< draft-ietf-ecrit-requirements-10.txt   draft-ietf-ecrit-requirements-11.txt >
ECRIT H. Schulzrinne ECRIT H. Schulzrinne
Internet-Draft Columbia U. Internet-Draft Columbia U.
Expires: December 11, 2006 R. Marshall, Ed. Expires: December 3, 2006 R. Marshall, Ed.
TCS TCS
June 9, 2006 June 2006
Requirements for Emergency Context Resolution with Internet Requirements for Emergency Context Resolution with Internet
Technologies Technologies
draft-ietf-ecrit-requirements-10.txt draft-ietf-ecrit-requirements-11
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Abstract Abstract
This document enumerates requirements for the context resolution of This document defines terminology and enumerates requirements for the
emergency calls placed by the public using voice-over-IP (VoIP) and context resolution of emergency calls placed by the public using
general Internet multimedia systems, where Internet protocols are voice-over-IP (VoIP) and general Internet multimedia systems, where
used end-to-end. Internet protocols are used end-to-end.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Requirements Terminology . . . . . . . . . . . . . . . . . . 5
3. Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . . 9 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 6
4. High-Level Requirements . . . . . . . . . . . . . . . . . . . 12 3.1 Emergency Services . . . . . . . . . . . . . . . . . . . . 6
5. Identifying the Caller's Location . . . . . . . . . . . . . . 15 3.2 Service Providers . . . . . . . . . . . . . . . . . . . . 6
6. Emergency Service Identifier . . . . . . . . . . . . . . . . . 18 3.3 Actors . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 21 3.4 Call Routing Entities . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 25 3.5 Location . . . . . . . . . . . . . . . . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 3.6 Identifiers, Numbers and Dial Strings . . . . . . . . . . 8
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.7 Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 9
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28 4. Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . 11
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5. High-Level Requirements . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . 29 6. Identifying the Caller's Location . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 29 7. Emergency Service Identifier . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30 8. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . 22
Intellectual Property and Copyright Statements . . . . . . . . . . 31 9. Security Considerations . . . . . . . . . . . . . . . . . . 27
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 28
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 29
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 30
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
13.1 Normative References . . . . . . . . . . . . . . . . . . 31
13.2 Informative References . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 32
Intellectual Property and Copyright Statements . . . . . . . 33
1. Introduction 1. Introduction
Users of both voice-centric (telephone-like) and non voice type Users of both voice-centric (telephone-like) and non-voice services
services (e.g., text communication for hearing disabled users (RFC such as text communication for hearing disabled users (RFC 3351 [3])
3351 [2]) have an expectation to be able to initiate a request for expect to be able to initiate a request for help in case of an
help in case of an emergency. emergency.
Unfortunately, the existing mechanisms to support emergency calls Unfortunately, the existing mechanisms to support emergency calls
that have evolved within the public circuit-switched telephone that have evolved within the public circuit-switched telephone
network (PSTN) are not appropriate to handle evolving IP-based voice, network (PSTN) are not appropriate to handle evolving IP-based voice,
text and real-time multimedia communications. This document outlines text and real-time multimedia communications. This document outlines
the key requirements that IP-based end systems and network elements, the key requirements that IP-based end systems and network elements,
such as SIP proxies, need to satisfy in order to provide emergency such as Session Initiation Protocol (SIP) [2] proxies, need to
call services, which at a minimum, offer the same functionality as satisfy in order to provide emergency call services, which at a
existing PSTN services, with the additional overall goal of making minimum, offer the same functionality as existing PSTN services, with
emergency calling more robust, less costly to implement, and the additional overall goal of making emergency calling more robust,
multimedia-capable. less costly to implement, and multimedia-capable.
This document only focuses on end-to-end IP-based calls, i.e., where This document only focuses on end-to-end IP-based calls, i.e., where
the emergency call originates from an IP end system and terminates the emergency call originates from an IP end system and terminates in
into an IP-capable PSAP, conveyed entirely over an IP network. an IP-capable PSAP, conveyed entirely over an IP network.
Outlined within this document are various functional issues which We first define terminology in Section 3. The document then outlines
relate to placing an IP-based emergency call, including a description various functional issues which relate to placing an IP-based
of baseline requirements (Section 4), identification of the emergency emergency call, including a description of baseline requirements
caller's location (Section 5), use of an service identifier to (Section 5), identification of the emergency caller's location
declare a call to be an emergency call (Section 6), and finally, the (Section 6), use of a service identifier to declare a call to be an
mapping function required to route the call to the appropriate PSAP emergency call (Section 7), and finally, the mapping function
(Section 7). required to route the call to the appropriate PSAP (Section 8).
The primary intent of the mapping protocol is to produce a PSAP URI The primary purpose 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 drawn from a preferred set of URI schemes such as SIP or SIPS URIs,
location information [6] and a service identifier in order to based on both location information [9] and a service identifier in
facilitate the IP end-to-end completion of an emergency call. Aside order to facilitate the IP end-to-end completion of an emergency
from obtaining a PSAP URI, the mapping protocol is useful for call.
Aside from obtaining a PSAP URI, the mapping protocol is useful for
obtaining other information as well. There may be a case, for obtaining other information as well. There may be a case, for
example, where an appropriate dial string is not known, only example, where an appropriate emergency number is not known, only
location. The mapping protocol can then return a geographically location. The mapping protocol can then return a geographically
appropriate dial string based on the input. appropriate emergency number based on the input.
Since some PSAPs may not immediately support IP, or because some end Since some PSAPs may not immediately support IP, or because some user
devices (UAs) may not initially support emergency service URNs, it equipment (UE) may not initially support emergency service
may be necessary to also support emergency service identifiers that identifiers, it may be necessary to also support emergency service
utilize less preferred URI schemes, such as a tel URI in order to identifiers that utilize less preferred URI schemes, such as a tel
complete an emergency call via the PSTN. URI in order to complete an emergency call via the PSTN.
Identification of the caller, while not incompatible with the Identification of the caller, while not incompatible with the
requirements for messaging outlined within this document, is requirements for messaging outlined within this document, is
considered to be outside the scope of this document. considered to be outside the scope of this document.
Location is required for two separate purposes, first, to support the Location is required for two separate purposes, first, to support the
routing of the emergency call to the appropriate PSAP and second, to routing of the emergency call to the appropriate PSAP and second, to
display the caller's location to the call taker for help in display the caller's location to the call taker to help in
dispatching emergency assistance to the appropriate location. dispatching emergency assistance to the appropriate location.
2. Terminology 2. Requirements Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [1], and "OPTIONAL" are to be interpreted as described in RFC 2119 [1],
with the qualification that unless otherwise stated these words apply with the qualification that unless otherwise stated these words apply
to the design of the mapping protocol, not its implementation or to the design of the mapping protocol, not its implementation or
application. application.
Basic emergency service: Basic Emergency Service allows a user to 3. Terminology
3.1 Emergency Services
Basic emergency service: Basic emergency service allows a caller to
reach a PSAP serving its current location, but the PSAP may not be reach a PSAP serving its current location, but the PSAP may not be
able to determine the identity or geographic location of the able to determine the identity or geographic location of the
caller, except by having the call taker ask the caller. caller, except by the call taker asking the caller.
Enhanced emergency service: Enhanced emergency services add the Enhanced emergency service: In enhanced emergency service, the PSAP
ability to identify the caller's identity or location to basic call taker can determine the caller's current location.
emergency services. (Sometimes, only the caller location may be
known, e.g., when a call is placed from a public access point that 3.2 Service Providers
is not owned by an individual.)
Internet Attachment Provider (IAP): An organization that provides Internet Attachment Provider (IAP): An organization that provides
physical and layer 2 network connectivity to its customers or physical and data link (layer 2) network connectivity to its
users, e.g., through digital subscriber lines, cable TV plants, customers or users, e.g., through digital subscriber lines, cable
Ethernet, leased lines or radio frequencies. Examples of such TV plants, Ethernet, leased lines or radio frequencies. Examples
organizations include telecommunication carriers, municipal of such organizations include telecommunication carriers,
utilities, larger enterprises with their own network municipal utilities, larger enterprises with their own network
infrastructure, and government organizations such as the military. infrastructure, and government organizations such as the military.
Internet Service Provider (ISP): An organization that provides IP Internet Service Provider (ISP): An organization that provides IP
network-layer services to its customers or users. This entity may network-layer services to its customers or users. This entity may
or may not provide the physical-layer and layer-2 connectivity, or may not provide the physical-layer and data link (layer-2)
such as fiber or Ethernet, i.e., it may or may not be the role of connectivity, such as fiber or Ethernet, i.e., it may or may not
an IAP. play the role of an IAP.
Application Service Provider (ASP): The organization or entity that Application Service Provider (ASP): The organization or entity that
provides application-layer services, which may include voice (see provides application-layer services, which may include voice (see
"Voice Service Provider"). This entity can be a private "Voice Service Provider"). This entity can be a private
individual, an enterprise, a government, or a service provider. individual, an enterprise, a government, or a service provider.
An ASP is more general than a Voice Service Provider, since An ASP is more general than a Voice Service Provider, since
emergency calls may use other media beyond voice, including text emergency calls may use other media beyond voice, including text
and video. For a particular user, the ASP may or may not be the and video. For a particular user, the ASP may or may not be the
same organization as his IAP or ISP. same organization as his IAP or ISP.
Voice Service Provider (VSP): A specific type of Application Service Voice Service Provider (VSP): A specific type of Application Service
Provider which provides voice related services based on IP, such Provider which provides voice related services based on IP, such
as call routing, a SIP URI, or PSTN termination. In this as call routing, a SIP URI, or PSTN termination. In this
document, unless noted otherwise, any reference to "Voice Service document, unless noted otherwise, any reference to "Voice Service
Provider" or "VSP" may be used interchangeably with "Application/ Provider" or "VSP" may be used interchangeably with "Application/
Voice Service Provider" or "ASP/VSP". Voice Service Provider" or "ASP/VSP".
3.3 Actors
(Emergency) caller: The term "caller" or "emergency caller" refer to
the person placing an emergency call or sending an emergency
instant message (IM).
User Equipment (UE): User equipment is the device or software
operated by the caller to place an emergency call. A SIP user
agent (UA) is an example of a UE.
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
caller and thus do not concern us here.
3.4 Call Routing Entities
Emergency Service Routing Proxy (ESRP): An ESRP is an emergency call Emergency Service Routing Proxy (ESRP): An ESRP is an emergency call
routing support entity that invokes the location-to-PSAP URI routing support entity that invokes the location-to-PSAP URI
mapping, to return either the URI for the appropriate PSAP, or the mapping, to return either the URI for the appropriate PSAP, or the
URI for another ESRP. (In a SIP system, the ESRP would typically URI 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 be a SIP proxy, but may also be a back-to-back user agent
(B2BUA)). (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 Public Safety Answering Point (PSAP): Physical location where
emergency calls are received under the responsibility of a public emergency calls are received under the responsibility of a public
authority. (This terminology is used by both ETSI, in ETSI SR 002 authority. (This terminology is used by both ETSI, in ETSI SR 002
180, and NENA.) In the United Kingdom, PSAPs are called Operator 180, and NENA.) In the United Kingdom, PSAPs are called Operator
Assistance Centres, in New Zealand, Communications Centres. Assistance Centres, in New Zealand, Communications Centres.
Within this document, it is assumed, unless stated otherwise, that Within this document, it is assumed, unless stated otherwise, that
PSAP is that which supports the receipt of emergency calls over PSAPs support the receipt of emergency calls over IP, using
IP. It is also assumed that the PSAP is reachable by IP-based appropriate application layer protocols such as SIP for call
protocols, such as SIP for call signaling and RTP for media. signaling and RTP for media.
3.5 Location
Location: A geographic identification assigned to a region or feature Location: A geographic identification assigned to a region or feature
based on a specific coordinate system, or by other precise based on a specific coordinate system, or by other precise
information such as a street number and name. It can be either a information such as a street number and name. It can be either a
civic or geographic location. civic or geographic location.
Civic location: A described location based on some defined grid, such Civic location: A described location based on some reference system,
as a jurisdictional, postal, metropolitan, or rural reference such as jurisdictional region or postal delivery grid. A street
system, (e.g., street address). address is a common example of a civic location.
Geographic location: A reference to a point which is able to be Geographic location: A reference to a point which is able to be
located as described by a set of defined coordinates within a located as described by a set of defined coordinates within a
geographic coordinate system, (e.g., lat/lon within the WGS-84 geographic coordinate system, such as latitude and longitude
datum). For example, (2-D) geographic location is defined as an within the WGS-84 datum. For example, 2-D geographic location is
x,y coordinate value pair according to the distance North or South defined as an (x,y) coordinate value pair according to the
of the equator and East or West of the prime meridian. 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 Location validation: A caller location is considered valid if the
civic or geographic location is recognizable within an acceptable civic or geographic location is recognizable within an acceptable
location reference system (e.g., USPS, WGS-84, etc.), and can be location reference system (e.g., United States Postal Address or
mapped to one or more PSAPs. While it is desirable to determine the WGS-84 datum) and can be mapped to one or more PSAPs. While
that a location exists, validation may not ensure that such a it is desirable to determine that a location exists, validation
location exists, but rather may only ensure that the location may not ensure that such a location exists, but rather may only
falls within some range of known values. Location validation ensure that the location falls within some range of known values.
ensures that a location is able to be referenced for mapping, but Location validation ensures that a location is able to be
makes no assumption about the association between the caller and referenced for mapping, but makes no assumption about the
the caller's location. association between the caller and the caller's location.
(Location-dependent) emergency dial string: A location-dependent 3.6 Identifiers, Numbers and Dial Strings
emergency dial string should be thought of as the digit sequence
that is dialed in order to reach emergency services. There are
two dial strings described within this document, namely a "home
emergency dial string", and a "visited emergency dial string".
Home emergency dial string: A home emergency dial string represents a (Emergency) service number: The (emergency) service number is a
(e.g., dialed) sequence of digits, that is used to initiate an string of digits used to reach the (emergency) service. The
emergency call within a geographically correct location of a emergency service number is often just called the emergency
caller if it is considered to be a user's "home" location or number. It is the number typically dialed on devices directly
vicinity. connected to the PSTN and the number reserved for emergency calls
by national or regional numbering authorities. It only contains
the digits 0 through 9, # and *. The service number may depend on
the location of the caller. For example, the general emergency
service number in the United States is 911 and the poison control
service number is 18002221222. In most cases, the service number
and dial string are the same; they may differ in some private
phone networks. A service number may be carried in tel URLs [7],
along with a context identifier. In the North American numbering
plan, some service numbers are also three-digit N11 or service
codes, but not all emergency numbers have three digits. A caller
may have to dial a service dial string (below) that differs from
the service number when using a PBX.
Visited emergency dial string: A visited emergency dial string (Emergency) service dial string: The service dial string identifies
represents a sequence of digits that is used to initiate an the string of digits that a caller must dial to reach a particular
emergency call within a geographically correct location of the (emergency) service. In devices directly connected to the PSTN,
caller if outside the caller's "home" location or vicinity. the service dial string is the same as the service number and may
thus depend on the location of the caller. However, in private
phone networks, such as in PBXs, the service dial string consists
of a dialing prefix to reach an outside line, followed by the
emergency number. For example, in a hotel, the dial string for
emergency services in the United States might be 9911. Dial
strings may contain indications of pauses or wait-for-secondary-
dial-tone indications. Service dial strings are outside the scope
of this document.
Service identifier: A general identifier that has applicability to (Emergency) service identifier: The (emergency) service identifier
both emergency and non-emergency contexts (specifically referred describes the emergency service, independent of the user interface
to within this document as "emergency service identifier"). mechanism, the signaling protocol that is used to reach the
service, or the caller's geographic location. It is a protocol
constant and used within the mapping and signaling protocols. An
example is the service URN [12].
Service URN: An implementation of a service identifier, which has (Emergency) service URL: The service URL is a protocol-specific
applicability to both emergency and non-emergency contexts (e.g., (e.g., SIP) or protocol-agnostic (e.g., im: [6]) contains the
urn:service:sos, urn:service:info, etc.) Within this document, address of the PSAP or other emergency service. It depends on the
service URN is specifically referred to as 'emergency service URN' specific signaling or data transport protocol used to reach the
[8]. emergency service.
Emergency service identifier (ESI): A specific service identifier Service URN: A service URN is an implementation of a service
that is used to request a PSAP URI in order to initiate an identifier, which can be applied to both emergency and non-
emergency call, and may be used to mark any call as an emergency emergency contexts, e.g., urn:service:sos or
call. An ESI is a more general term than 'emergency service URN', urn:service:counseling. Within this document, service URNs are
since it could also refer to an alternate identifier, such as a referred to as 'emergency service URNs' [12].
tel URI (Section 6).
Emergency service URN: An emergency-context specific service URN that Home emergency number: A home emergency number is the emergency
is an implementation of an emergency service identifier (e.g., number valid at the caller's customary home location, e.g., his
urn:service:sos). Is often referred to as, and is equivalent with permanent residence. The home location may or may not coincide
'sos service URN'. with the service area of the caller's VSP.
PSAP URI: The URI (e.g., SIP:URI, SIPS:URI, XMPP:URI, etc.) at which Home emergency dial string: A home dial string is the dial string
the PSAP may be contacted with an emergency call. This contact valid at the caller's customary home location, e.g., his permanent
could be done directly, or via an intermediary, (e.g., ESRP). residence.
Mapping: The process of resolving a location to one or more PSAP URIs Visited emergency number: A visited emergency number is the emergency
which directly identify a PSAP, or point to an intermediary which number valid at the caller's current physical location. We
knows about a PSAP and that is designated as responsible to serve distinguish the visited emergency number if the caller is
that location. traveling outside his home region.
Visited emergency dial string: A visited emergency dial string is the
dial string number valid at the caller's current physical
location.
3.7 Mapping
Mapping: Mapping is 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 for serving that location.
Mapping client: A mapping client interacts with the mapping server to Mapping client: A mapping client interacts with the mapping server to
learn one or more PSAP URIs for a given location. learn one or more PSAP URIs for a given location.
Mapping protocol: A protocol used to convey the mapping request and Mapping protocol: A protocol used to convey the mapping request and
response. response.
Mapping server: The mapping server holds information about the Mapping server: The mapping server holds information about the
location-to-PSAP URI mapping. location-to-PSAP URI mapping.
Mapping service: A network service which uses a distributed mapping Mapping service: A network service which uses a distributed mapping
protocol to perform a mapping between a location and a PSAP, or protocol to perform a mapping between a location and a PSAP, or
intermediary which knows about the PSAP, and is used to assist in intermediary which knows about the PSAP, and is used to assist in
routing an emergency call. routing an emergency call.
(Emergency) caller: The term "caller" or "emergency caller" refer to 4. Basic Actors
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.
3. Basic Actors
In order to support emergency services covering a large physical In order to support emergency services covering a large physical
area, various infrastructure elements are necessary, including: area, various infrastructure elements are necessary, including
Internet Attachment Providers (IAPs), Application/Voice Service Internet Attachment Providers (IAPs), Application/Voice Service
Providers (ASP/VSPs), Emergency Call Routing Support (ECRS) Providers (ASP/VSPs), Emergency Service Routing Proxy (ESRP)
providers, mapping service providers, and PSAPs. providers, mapping service providers, and PSAPs.
This section outlines which entities will be considered in the This section outlines which entities will be considered in the
routing scenarios discussed. routing scenarios discussed.
Location Location
Information +-----------------+ Information +-----------------+
|(1) |Internet | +-----------+ |(1) |Internet | +-----------+
v |Attachment | | | v |Attachment | | |
+-----------+ |Provider | | Mapping | +-----------+ |Provider | | Mapping |
| | | (3) | | Service | | | | (3) | | Service |
| Emergency |<---+-----------------+-->| | | Emergency |<---+-----------------+-->| |
| Caller | | (2) | +-----------+ | Caller | | (2) | +-----------+
| |<---+-------+ | ^ | |<---+-------+ | ^
+-----------+ | +----|---------+------+ | +-----------+ | +----|---------+------+ |
^ | | Location | | | ^ | | Location | | |
| | | Information<-+ | | | | | Information<-+ | |
| +--+--------------+ |(5) | | (6) | +--+--------------+ |(5) | | (6)
| | | | | | | | | |
| | +-----------v+ | | | | +-----------v+ | |
| (4) | |Emergency | | | | (4) | | | | |
+--------------+--->|Call Routing|<--+---+ +--------------+--->| ESRP |<--+---+
| | |Support | | | | | | |
| | +------------+ | | | +------------+ |
| | ^ | | | ^ |
| | (7) | | +----+--+ | | (7) | | +----+--+
| (8) | +------------>| | | (8) | +------------>| |
+--------------+----------------------->| PSAP | +--------------+----------------------->| PSAP |
| | | | | | | |
|Application/ | +----+--+ |Application/ | +----+--+
|Voice | |Voice |
|Service | |Service |
|Provider | |Provider |
+---------------------+ +---------------------+
Figure 1: Framework for emergency call routing Figure 1: Framework for emergency call routing
Figure 1 shows the interaction between the entities involved in the Figure 1 shows the interaction between the entities involved in the
call. There are a number of different deployment choices, as can be call. There are a number of different deployment choices, as can be
easily seen from the figure. easily seen from the figure.
o How is location information provided to the end host? It might How is location information provided to the end host? It might
either be known to the end host itself via manual configuration, either be known to the end host itself via manual configuration,
provided via GPS, made available via DHCP (RFC 3825 [4]) or some provided via GPS, made available via DHCP ([5], [14]) or some other
other mechanisms. Alternatively, location information is used as mechanism. Alternatively, location information is inserted by
part of call routing and inserted by intermediaries. intermediaries.
o Is the Internet Attachment Provider also the Application/Voice Is the Internet Attachment Provider also the Application/Voice
Service Provider? In the Internet today these roles are typically Service Provider? In the Internet today these roles are typically
provided by different entities. As a consequence, the Application/ provided by different entities. As a consequence, the Application/
Voice Service Provider is typically not able to learn the physical Voice Service Provider is typically not able to directly determine
location of the emergency caller. the physical location of the emergency caller.
The overlapping squares in the figure indicate that some functions The overlapping squares in the figure indicate that some functions
can be collapsed into a single entity. As an example, the can be collapsed into a single entity. As an example, the
Application/Voice Service Provider might be the same entity as the Application/Voice Service Provider might be the same entity as the
Internet Attachment Provider. There is, however, no requirement that Internet Attachment Provider. There is, however, no requirement that
this must be the case. Additionally, we consider that end systems 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 might act as their own ASP/VSP, e.g., either for enterprises or for
residential users. residential users.
Various potential interactions between the entities depicted in Various potential interactions between the entities depicted in
Figure 1, are described in the following: Figure 1 are described below:
(1) Location information might be available to the end host itself. 1. Location information might be available to the end host itself.
(2) Location information might, however, also be obtained from the 2. Location information might, however, also be obtained from the
Internet Attachment Provider (e.g., using DHCP or application layer Internet Attachment Provider (e.g., using DHCP or application
signaling protocols). layer signaling protocols).
(3) The emergency caller might need to consult a mapping service to 3. The emergency caller might need to consult a mapping service to
determine the PSAP (or other relevant information) that is determine the PSAP (or other relevant information) that is
appropriate for the physical location of the emergency caller, appropriate for the physical location of the emergency caller,
possibly considering other attributes such as appropriate language possibly considering other attributes such as appropriate
support by the emergency call taker. language support by the emergency call taker.
(4) The emergency caller might get assistance for emergency call 4. The emergency caller might get assistance for emergency call
routing by infrastructure elements that are emergency call routing routing by infrastructure elements that are emergency call
support entities, (e.g., an Emergency Service Routing Proxy (ESRP), routing support entities, such as an Emergency Service Routing
in SIP). Proxy (ESRP) in SIP.
(5) Location information is used by emergency call routing support 5. Location information is used by emergency call routing support
entities for subsequent mapping requests. entities for subsequent mapping requests.
(6) Emergency call routing support entities might need to consult a 6. Emergency call routing support entities might need to consult a
mapping service to determine where to route the emergency call. mapping service to determine where to route the emergency call.
(7) For infrastructure-based emergency call routing (in contrast to 7. For infrastructure-based emergency call routing (in contrast to
UE-based emergency call routing), the emergency call routing support UE-based emergency call routing), the emergency call routing
entity needs to forward the call to the PSAP. support entity needs to forward the call to the PSAP.
(8) The emergency caller (UE) may interact directly with the PSAP 8. The emergency caller may interact directly with the PSAP, where
(e.g., UE invokes mapping, and initiates a connection), without the UE invokes mapping, and initiates a connection, without
relying on any intermediary emergency call routing support entities. relying on any intermediary emergency call routing support
entities.
4. High-Level Requirements 5. High-Level Requirements
Below, we summarize high-level architectural requirements that guide Below, we summarize high-level architectural requirements that guide
some of the component requirements detailed later in the document. some of the component requirements detailed later in the document.
Re1. Application/Voice service provider existence: The initiation of Re1. Application/Voice service provider existence: The initiation of
an IP-based emergency call SHOULD NOT assume the existence of an an IP-based emergency call SHOULD NOT assume the existence of an
Application/Voice Service Provider (ASP/VSP). Application/Voice Service Provider (ASP/VSP).
Motivation: The caller may not have an application/voice service Motivation: The caller may not have an application/voice service
provider. For example, a residence may have its own DNS domain provider. For example, a residence may have its own DNS domain
and run its own SIP proxy server for that domain. On a larger and run its own SIP proxy server for that domain. On a larger
scale, a university might provide voice services to its students scale, a university might provide voice services to its students
and staff, but might not be a telecommunication provider. and staff, but might not be a telecommunication provider.
Re2. International applicability: Regional, political and Re2. International applicability: Regional, political and
organizational aspects MUST be considered during the design of organizational aspects MUST be considered during the design of
protocols and protocol extensions which support IP-based emergency protocols and protocol extensions which support IP-based emergency
calls. calls.
Motivation: It must be possible for a device or software developed Motivation: It must be possible for a device or software developed
or purchased in one country to place emergency calls in another or purchased in one country to place emergency calls in another
country. System components should not be biased towards a country. System components should not be biased towards a
particular set of emergency numbers or languages. Also, different particular set of emergency numbers or languages. Also, different
countries have evolved different ways of organizing emergency countries have evolved different ways of organizing emergency
services, e.g., either centralizing them or having smaller services, e.g., either centralizing them or having smaller
regional subdivisions such as United States counties or regional subdivisions such as United States counties or
municipalities which handle emergency calls. municipalities handle emergency calls within their jurisdiction.
Re3. Distributed administration: Deployment of IP-based emergency Re3. Distributed administration: Deployment of IP-based emergency
services MUST NOT depend on a sole central administration services MUST NOT depend on a single central administrative
authority. authority.
Motivation: The design of the mapping protocol must make it Motivation: The design of the mapping protocol must make it
possible to deploy and administer emergency calling features on a possible to deploy and administer emergency calling features on a
regional or national basis without requiring coordination with regional or national basis without requiring coordination with
other regions or nations. The system cannot assume, for example, other regions or nations. The system cannot assume, for example,
that there is a single global entity issuing certificates for that there is a single global entity issuing certificates for
PSAPs, ASP/VSPs, IAPs or other participants. PSAPs, ASP/VSPs, IAPs or other participants.
Re4. Multi-mode communication: IP-based emergency calls MUST support Re4. Multi-mode communication: IP-based emergency calls MUST support
multiple communication modes, including, for example, audio, video multiple communication modes, including, for example, audio, video
and text. and text.
Motivation: Within the PSTN, voice and text telephony (often Motivation: Within the PSTN, voice and text telephony (often
called TTY or text-phone in North America) are the only commonly called TTY or text-phone in North America) are the only commonly
supported media. Emergency calling must support a variety of supported media. Emergency calling must support a variety of
media. Such media should include voice, conversational text (RFC media. Such media should include voice, conversational text (RFC
4103 [5]), instant messaging and video. 4103 [8]), 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 Re5. Mapping result usability: The mapping protocol MUST return one
or more URIs that are usable within a standard signaling protocol or more URIs that are usable within a standard signaling protocol
(i.e., without special emergency extensions). (i.e., without special emergency extensions).
Motivation: For example, a SIP specific URI which is returned by Motivation: For example, a SIP URI which is returned by the
the mapping protocol needs to be usable by any SIP capable phone mapping protocol needs to be usable by any SIP capable phone
within a SIP initiated emergency call. This is in contrast to a within a SIP initiated emergency call. This is in contrast to a
"special purpose" URI, which may not be recognizable by a legacy "special purpose" URI, which may not be recognizable by a legacy
SIP device. SIP device.
Re8. PSAP URI accessibility: The mapping protocol MUST support Re6. PSAP URI accessibility: The mapping protocol MUST support
interaction between the client and server where no enrollment to a interaction between the client and server where no enrollment to a
mapping service exists or is required. mapping service exists or is required.
Motivation: The mapping server may well be operated by a service Motivation: The mapping server may well be operated by a service
provider, but access to the server offering the mapping must not provider, but access to the server offering the mapping must not
require use of a specific ISP or ASP/VSP. require use of a specific ISP or ASP/VSP.
Re9. Common data structures and formats: The mapping protocol SHOULD Re7. Common data structures and formats: The mapping protocol SHOULD
support common data structures and formats from the mapping support common formats for location data.
server.
Motivation: Location databases should not need to be transformed Motivation: Location databases should not need to be transformed
or modified in any unusual or unreasonable way in order for the or modified in any unusual or unreasonable way in order for the
mapping protocol to use the data. For example, a database which mapping protocol to use the data. For example, a database which
contains civic addresses used by location servers may be used for contains civic addresses used by location servers may be used for
multiple purposes and applications beyond emergency service multiple purposes and applications beyond emergency service
location-to-PSAP URI mapping. location-to-PSAP URI mapping.
Re10. Anonymous mapping: The mapping protocol MUST NOT require the Re8. Anonymous mapping: The mapping protocol MUST NOT require the
true identity of the target for which the location information is true identity of the target for which the location information is
attributed. attributed.
Motivation: Ideally, no identity information is provided via the Motivation: Ideally, no identity information is provided via the
mapping protocol. Where identity information is provided, it may mapping protocol. Where identity information is provided, it may
be in the form of an unlinked pseudonym (RFC 3693 [3]). be in the form of an unlinked pseudonym (RFC 3693 [4]).
5. Identifying the Caller's Location 6. Identifying the Caller's Location
Location can either be provided directly, or by reference, and Location can either be provided directly (by value), or via a poiner
represents either a civic location, or a geographic location. An (by reference), and represents either a civic location, or a
important question is how and when to attach location information to geographic location. An important question is how and when to attach
the VoIP emergency signaling. In general, we can distinguish three location information to the VoIP emergency signaling messages. In
modes of operation of how a location is associated with an emergency general, we can distinguish three modes of operation of how a
call: location is associated with an emergency call:
UA-inserted: The caller's user agent inserts the location information UA-inserted: The caller's user agent inserts the location information
into the call signaling message. The location information is into the call signaling message. The location information is
derived from sources such as GPS, DHCP (see [4] for geographic derived from sources such as GPS, DHCP (see [5] for geographic
location information and [10]) for civic location information or location information and [14] for civic location information) or
utilizing the Link Layer Discovery Protocol (LLDP) [see utilizing the Link Layer Discovery Protocol (LLDP) [16].
IEEE8021AB].
UA-referenced: The caller's user agent provides a pointer (i.e., a UA-referenced: The caller's user agent provides a pointer (i.e., a
location reference), via a permanent or temporary identifier, to location reference), via a permanent or temporary identifier, to
the location which is stored by a location server somewhere else the location information, which is stored by a location server
and then retrieved by the PSAP, ESRP, or other authorized service somewhere else and then retrieved by the PSAP, ESRP, or other
entity. authorized entity.
Proxy-inserted: A proxy along the call path inserts the location or Proxy-inserted: A proxy along the call path inserts the location or
location reference. location reference.
The following requirements apply:
Lo1. Reference datum: The mapping protocol MUST support the WGS-84 Lo1. Reference datum: The mapping protocol MUST support the WGS-84
coordinate reference system and MAY support other coordinate coordinate reference system and MAY support other coordinate
reference systems. reference systems.
Motivation: Though many different datums exist around the world, Motivation: Though many different datums exist around the world,
the WGS-84 datum is recommended here since it is designed to this document recommends the WGS-84 datum since it is designed to
describe the whole earth, rather than a single continent, etc. describe the whole earth, rather than a single continent or other
region, and is commonly used to represent Global Positioning
Lo2. Location object/info preservation: The mapping protocol MUST System coordinates.
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 Lo2. Location delivery by-value: The mapping protocol MUST support
the delivery of location information using a by-value method, the delivery of location information using a by-value method,
though it MAY also support de-referencing a URL that references a though it MAY also support de-referencing a URL that references a
location object. location object.
Motivation: The mapping protocol is not required to support the Motivation: The mapping protocol is not required to support the
ability to de-reference specific location references. ability to de-reference specific location references.
Lo4. Alternate community names: The mapping protocol MUST support Lo3. Alternate community names: The mapping protocol MUST support
both the jurisdictional community name and the postal community both the jurisdictional community name and the postal community
name fields within the PIDF-LO data. name fields within the PIDF-LO [9] data.
Motivation: A mapping query must be accepted with either or both Motivation: The mapping protocol must accept queries with either
community name fields, and provide appropriate responses. If a a postal or jurisdictional community name field, or both, and
mapping query is made with only one field present, and if the provide appropriate responses. If a mapping query contains only
database contains both jurisdictional and postal, the mapping one community name and the database contains both jurisdictional
protocol response should return both. and postal community names, the mapping protocol response SHOULD
return both community names.
Lo5. Validation of civic location: The mapping protocol MUST support Lo4. Validation of civic location: The mapping protocol MUST support
location validation for civic location (street addresses). location validation for civic locations (street addresses).
Motivation: Location validation provides an opportunity to help Motivation: Location validation provides an opportunity to help
assure ahead of time, whether or not a successful mapping to the ascertain ahead of time whether or not a successful mapping to the
appropriate PSAP will likely occur when it is required. appropriate PSAP will likely occur when it is required.
Validation may also help to avoid delays during emergency call Validation may also help to avoid delays during emergency call
setup due to invalid locations. setup due to invalid location data.
Lo6. Validation resolution: The mapping protocol MUST support the Lo5. Validation resolution: The mapping protocol MUST support the
ability to provide ancillary information about the resolution of ability to provide ancillary information about the resolution of
location data used to retrieve a PSAP URI. location data used to retrieve a PSAP URI.
Motivation: The mapping server may not use all the data elements Motivation: The mapping server may not use all the data elements
in the provided location information to determine a match, or may 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 be able to find a match based on all of the information except for
some specific data elements. The uniqueness of this information some specific data elements. The uniqueness of this information
set may be used to differentiate among emergency jurisdictions. set may be used to differentiate among emergency jurisdictions.
Precision or resolution in the context of this requirement might Precision or resolution in the context of this requirement might
mean, for example, explicit identification of the data elements mean, for example, explicit identification of the data elements
that were used successfully in the mapping. that were used successfully in the mapping.
Lo7. Indication of non-existent location: The mapping protocol MUST Lo6. Contact for location problems: The mapping protocol MUST
support a mechanism to indicate and resolve any associated issues support a mechanism to contact an appropriate authority to resolve
attributed to a location or a part of a location that is known to mapping-related issues for the queried location. For example, the
not exist, despite the receipt of a successful mapping response. querier may want to report problems with the response values or
indicate that the mapping database is mistaken on declaring a
civic location as non-existent.
Motivation: The emergency authority for a given jurisdiction may Motivation: Initially, authorities may provide URLs where a human
provide a means to resolve addressing problems, e.g., a URI for a user can report problems with an address or location. In
web service that can be used to report problems with an address. addition, web services may be defined to automate such reporting.
For example, the querier may wish to report that the mapping
database may be missing a newly-built or renamed street or house
number.
Lo8. Limits to validation: Successful validation of a civic location Lo7. Limits to validation: Successful validation of a civic location
MUST NOT be required to place an emergency call. MUST NOT be required to place an emergency call.
Motivation: In some cases, a civic location may not be considered Motivation: In some cases, a civic location may not be considered
valid. This fact should not result in the call being dropped or valid. This fact should not result in the call being dropped or
rejected by any entity along the call setup signaling path to the rejected by any entity along the call setup signaling path to the
PSAP. PSAP.
Lo9. 3D sensitive mapping: The mapping protocol MUST implement Lo8. 3D sensitive mapping: The mapping protocol MUST implement
support for both 2D and 3D location information, and may accept support for both 2D and 3D location information, and may accept
either a 2D or 3D mapping request as input. either a 2D or 3D mapping request as input.
Motivation: It is expected that end devices or location servers Motivation: It is expected that queriers may provide either 2D or
will provide either 2D or 3D data. When a 3D request is presented 3D data. When a 3D request is presented within an area only
within an area only defined by 2D data within the mapping server, defined by 2D data within the mapping server, the mapping result
the mapping result would be the same as if the height/altitude would be the same as if the height or altitude coordinate had been
dimension was omitted in the request. omitted from the mapping request.
Lo10. Database type indicator: The mapping protocol MAY support a Lo9. Database type indicator: The mapping protocol MAY support a
mechanism which provides an indication describing a specific mechanism which provides an indication describing a specific type
"type" of location database used. of location database used.
Motivation: It is useful to know the source of the data stored in Motivation: It is useful to know the source of the data stored in
the database used for location validation. This is applicable for the database used for location validation, either for civic or
either civic or geographic location matching (e.g., USPS, MSAG, geographic location matching. In the United States, sources of
GDT, etc.). data could include the United States Postal Service, the Master
Street Address Guide (MSAG) or commercial map data providers.
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 7. Emergency Service Identifier
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" (ESI) 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 Emergency service identifiers are protocol constants that allow
be able to return one or multiple emergency service identifiers in protocol entities such as SIP proxy servers to distinguish emergency
response to a query. calls from non-emergency calls and to identify the specific emergency
service desired. Emergency service identifiers are a subclass of
service identifiers that more generally identify services reachable
by callers. An example of a service identifier is the service URN
[12], but other identifiers, such as tel URIs [7], may also serve
this role during a transition period.
Motivation: Since there is a need for any device or network Since this document only addresses emergency services, we use the
element to recognize an emergency call throughout the call setup, terms "emergency service identifier" and "service identifier"
there is also a need to have the mapping protocol provide support interchangeably. Requirements for these identifiers include:
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 Id1. Multiple emergency services: The mapping protocol MUST be able
emergency service identifiers exist, the mapping protocol MUST be to distinguish between different emergency services,
able to differentiate between ESIs based on the specific type of differentiated by different service identifiers.
emergency help requested.
Motivation: Some jurisdictions may have multiple types of Motivation: Some jurisdictions may offer multiple types of
emergency services available, (e.g., fire, police, ambulance), in emergency services that operate independently and can be contacted
which case, it is important that any one could be selected directly, for example, fire, police and ambulance services.
directly.
Id3. Extensible emergency service identifiers: The mapping protocol Id2. Extensible emergency service identifiers: The mapping protocol
MUST support an extensible list of emergency identifiers, though MUST support an extensible list of emergency identifiers, though
it is not required to provide mapping for every possible service. it is not required to provide mappings for every possible service.
Motivation: The use of an emergency service identifier is locally Motivation: Extensibility is required since new emergency
determined. services may be introduced over time, either globally or in some
jurisdictions. The availability of emergency services depends on
the locations. For example, the Netherlands are unlikely to offer
a mountain rescue service.
Id4. Discovery of emergency dial string: There MUST be support for a Id3. Discovery of emergency number: The mapping protocol MUST be
mechanism to discover an existing location-dependent emergency able to return the location-dependent emergency number for the
dial string, (e.g., "9-1-1", "1-1-2"), contextually appropriate location indicated in the query.
for the location of the caller.
Motivation: Users are trained to dial the appropriate emergency Motivation: Users are trained to dial the appropriate emergency
dial string to reach emergency services. There needs to be a way number to reach emergency services. There needs to be a way to
to figure out what the dial string is within the local environment figure out the emergency number at the current location of the
of the caller. caller.
Id5. Home emergency dial string translation: There MUST be support Id4. Home emergency number recognition: User equipment MUST be able
for end device translation (e.g., SIP UA) of a home emergency dial to translate a home emergency number into an emergency service
string into an emergency service identifier. identifier.
Motivation: The UA would most likely be pre-provisioned with the Motivation: The UE could be pre-provisioned with the appropriate
appropriate information in order to make such a translation. The information in order to perform such a translation or could
mapping protocol would be able to support either type for those discover the emergency number by querying the mapping protocol
clients which may not support dial string translation. with its home location.
Id6. Emergency dial string replacement: There SHOULD be support for Id5. Emergency number replacement: There SHOULD be support for
replacement of the original dial string with a reserved emergency replacement of the emergency number with the appropriate emergency
service identifier for each signaling protocol used for an service identifier for each signaling protocol used for an
emergency call. This replacement of the original dial string emergency call, based on local conventions, regulations, or
should be based on local conventions, regulations, or preference preference (e.g., as in the case of an enterprise).
(e.g., as in the case of an enterprise).
Motivation: Any signaling protocol requires the use of some Motivation: Any signaling protocol requires the use of some
identifier to indicate the called party, and the user terminal may identifier to indicate the called party, and the user equipment
lack the capability to determine the actual emergency address may lack the capability to determine the actual service URL (PSAP
(PSAP URI). The use of local conventions may be required as a URI). The use of local conventions may be required as a
transition mechanism. Note: Such use complicates international transition mechanism. Since relying on recognizing local
movement of the user terminal. Evolution to a standardized numbering conventions makes it difficult for devices to be used
emergency service identifier or set of identifiers is preferred. outside their home context and for external devices to be
introduced into a network, protocols should use standardized
emergency service identifiers.
Id7. Emergency service identifier marking: There MUST be support for Id6. Emergency service identifier marking: Signaling protocols MUST
an emergency service identifier to be used for marking the call as support emergency service identifiers to mark a call as an
an emergency call. emergency call.
Motivation: Marking ensures proper handling as an emergency call Motivation: Marking ensures proper handling as an emergency call
by downstream elements that may not recognize, for example, a by downstream elements that may not recognize, for example, a
local variant of a logical emergency address, etc. This marking local variant of a logical emergency address. This marking
mechanism is assumed to be different than a QoS marking mechanism. mechanism is related to, but independent of, marking calls for
prioritized call handling [10].
Id8. Emergency service identifier not recognized: There MUST be Id7. Handling unrecognized emergency service identifiers: There MUST
support for calls which are initiated as emergency calls even if be support for calls which are initiated as emergency calls even
the specific emergency service requested is not recognized, based if the specific emergency service requested is not recognized by
on the emergency service identifier used. the ESRP. Such calls will then be routed to a generic emergency
service.
Motivation: In order to have a robust system that supports Motivation: Fallback routing allows new emergency services to be
incremental service deployment while still maintaining a fallback introduced incrementally, while avoiding non-routable emergency
capability. calls. For example, a call for marine rescue services would be
routed to a general PSAP if the caller's location does not offer
marine rescue services yet.
Id9. Discovery of visited emergency dial strings: There MUST be Id8. Return fallback service identifier: The mapping protocol must
support for a mechanism to allow the end device to learn visited be able to report back the actual service mapped if the mapping
emergency dial strings. protocol substitutes another service for the one requested.
Motivation: Scenarios exist where a user dials a visited emergency Motivation: A mapping server may be configured to automatically
dial string that is different from the home emergency dial string: look up the PSAP for another service if the user-requested service
If a user (i.e., UA operator) visits a foreign country, observes a is not available for that location. For example, if there is no
fire truck with 999 on the side, the expectation is one of being marine rescue service, the mapping protocol might return the PSAP
able to dial that same number to summon a fire truck. Another use URL for general emergencies and include the "urn:service.sos"
case cited is where a tourist collapses, and a "good Samaritan" identifier in the response to alert the querier to that fact.
uses the tourist's cell phone to enter a home emergency dial
string appropriate for that foreign country.
7. Mapping Protocol Id9. Discovery of visited emergency dial strings: There MUST be a
mechanism to allow the end device to learn visited emergency
numbers.
Motivation: Travelers visiting a foreign country may observe the
local emergency number, e.g., seeing it painted on the side of a
fire truck, and then rightfully expect to be able to dial that
emergency number. Similarly, a local "good Samaritan" may use a
tourist's cell phone to summon help.
8. Mapping Protocol
There are two basic approaches to invoke the mapping protocol. We There are two basic approaches to invoke the mapping protocol. We
refer to these as caller-based and mediated. In each case, the refer to these as caller-based and mediated. In each case, the
mapping client initiates a request to a mapping server via a mapping mapping client initiates a request to a mapping server via a mapping
protocol. A proposed mapping protocol is outlined in the document protocol. A proposed mapping protocol, LoST, is outlined in [13].
I-D.hardie-ecrit-lost [9].
For caller-based resolution, the caller's user agent invokes the For caller-based resolution, the caller's user agent invokes the
mapping protocol to determine the appropriate PSAP based on the mapping protocol to determine the appropriate PSAP based on the
location provided. The resolution may take place well before the location provided. The resolution may take place well before the
actual emergency call is placed, or at the time of the call. actual emergency call is placed, or at the time of the call.
For mediated resolution, an emergency call routing support entity, For mediated resolution, an emergency call routing support entity,
such as a SIP (outbound) proxy or redirect server invokes the mapping such as a SIP (outbound) proxy or redirect server invokes the mapping
service. service.
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Motivation: An over-abundance of similarly-capable choices appears Motivation: An over-abundance of similarly-capable choices appears
undesirable for interoperability. undesirable for interoperability.
Ma2. Extensible protocol: The mapping protocol MUST be designed to Ma2. Extensible protocol: The mapping protocol MUST be designed to
support the extensibility of location data elements, both for new support the extensibility of location data elements, both for new
and existing fields. and existing fields.
Motivation: This is needed, for example, to accommodate future Motivation: This is needed, for example, to accommodate future
extensions to location information that might be included in the extensions to location information that might be included in the
PIDF-LO ([6]). PIDF-LO ([9]).
Ma3. Incrementally deployable: The mapping protocol MUST be designed Ma3. Incrementally deployable: The mapping protocol MUST be designed
in such a way that supports the incremental deployment of mapping to support its incremental deployment.
services.
Motivation: It must not be necessary, for example, to have a Motivation: It must not be necessary, for example, to have a
global street level database before deploying the system. It is global street level database before deploying the system. It is
acceptable to have some misrouting of calls when the database does acceptable to have some misrouting of calls when the database does
not (yet) contain accurate PSAP service area information. not (yet) contain accurate PSAP service area information.
Ma4. Any time mapping: The mapping protocol MUST support the ability Ma4. Any time mapping: The mapping protocol MUST support the ability
of the mapping function to be invoked at any time, including while of the mapping function to be invoked at any time, including while
an emergency call is in process and before an emergency call is an emergency call is in process and before an emergency call is
initiated. initiated.
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also result in inefficient use of PSAP resources at the initial also result in inefficient use of PSAP resources at the initial
point of contact. It is important that the location determination point of contact. It is important that the location determination
mechanism not be fooled by the location of IP telephony gateways mechanism not be fooled by the location of IP telephony gateways
or dial-in lines into a corporate LAN (and dispatch emergency help or dial-in lines into a corporate LAN (and dispatch emergency help
to the gateway or campus, rather than the caller), multi-site LANs to the gateway or campus, rather than the caller), multi-site LANs
and similar arrangements. and similar arrangements.
Ma7. Multiple PSAP URIs: The mapping protocol MUST support a method Ma7. Multiple PSAP URIs: The mapping protocol MUST support a method
to return multiple PSAP URIs which cover the same geographic area. to return multiple PSAP URIs which cover the same geographic area.
Motivation: Two different mapping servers may cover the same Motivation: Different contact protocols (e.g., PSTN via tel URIs
geographic area, and therefore have the same set of coverage and IP via SIP URIs) may be routed to different PSAPs. Less
information. likely, two PSAPs may overlap in their coverage region.
Ma8. Single primary URI per contact protocol: Though the mapping Ma8. Single primary URI per contact protocol: Though the mapping
protocol supports multiple URIs being returned, it SHOULD return protocol may be able to include multiple URIs in the response, it
only one primary URI per contact protocol used, so that clients SHOULD return only one primary URI per contact protocol used, so
are not required to select among different targets for the same that clients are not required to select among different targets
contact protocol. for the same contact protocol.
Motivation: There may be two or more URIs returned when multiple Motivation: There may be two or more URIs returned when multiple
contact protocols are available (e.g., SIP and SMS). The client contact protocols are available (e.g., SIP and SMS). The client
may select among multiple contact protocols based on its may select among multiple contact protocols based on its
capabilities, preference settings, or availability. capabilities, preference settings, or availability.
Ma9. URI alternate contact: In addition to returning a primary Ma9. URI alternate contact: In addition to returning a primary
contact, the mapping protocol MUST support the return of a PSAP contact, the mapping protocol MUST support the return of a PSAP
URI or contact method explicitly marked as an alternate contact URI or contact method explicitly marked as an alternate contact
for use when a fallback contact is needed. for use when a fallback contact is needed.
Motivation: In response to a mapping request, the mapping server Motivation: There may be multiple ways to provide addresses of
will also return an alternate URI. Implementation details to be backup PSAPs, including the mapping protocol, DNS lookup via NAPTR
described within an operational document. and SRV, or call routing by SIP proxies.
Ma10. Non-preferred URI schemes: The mapping protocol MAY support Ma10. Non-preferred URI schemes: The mapping protocol MAY support
the return of a less preferred URI scheme, (e.g., TEL URI). the return of a less preferred URI scheme, such as a tel URI.
Motivation: In order to provide incremental support to non-IP Motivation: In order to provide incremental support to non-IP
PSAPs it may be necessary to be able to complete an emergency call PSAPs it may be necessary to be able to complete an emergency call
via the PSTN. via the PSTN.
Ma11. URI properties: The mapping protocol MUST support the ability Ma11. URI properties: The mapping protocol MUST support the ability
to provide ancillary information about a contact that allows the to provide ancillary information about a contact that allows the
mapping client to determine relevant properties of the PSAP URI. mapping client to determine relevant properties of the PSAP URI.
Motivation: In some cases, the same geographic area is served by Motivation: In some cases, the same geographic area is served by
several PSAPs, for example, a corporate campus might be served by several PSAPs, for example, a corporate campus might be served by
both a corporate security department and the municipal PSAP. The both a corporate security department and the municipal PSAP. The
mapping protocol should then return URIs for both, with mapping protocol should then return URIs for both, with
information allowing the querying entity to choose one or the information allowing the querying entity to choose one or the
other. This determination could be made by either an ESRP, based other. This determination could be made by either an ESRP, based
on local policy, or by direct user choice, in the case of caller- on local policy, or by direct user choice, in the case of caller-
based methods. based methods.
Ma12. Mapping referral: The mapping protocol MUST support a Ma12. Mapping referral: The mapping protocol MUST support a
mechanism for the mapping client to contact any mapping server and mechanism for the mapping client to contact any mapping server and
be referred to another mapping server that is more qualified to be referred to another mapping server that is more qualified to
answer the query. answer the query.
Motivation: To help avoid the case of relying on incorrect Motivation: Referrals help mitigate the impact of incorrect
configuration data which may cause calls to fail, particularly for configuration that directs a client to the wrong initial mapping
caller-based mapping queries. server.
Ma13. Split responsibility: The mapping protocol MUST support the Ma13. Split responsibility: The mapping protocol MUST support the
division of data subset handling between multiple mapping servers division of data subset handling between multiple mapping servers
within a single level of a civic location hierarchy. within a single level of a civic location hierarchy.
Motivation: For example, two mapping servers for the same city or Motivation: For example, two mapping servers for the same city or
county may handle different streets within that city or county. county may handle different streets within that city or county.
Ma14. URL for error reporting: The mapping protocol MUST support the 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 ability to return a URL that can be used to report a suspected or
known error within the mapping database. known error within the mapping database.
Motivation: If an error is returned, for example, there needs to Motivation: If an error is returned, for example, there needs to
be a URL which points to a resource which can explain or be a URL which points to a resource which can explain or
potentially help resolve the error. potentially help resolve the error.
Ma15. Resiliance to failure: The mapping protocol MUST support a Ma15. Resiliance to failure: The mapping protocol MUST support a
mechanism which enables fail over to different (replica) mapping mechanism which enables the client to fail over to different
server in order to obtain and return a successful mapping to the (replica) mapping server.
mapping client.
Motivation: It is important that the failure of a single mapping Motivation: The failure of a mapping server should not preclude
server does not preclude the mapping client's ability to receive the mapping client from receiving an answer to its query.
mapping from a different mapping server.
Ma16. Traceable resolution: The mapping protocol SHOULD support the Ma16. Traceable resolution: The mapping protocol SHOULD support the
ability of the mapping client to be able to determine the entity ability of the mapping client to be able to determine the entity
or entities that provided the emergency address resolution or entities that provided the emergency address resolution
information. information.
Motivation: It is important for public safety reasons, that there Motivation: To improve reliability and performance, it is
is a method to provide operational traceability in case of errors. important to be able to trace which servers contributed to the
resolution of a query.
Ma17. Minimal additional delay: Mapping protocol execution SHOULD Ma17. Minimal additional delay: Mapping protocol execution SHOULD
minimize the amount of delay within the overall call-setup time. minimize the amount of delay within the overall call-setup time.
Motivation: Since outbound proxies will likely be asked to resolve Motivation: Since outbound proxies will likely be asked to
the same geographic coordinates repeatedly, a suitable time- resolve the same geographic coordinates repeatedly, a suitable
limited caching mechanism should be supported. time-limited caching mechanism should be supported.
8. Security Considerations Ma18. 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.
Ma19. Freshness 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.
9. Security Considerations
Threats and security requirements are discussed in a separate Threats and security requirements are discussed in a separate
document, see I-D.ietf-ecrit-security-threats [7] . document [11].
9. IANA Considerations 10. IANA Considerations
This document does not require actions by the IANA. This document does not require actions by the IANA.
10. Contributors 11. Contributors
The information contained in this document is a result of a several The information contained in this document is a result of a several
original joint contributions of text, which was then discussed and original joint contributions of text, which was then discussed and
refined by those and many others within the working group. These refined by those and many others within the working group. These
contributors to the early text include, Nadine Abbott, Hideki Arai, contributors to the early text include, Nadine Abbott, Hideki Arai,
Martin Dawson, Motoharu Kawanishi, Brian Rosen, Richard Stastny, Martin Dawson, Motoharu Kawanishi, Brian Rosen, Richard Stastny,
Martin Thomson, James Winterbottom. Martin Thomson, James Winterbottom.
The contributors can be reached at: The contributors can be reached at:
skipping to change at page 28, line 5 skipping to change at page 30, line 5
Motoharu Kawanishi kawanishi381@oki.com Motoharu Kawanishi kawanishi381@oki.com
Brian Rosen br@brianrosen.net Brian Rosen br@brianrosen.net
Richard Stastny Richard.Stastny@oefeg.at Richard Stastny Richard.Stastny@oefeg.at
Martin Thomson Martin.Thomson@andrew.com Martin Thomson Martin.Thomson@andrew.com
James Winterbottom James.Winterbottom@andrew.com James Winterbottom James.Winterbottom@andrew.com
11. Acknowledgments 12. Acknowledgments
In addition to thanking those listed above, we would like to also In addition to thanking those listed above, we would like to also
thank Guy Caron, Barry Dingle, Keith Drage, Tim Dunn, Patrik thank Guy Caron, Barry Dingle, Keith Drage, Tim Dunn, Patrik
Faeltstroem, Clive D.W. Feather, Raymond Forbes, Randall Gellens, Faltstrom, Clive D.W. Feather, Raymond Forbes, Randall Gellens,
Michael Haberler, Michael Hammer, Ted Hardie, Gunnar Hellstrom, Michael Haberler, Michael Hammer, Ted Hardie, Gunnar Hellstrom,
Cullen Jennings, Marc Linsner, Rohan Mahy, Patti McCalmont, Don Cullen Jennings, Marc Linsner, Rohan Mahy, Patti McCalmont, Don
Mitchell, John Morris, Andrew Newton, Steve Norreys, Jon Peterson, Mitchell, John Morris, Andrew Newton, Steve Norreys, Jon Peterson,
James Polk, Benny Rodrig, John Rosenberg, Jonathan Rosenberg, John James Polk, Benny Rodrig, John Rosenberg, Jonathan Rosenberg, John
Schnizlein, Shida Schubert, James Seng, Byron Smith, Tom Taylor, Schnizlein, Shida Schubert, James Seng, Byron Smith, Barbara Stark,
Barbara Stark, Hannes Tschofenig, and Nate Wilcox, for their Tom Taylor, Hannes Tschofenig, and Nate Wilcox for their helpful
invaluable input. input.
12. References 13. References
12.1. Normative References 13.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
12.2. Informative References 13.2 Informative References
[2] Charlton, N., Gasson, M., Gybels, G., Spanner, M., and A. van [2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[3] Charlton, N., Gasson, M., Gybels, G., Spanner, M., and A. van
Wijk, "User Requirements for the Session Initiation Protocol Wijk, "User Requirements for the Session Initiation Protocol
(SIP) in Support of Deaf, Hard of Hearing and Speech-impaired (SIP) in Support of Deaf, Hard of Hearing and Speech-impaired
Individuals", RFC 3351, August 2002. Individuals", RFC 3351, August 2002.
[3] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. [4] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004. Polk, "Geopriv Requirements", RFC 3693, February 2004.
[4] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host [5] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location Configuration Protocol Option for Coordinate-based Location
Configuration Information", RFC 3825, July 2004. Configuration Information", RFC 3825, July 2004.
[5] Hellstrom, G. and P. Jones, "RTP Payload for Text [6] Peterson, J., "Common Profile for Instant Messaging (CPIM)",
RFC 3860, August 2004.
[7] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004.
[8] Hellstrom, G. and P. Jones, "RTP Payload for Text
Conversation", RFC 4103, June 2005. Conversation", RFC 4103, June 2005.
[6] Peterson, J., "A Presence-based GEOPRIV Location Object [9] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005. Format", RFC 4119, December 2005.
[7] Taylor, T., "Security Threats and Requirements for Emergency [10] Schulzrinne, H. and J. Polk, "Communications Resource Priority
Call Marking and Mapping", draft-ietf-ecrit-security-threats-01 for the Session Initiation Protocol (SIP)", RFC 4412,
(work in progress), April 2006. February 2006.
[8] Schulzrinne, H., "A Uniform Resource Name (URN) for Services", [11] Taylor, T., "Security Threats and Requirements for Emergency
Call Marking and Mapping", draft-ietf-ecrit-security-threats-03
(work in progress), July 2006.
[12] Schulzrinne, H., "A Uniform Resource Name (URN) for Services",
draft-ietf-ecrit-service-urn-03 (work in progress), May 2006. draft-ietf-ecrit-service-urn-03 (work in progress), May 2006.
[9] Hardie, T., "LoST: A Location-to-Service Translation Protocol", [13] Hardie, T., "LoST: A Location-to-Service Translation Protocol",
draft-hardie-ecrit-lost-00 (work in progress), March 2006. draft-hardie-ecrit-lost-00 (work in progress), March 2006.
[10] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4 [14] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4
and DHCPv6) Option for Civic Addresses Configuration and DHCPv6) Option for Civic Addresses Configuration
Information", draft-ietf-geopriv-dhcp-civil-09 (work in Information", draft-ietf-geopriv-dhcp-civil-09 (work in
progress), January 2006. progress), January 2006.
[11] Wijk, A., "Framework for real-time text over IP using SIP", [15] Wijk, A. and G. Gybels, "Framework for real-time text over IP
draft-ietf-sipping-toip-04 (work in progress), March 2006. using the Session Initiation Protocol (SIP)",
draft-ietf-sipping-toip-05 (work in progress), June 2006.
[16] Institute of Electrical and Electronics Engineers, "Station and
Media Access Control Connectivity Discovery", IEEE Standard
802.1 AB, April 2005.
Authors' Addresses Authors' Addresses
Henning Schulzrinne Henning Schulzrinne
Columbia University Columbia University
Department of Computer Science Department of Computer Science
450 Computer Science Building 450 Computer Science Building
New York, NY 10027 New York, NY 10027
US US
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