instant message (IM).
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.
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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 (ASP/VSPs), Emergency Call Routing Support (ECRS)
providers, mapping service providers, and PSAPs.
This section outlines which entities will be considered in the
routing scenarios discussed.
Location
Information +-----------------+
|(1) |Internet | +-----------+
v |Attachment | | |
+-----------+ |Provider | | Mapping |
| | | (3) | | Service |
| Emergency |<---+-----------------+-->| |
| Caller | | (2) | +-----------+
| |<---+-------+ | ^
+-----------+ | +----|---------+------+ |
^ | | Location | | |
| | | Information<-+ | |
| +--+--------------+ |(5) | | (6)
| | | | |
| | +-----------v+ | |
| (4) | |Emergency | | |
+--------------+--->|Call Routing|<--+---+
| | |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, made available via DHCP (RFC 3825 [4]) or some
other mechanisms. 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 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 (or other relevant information) that is
appropriate for the physical location of the emergency caller,
possibly considering other attributes such as appropriate language
support by the emergency call taker.
(4) 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
for subsequent mapping requests.
(6) Emergency call routing support entities might need to consult a
mapping service to determine where to route the emergency call.
(7) For infrastructure-based emergency call routing (in contrast to
UE-based emergency call routing), the emergency call routing support
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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 existence: The initiation of
an IP-based emergency call SHOULD NOT assume the existence of an
Application/Voice Service Provider (ASP/VSP).
Motivation: The caller may not have an application/voice service
provider. For example, a residence may have its own DNS domain
and run its own SIP proxy server for that domain. On a larger
scale, a university might provide voice services to its students
and staff, but might not be a telecommunication provider.
Re2. International applicability: Regional, political and
organizational aspects MUST be considered during the design of
protocols and protocol extensions which support IP-based emergency
calls.
Motivation: It must be possible for a device or software developed
or purchased in one country to place emergency calls in another
country. System components should not be biased towards a
particular set of emergency numbers or languages. Also, different
countries have evolved different ways of organizing emergency
services, e.g., either centralizing them or having smaller
regional subdivisions such as United States counties or
municipalities handle emergency calls.
Re3. Distributed administration: Deployment of IP-based emergency
services MUST NOT depend on a sole central administration
authority.
Motivation: The design mapping protocol must make it possible to
deploy and administer emergency calling features on a regional or
national basis without requiring coordination with other regions
or nations. The system cannot assume, for example, that there is
a single global entity issuing certificates for PSAPs, ASP/VSPs,
IAPs or other participants.
Re4. Multi-mode communication: IP-based emergency calls MUST support
multiple communication modes, including, for example, audio, video
and text.
Motivation: In PSTN, voice and text telephony (often called TTY or
text-phone in North America) are the only commonly supported
media. Emergency calling must support a variety of media. Such
media should include voice, conversational text (RFC 4103 [5]),
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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. Currency indication: The mapping protocol SHOULD support an
indicator describing how current the information provided by the
mapping source is.
Motivation: This is especially useful when an alternate mapping is
requested, and alternative sources of mapping data may not have
been created or updated with the same set of information or within
the same timeframe. Differences in currency between mapping data
contained within mapping sources should be minimized.
Re7. Mapping result usability: The mapping protocol MUST return one
or more URIs that are usable within a standard signaling protocol
(i.e., without special emergency extensions).
Motivation: For example, a SIP specific URI which is returned by
the mapping protocol needs to be usable by any SIP capable phone
within a SIP initiated emergency call. This is in contrast to a
"special purpose" URI, which may not be recognizable by a legacy
SIP device.
Re8. PSAP URI accessibility: The mapping protocol MUST support
interaction between the client and server where no enrollment to a
mapping service exists or is required.
Motivation: The mapping server may well be operated by a service
provider, but access to the server offering the mapping must not
require use of a specific ISP or ASP/VSP.
Re9. Common data structures and formats: The mapping protocol SHOULD
support common data 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. For example, a database which
contains civic addresses used by location servers may be used for
multiple purposes and applications beyond emergency service
location-to-PSAP URI mapping.
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Re10. Anonymous mapping: The mapping protocol MUST NOT require the
true identity of the target for which the location information is
attributed.
Motivation: Ideally, no identity information is provided via the
mapping protocol. Where identity information is provided, it may
be in the form of an unlinked pseudonym (RFC 3693 [3]).
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5. Identifying the Caller's Location
Location can either be provided directly, or by reference, and
represents either a civic location, or a geospatial location. An
important question is how and when to attach location information to
the VoIP emergency signaling. In general, we can distinguish three
modes of operation of how a location is associated with an emergency
call:
UA-inserted: The caller's user agent inserts the location information
into the call signaling message. The location information is
derived from sources such as GPS, DHCP (see [4] for geospatial
location information and [10]) for civic location information 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 server somewhere else
and then retrieved by the PSAP, ESRP, or other authorized service
entity.
Proxy-inserted: A proxy along the call path inserts the location or
location reference.
Lo1. Reference datum: The mapping protocol MUST support the WGS-84
coordinate reference system and MAY support other coordinate
reference systems.
Lo2. Location object/info preservation: The mapping protocol MUST
retain any location information which is provided to it, even
after mapping is performed.
Motivation: The ESRP and the PSAP use the same location
information object, but for a different purpose. Therefore, it is
imperative that the mapping protocol does not remove the location
information from the messaging, so that it can be provided to the
PSAP.
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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Lo4. Alternate community names: The mapping protocol MUST support
both the jurisdictional 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, and if the
database contains both jurisdictional and postal, the mapping
protocol response should return both.
Lo5. Validation of civic location: The mapping protocol MUST support
location validation for civic location (street addresses).
Motivation: Location validation provides an opportunity to help
assure ahead of time, whether or not a successful mapping to the
appropriate PSAP will likely occur when it is required.
Validation may also help to avoid delays during emergency call
setup due to invalid locations.
Lo6. Validation resolution: The mapping protocol MUST support the
ability to provide ancillary information about the resolution of
location data used to retrieve a PSAP URI.
Motivation: The mapping server may not use all the data elements
in the provided location information to determine a match, or may
be able to find a match based on all of the information except for
some specific data elements. The uniqueness of this information
set may be used to differentiate among emergency jurisdictions.
Precision or resolution in the context of this requirement might
mean, for example, explicit identification of the data elements
that were used successfully in the mapping.
Lo7. Indication of non-existent location: The mapping protocol MUST
support a mechanism to indicate and resolve any associated issues
attributed to a location or a part of a location that is known to
not exist, despite the receipt of a successful mapping response.
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.
Lo8. Limits to validation: Successful validation of a civic location
MUST NOT be required to place an emergency call.
Motivation: In some cases, a civic location may not be considered
valid. This fact should not result in the call being dropped or
rejected by any entity along the call setup signaling path to the
PSAP.
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Lo9. 3D sensitive mapping: The mapping protocol MUST implement
support for both 2D and 3D location information, and may accept
either a 2D or 3D mapping request as input.
Motivation: It is expected that end devices or location servers
will provide either 2D or 3D data. When a 3D request is presented
within an area only defined by 2D data within the mapping server,
the mapping result would be the same as if the height/altitude
dimension was omitted in the request.
Lo10. Database type indicator: The mapping protocol MAY support a
mechanism which provides an indication describing a specific
"type" of location database used.
Motivation: It is useful to know the source of the data stored in
the database used for location validation. This is applicable for
either civic or geographic location matching (e.g., USPS, MSAG,
GDT, etc.).
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6. Emergency Service Identifier
The term, service identifier, is a general term that incorporates all
service URNs [8], but which may also refer to other identifiers which
are not service URNs, for example, a tel URI. In protocol exchanges,
any request to invoke an emergency service along with the specific
type of emergency service desired, such as fire department or police,
is indicated by the service URN.
Since this document addresses only emergency service context specific
requirements for mapping, the terms service identifier and service
URN, which have a more general applicability than that of only
emergency services, are replaced by the terms "emergency service
identifier" and "emergency service URN", respectively, throughout
this document. The term "sos service URN" is used interchangeably
with "emergency service URN".
Id1. Emergency service identifier support: The mapping protocol MUST
be able to return one or multiple emergency service identifiers in
response to a query.
Motivation: Since there is a need for any device or network
element to recognize an emergency call throughout the call setup,
there is also a need to have the mapping protocol provide support
for such an identifier. This is regardless of the device location
or the ASP/VSP used. An example of this kind of identifier might
be the emergency service URN, 'urn:service:sos'.
Id2. Emergency service identifier resolution: Where multiple
emergency service identifiers exist, the mapping protocol MUST be
able to differentiate between ESIs based on the specific type of
emergency help requested.
Motivation: Some jurisdictions may have multiple types of
emergency services available, (e.g., fire, police, ambulance), in
which case, it is important that any one could be selected
directly.
Id3. Extensible emergency service identifiers: The mapping protocol
MUST support an extensible list of emergency identifiers, though
it is not required to provide mapping for every possible service.
Motivation: The use of an emergency service identifier is locally
determined.
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Id4. Discovery of emergency dial string: There MUST be support for a
mechanism to discover an existing location-dependent emergency
dial string, (e.g., "9-1-1", "1-1-2"), contextually 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.
Id5. Home emergency dial string translation: There MUST be support
for end device translation (e.g. SIP UA) of a home emergency dial
string into an emergency service identifier.
Motivation: The UA would most likely be pre-provisioned with the
appropriate information in order to make such a translation. The
mapping protocol would be able to support either type for those
clients which may not support dial string translation.
Id6. Emergency dial string replacement: There SHOULD be support for
replacement of the original dial string with a reserved emergency
service identifier for each signaling protocol used for an
emergency call. This replacement of the original dial string
should be 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. Evolution to a standardized
emergency service identifier or set of identifiers is preferred.
Id7. Emergency service identifier marking: There MUST be support for
an emergency service identifier to be used for marking the call as
an emergency call.
Motivation: Marking ensures proper handling as an emergency call
by downstream elements that may not recognize, for example, a
local variant of a logical emergency address, etc. This marking
mechanism is assumed to be different than a QoS marking mechanism.
Id8. Emergency service identifier not recognized: There MUST be
support for calls which are initiated as emergency calls even if
the specific emergency service requested is not recognized, based
on the emergency service identifier used.
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Motivation: In order to have a robust system that supports
incremental service deployment while still maintaining a fallback
capability.
Id9. Discovery of visited emergency dial strings: There MUST be
support for a mechanism to allow the end device to learn visited
emergency dial strings.
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 home emergency dial
string appropriate for that foreign country.
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7. Mapping Protocol
There are two basic approaches to invoke the mapping protocol. We
refer to these as caller-based and mediated. In each case, the
mapping client initiates a request to a mapping server via a mapping
protocol. A proposed mapping protocol is outlined in the document
I-D.hardie-ecrit-lost [9].
For caller-based resolution, the caller's user agent invokes the
mapping protocol to determine the appropriate PSAP based on the
location provided. The resolution may take place well before the
actual emergency call is placed, or at the time of the call.
For mediated resolution, an emergency call routing support entity,
such as a SIP (outbound) proxy or redirect server invokes the mapping
service.
Since servers may be used as outbound proxy servers by clients that
are not in the same geographic area as the proxy server, any proxy
server has to be able to translate any caller location to the
appropriate PSAP. (A traveler may, for example, accidentally or
intentionally configure its home proxy server as its outbound proxy
server, even while far away from home.)
Ma1. Baseline query protocol: A mandatory-to-implement protocol MUST
be specified.
Motivation: An over-abundance of similarly-capable choices appears
undesirable for interoperability.
Ma2. Extensible protocol: The mapping protocol MUST be designed to
support the extensibility of location data elements, both for new
and existing fields.
Motivation: This is needed, for example, to accommodate future
extensions to location information that might be included in the
PIDF-LO (RFC 4119 [6]).
Ma3. 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.
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Ma4. Any time mapping: The mapping protocol MUST support the ability
of the mapping function to be invoked at any time, including while
an emergency call is in process and before an emergency call.
Motivation: Used as a fallback mechanism only, if a mapping query
fails at emergency call time, it may be advantageous to have prior
knowledge of the PSAP URI. This prior knowledge would be obtained
by performing a mapping query at any time prior to an emergency
call.
Ma5. Anywhere mapping: The mapping protocol MUST support the ability
to provide mapping information in response to an individual query
from any (earthly) location, regardless of where the mapping
client is located, either geographically or by network location.
Motivation: The mapping client, such as an ESRP, may not
necessarily be anywhere close to the caller or the appropriate
PSAP, but must still be able to obtain mapping information.
Ma6. Appropriate PSAP: The mapping protocol MUST support the routing
of an emergency call to the PSAP responsible for a particular
geographic area.
Motivation: Routing to the wrong PSAP will result in delays in
handling emergencies as calls are redirected, and result in
inefficient use of PSAP resources at the initial point of contact.
It is important that the location determination mechanism not be
fooled by the location of IP telephony gateways or dial-in lines
into a corporate LAN (and dispatch emergency help to the gateway
or campus, rather than the caller), multi-site LANs and similar
arrangements.
Ma7. Multiple PSAP URIs: The mapping protocol MUST support a method
to return multiple PSAP URIs which cover the same geographic area.
Motivation: Two different mapping servers may cover the same
geographic area, and therefore have the same set of coverage
information.
Ma8. Single primary URI per contact protocol: Though the mapping
protocol supports multiple URIs being returned, it SHOULD return
only one primary URI per contact protocol used, so that clients
are not required to select among different targets for the same
contact protocol.
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Motivation: There may be two or more URIs returned when multiple
contact protocols are available (e.g., SIP and SMS). The client
may select among multiple contact protocols based on its
capabilities, preference settings, or availability.
Ma9. URI alternate contact: In addition to returning a primary
contact, the mapping protocol MUST support the return of a PSAP
URI or contact method explicitly marked as an alternate contact
for use when a fallback contact is needed.
Motivation: In response to a mapping request, the mapping server
will also return an alternate URI. Implementation details to be
described within an operational document.
Ma10. Non-preferred URI schemes: The mapping protocol MAY support
the return of a less preferred URI scheme, (e.g., TEL URI).
Motivation: In order to provide incremental support to non-IP
PSAPs it may be necessary to be able to complete an emergency call
via the PSTN.
Ma11. URI properties: The mapping protocol MUST support the ability
to provide ancillary information about a contact that allows the
mapping client to determine relevant properties of the PSAP URI.
Motivation: In some cases, the same geographic area is served by
several PSAPs, for example, a corporate campus might be served by
both a corporate security department and the municipal PSAP. The
mapping protocol should then return URIs for both, with
information allowing the querying entity to choose one or the
other. This determination could be made by either an ESRP, based
on local policy, or by direct user choice, in the case of caller-
based methods.
Ma12. Mapping referral: The mapping protocol MUST support a
mechanism for the mapping client to contact any mapping server and
be referred to another mapping server that is more qualified to
answer the query.
Motivation: To help avoid the case of relying on incorrect
configuration data which may cause calls to fail, particularly for
caller-based mapping queries.
Ma13. Split responsibility: The mapping protocol MUST support the
division of data subset handling between multiple mapping servers
within a single level of a civic location hierarchy.
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Motivation: For example, two mapping servers for the same city or
county may handle different streets within that city or county.
Ma14. URL for error reporting: The mapping protocol MUST support the
ability to return a URL that can be used to report a suspected or
known error within the mapping database.
Motivation: If an error is returned, for example, there needs to
be a URL which points to a resource which can explain or
potentially help resolve the error.
Ma15. Resiliance to failure: The mapping protocol MUST support a
mechanism which enables fail over to different (replica) mapping
server in order to obtain and return a successful mapping to the
mapping client.
Motivation: It is important that the failure of a single mapping
server does not preclude the mapping client's ability to receive
mapping from a different mapping server.
Ma16. Traceable resolution: The mapping protocol SHOULD support the
ability of the mapping client to be able to determine the entity
or entities that provided the emergency address resolution
information.
Motivation: It is important for public safety reasons, that there
is a method to provide operational traceability in case of errors.
Ma17. Minimal additional delay: Mapping protocol execution SHOULD
minimize the amount of delay within the overall call-setup time.
Motivation: Since outbound proxies will likely be asked to resolve
the same geographic coordinates repeatedly, a suitable time-
limited caching mechanism should be supported.
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8. Security Considerations
Threats and security requirements are discussed in a separate
document, see I-D.ietf-ecrit-security-threats [7] .
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9. IANA Considerations
This document does not require actions by the IANA.
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10. Contributors
The information contained in this document is a result of a several
original joint contributions of text, which was then discussed and
refined by those and many others within the working group. These
contributors to the early text include, Nadine Abbott, Hideki Arai,
Martin Dawson, Motoharu Kawanishi, Brian Rosen, Richard Stastny,
Martin Thomson, James Winterbottom.
The contributors can be reached at:
Nadine Abbott nabbott@telcordia.com
Hideki Arai arai859@oki.com
Martin Dawson Martin.Dawson@andrew.com
Motoharu Kawanishi kawanishi381@oki.com
Brian Rosen br@brianrosen.net
Richard Stastny Richard.Stastny@oefeg.at
Martin Thomson Martin.Thomson@andrew.com
James Winterbottom James.Winterbottom@andrew.com
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11. 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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12. References
12.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
12.2. Informative References
[2] Charlton, N., Gasson, M., Gybels, G., Spanner, M., and A. van
Wijk, "User Requirements for the Session Initiation Protocol
(SIP) in Support of Deaf, Hard of Hearing and Speech-impaired
Individuals", RFC 3351, August 2002.
[3] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004.
[4] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location
Configuration Information", RFC 3825, July 2004.
[5] Hellstrom, G. and P. Jones, "RTP Payload for Text
Conversation", RFC 4103, June 2005.
[6] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[7] Taylor, T., "Security Threats and Requirements for Emergency
Call Marking and Mapping", draft-ietf-ecrit-security-threats-01
(work in progress), April 2006.
[8] Schulzrinne, H., "A Uniform Resource Name (URN) for Services",
draft-ietf-ecrit-service-urn-02 (work in progress), April 2006.
[9] Hardie, T., "LoST: A Location-to-Service Translation Protocol",
draft-hardie-ecrit-lost-00 (work in progress), March 2006.
[10] 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] Wijk, A., "Framework for real-time text over IP using SIP",
draft-ietf-sipping-toip-04 (work in progress), 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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