GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc5012

Network Working Group H. Schulzrinne Request for Comments: 5012 Columbia U. Category: Informational R. Marshall, Ed.

                                                                   TCS
                                                          January 2008
         Requirements for Emergency Context Resolution with
                       Internet Technologies

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Abstract

 This document defines terminology and 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.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
 2.  Requirements Terminology . . . . . . . . . . . . . . . . . . .  3
 3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.1.  Emergency Services . . . . . . . . . . . . . . . . . . . .  3
   3.2.  Service Providers  . . . . . . . . . . . . . . . . . . . .  3
   3.3.  Actors . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.4.  Call Routing Entities  . . . . . . . . . . . . . . . . . .  5
   3.5.  Location . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.6.  Identifiers, Numbers, and Dial Strings . . . . . . . . . .  6
   3.7.  Mapping  . . . . . . . . . . . . . . . . . . . . . . . . .  7
 4.  Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . .  8
 5.  High-Level Requirements  . . . . . . . . . . . . . . . . . . . 10
 6.  Identifying the Caller's Location  . . . . . . . . . . . . . . 12
 7.  Emergency Service Identifier . . . . . . . . . . . . . . . . . 14
 8.  Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 16
 9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20
 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 20
 11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 21
 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
   12.1. Normative References . . . . . . . . . . . . . . . . . . . 21
   12.2. Informative References . . . . . . . . . . . . . . . . . . 21

Schulzrinne & Marshall Informational [Page 1] RFC 5012 ECRIT Requirements January 2008

1. Introduction

 Users of both voice-centric (telephone-like) and non-voice services,
 such as text communication for hearing-disabled users (see [RFC3351]
 and [toip]), expect 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 Session Initiation Protocol (SIP) [RFC3261]
 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 in
 an IP-capable public safety answering point (PSAP), conveyed entirely
 over an IP network.
 We first define terminology in Section 3.  The document then outlines
 various functional issues that relate to placing an IP-based
 emergency call, including a description of baseline requirements
 (Section 5), identification of the emergency caller's location
 (Section 6), use of a service identifier to declare a call to be an
 emergency call (Section 7), and finally, the mapping function
 required to route the call to the appropriate PSAP (Section 8).
 The primary purpose of the mapping protocol is to produce a PSAP URI
 drawn from a preferred set of URI schemes such as SIP or SIPS URIs,
 based on both location information [RFC4119] 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 emergency number is not known, only the
 location.  The mapping protocol can then return a geographically
 appropriate emergency number based on the input.

Schulzrinne & Marshall Informational [Page 2] RFC 5012 ECRIT Requirements January 2008

 Since some PSAPs may not immediately support IP, or because some user
 equipment (UE) may not initially support emergency service
 identifiers, 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
 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 to help in
 dispatching emergency assistance to the appropriate location.
 This latter use, the display of location information to the PSAP, is
 orthogonal to the mapping protocol, and is outside the scope of this
 document.

2. Requirements Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119],
 with the important qualification that, unless otherwise stated, these
 terms apply to the design of the mapping protocol, not its
 implementation or application.

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
    able to determine the identity or geographic location of the
    caller, except by the call taker asking the caller.
 Enhanced emergency service:  In enhanced emergency service, the PSAP
    call taker can determine the caller's current location.

3.2. Service Providers

 Internet Access Provider (IAP):  An organization that provides
    physical and data link (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,

Schulzrinne & Marshall Informational [Page 3] RFC 5012 ECRIT Requirements January 2008

    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 data link (layer-2)
    connectivity, such as fiber or Ethernet, i.e., it may or may not
    play 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 that provides voice related services based on IP, such as
    call routing, a SIP URI, or PSTN termination.  In this document,
    unless noted otherwise, any reference to "Voice Service Provider"
    or "VSP" may be used interchangeably with "Application/Voice
    Service Provider" or "ASP/VSP".

3.3. Actors

 (Emergency) caller:  The term "caller" or "emergency caller" refers
    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 user equipment.
 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.

Schulzrinne & Marshall Informational [Page 4] RFC 5012 ECRIT Requirements January 2008

3.4. Call Routing Entities

 Emergency Service Routing Proxy (ESRP):  An ESRP is an emergency call
    routing support entity that invokes the location-to-PSAP URI
    mapping function, to return an appropriate PSAP URI, or the URI
    for another ESRP.  Client mapping requests could also be performed
    by a number of entities, including entities that instantiate the
    SIP proxy role and the SIP user agent client role.
 Public Safety Answering Point (PSAP):  A PSAP is a facility where
    emergency calls are received under the responsibility of a public
    authority.  (This terminology is used by both the European
    Telecommunications Standards Institute (ETSI), in ETSI SR 002 180,
    and the National Emergency Number Association (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 PSAPs support the receipt
    of emergency calls over IP, using appropriate application layer
    protocols, such as SIP for call signaling and RTP for media.

3.5. Location

 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 reference system,
    such as jurisdictional region or postal delivery grid.  A street
    address is a common example of a civic location.
 Geographic location:  A reference to a point that is able to be
    located, as described by a set of defined coordinates within a
    geographic coordinate system, such as latitude and longitude
    within the WGS-84 datum.  For example, a 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., United States Postal Address or
    the WGS-84 datum) 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, but rather may only

Schulzrinne & Marshall Informational [Page 5] RFC 5012 ECRIT Requirements January 2008

    ensure that the location falls within some range of known values.
    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.

3.6. Identifiers, Numbers, and Dial Strings

 (Emergency) service number:  The (emergency) service number is a
    string of digits used to reach the (emergency) service.  The
    emergency service number is often just called the emergency
    number.  It is the number typically dialed on devices directly
    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
    [RFC3966], along with a context identifier.  In the North American
    numbering plan, some service numbers are 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.
 (Emergency) service dial string:  The service dial string identifies
    the string of digits that a caller must dial to reach a particular
    (emergency) service.  In devices directly connected to the PSTN,
    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.
 (Emergency) service identifier:  The (emergency) service identifier
    describes the emergency service, independent of the user interface
    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 [RFC5031].

Schulzrinne & Marshall Informational [Page 6] RFC 5012 ECRIT Requirements January 2008

 (Emergency) service URL:  The service URL is a protocol-specific
    (e.g., SIP) or protocol-agnostic (e.g., im: [RFC3860]) identifier
    that contains the address of the PSAP or other emergency service.
    It depends on the specific signaling or data transport protocol
    used to reach the emergency service.
 Service URN:  A service URN is an implementation of a service
    identifier, which can be applied to both emergency and non-
    emergency contexts, e.g., urn:service:sos or
    urn:service:counseling.  Within this document, service URNs are
    referred to as 'emergency service URNs' [RFC5031].
 Home emergency number:  A home emergency number is the emergency
    number valid at the caller's customary home location, e.g., his
    permanent residence.  The home location may or may not coincide
    with the service area of the caller's VSP.
 Home emergency dial string:  A home dial string is the dial string
    valid at the caller's customary home location, e.g., his permanent
    residence.
 Visited emergency number:  A visited emergency number is the
    emergency number valid at the caller's current physical location.
    We distinguish the visited emergency number if the caller is
    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 that directly identify a PSAP, or point to an
    intermediary that 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 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.

Schulzrinne & Marshall Informational [Page 7] RFC 5012 ECRIT Requirements January 2008

 Mapping service:  A network service that uses a distributed mapping
    protocol to perform a mapping between a location and a PSAP, or
    intermediary that knows about the PSAP, and is used to assist in
    routing an emergency call.

4. Basic Actors

 In order to support emergency services covering a large physical
 area, various infrastructure elements are necessary, including
 Internet Access Providers (IAPs), Application/Voice Service Providers
 (ASP/VSPs), Emergency Service Routing Proxy (ESRP) providers, mapping
 service providers, and PSAPs.
 This section outlines which entities will be considered in the
 routing scenarios discussed.
    Location
    Information     +-----------------+
        |(1)        |Internet         |   +-----------+
        v           |Access           |   |           |
   +-----------+    |Provider         |   | Mapping   |
   |           |    | (3)             |   | Service   |
   | Emergency |<---+-----------------+-->|           |
   | Caller    |    | (2)             |   +-----------+
   |           |<---+-------+         |          ^
   +-----------+    |  +----|---------+------+   |
        ^           |  |   Location   |      |   |
        |           |  |   Information<-+    |   |
        |           +--+--------------+ |(5) |   | (6)
        |              |                |    |   |
        |              |    +-----------v+   |   |
        |   (4)        |    |            |   |   |
        +--------------+--->|    ESRP    |<--+---+
        |              |    |            |   |
        |              |    +------------+   |
        |              |          ^          |
        |              |      (7) |          |  +----+--+
        |    (8)       |          +------------>|       |
        +--------------+----------------------->| PSAP  |
                       |                     |  |       |
                       |Application/         |  +----+--+
                       |Voice                |
                       |Service              |
                       |Provider             |
                       +---------------------+
            Figure 1: Framework for Emergency Call Routing

Schulzrinne & Marshall Informational [Page 8] RFC 5012 ECRIT Requirements January 2008

 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.
 Is the Internet Access Provider also the Application/Voice Service
 Provider?  In the Internet today, the roles of Internet access
 provider and application/voice service provider are typically
 provided by different entities.  As a consequence, the Application/
 Voice Service Provider is typically not able to directly determine
 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 Access 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 below:
 1.  Location information might be available to the end host itself.
 2.  Location information might, however, also be obtained from the
     Internet Access Provider.
 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, such as an Emergency Service Routing
     Proxy (ESRP) in SIP.
 5.  Location information is used by emergency call routing support
     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 entity needs to forward the call to the PSAP.

Schulzrinne & Marshall Informational [Page 9] RFC 5012 ECRIT Requirements January 2008

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

5. 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 that 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 the United States or
    municipalities, handle emergency calls within their jurisdiction.
 Re3.  Distributed administration:  Deployment of IP-based emergency
    services MUST NOT depend on a single central administrative
    authority.
    Motivation: The design of the 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.

Schulzrinne & Marshall Informational [Page 10] RFC 5012 ECRIT Requirements January 2008

 Re4.  Multi-mode communication:  IP-based emergency calls MUST
    support multiple communication modes, including, for example,
    audio, video, and text.
    Motivation: Within the 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 [RFC4103]), instant messaging, and video.
 Re5.  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 URI that 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.
 Re6.  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.
 Re7.  Common data structures and formats:  The mapping protocol
    SHOULD support common formats (e.g., PIDF-LO) for location data.
    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 that
    contains civic addresses used by location servers may be used for
    multiple purposes and applications beyond emergency service
    location-to-PSAP URI mapping.
 Re8.  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 [RFC3693]).

Schulzrinne & Marshall Informational [Page 11] RFC 5012 ECRIT Requirements January 2008

6. Identifying the Caller's Location

 Location can either be provided directly (by value), or via a pointer
 (by reference), and represents either a civic location, or a
 geographic location.  An important question is how and when to attach
 location information to the VoIP emergency signaling messages.  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.
 UA-referenced:  The caller's user agent provides a pointer (i.e., a
    location reference), via a permanent or temporary identifier, to
    the location information, which is stored by a location server
    somewhere else and then retrieved by the PSAP, ESRP, or other
    authorized entity.
 Proxy-inserted:  A proxy along the call path inserts the location or
    location reference.
 The following requirements apply:
 Lo1.  Reference datum:  The mapping protocol MUST support the WGS-84
    coordinate reference system and MAY support other coordinate
    reference systems.
    Motivation: Though many different datums exist around the world,
    this document recommends the WGS-84 datum since it is designed to
    describe the whole earth, rather than a single continent or other
    region, and is commonly used to represent Global Positioning
    System coordinates.
 Lo2.  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.
 Lo3.  Alternate community names:  The mapping protocol MUST support
    both the jurisdictional community name and the postal community
    name fields within the PIDF-LO [RFC4119] data.

Schulzrinne & Marshall Informational [Page 12] RFC 5012 ECRIT Requirements January 2008

    Motivation: The mapping protocol must accept queries with either a
    postal or jurisdictional community name field, or both, and
    provide appropriate responses.  If a mapping query contains only
    one community name and the database contains both jurisdictional
    and postal community names, the mapping protocol response SHOULD
    return both community names.
 Lo4.  Validation of civic location:  The mapping protocol MUST be
    able to report the results of validating civic locations (street
    addresses).
    Motivation: Location validation provides an opportunity to help
    ascertain 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 location data.
 Lo5.  Information about location data used for mapping:  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.
 Lo6.  Contact for location problems:  The mapping protocol MUST
    support a mechanism to contact an appropriate authority to resolve
    mapping-related issues for the queried location.  For example, the
    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: Initially, authorities may provide URLs where a human
    user can report problems with an address or location.  In
    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.
 Lo7.  Limits to validation:  Successful validation of a civic
    location MUST NOT be required to place an emergency call.

Schulzrinne & Marshall Informational [Page 13] RFC 5012 ECRIT Requirements January 2008

    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.
 Lo8. 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 queriers may 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 or altitude coordinate had been
    omitted from the mapping request.
 Lo9.  Database type indicator:  The mapping protocol MAY support a
    mechanism that 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, either for civic or
    geographic location matching.  In the United States, sources of
    data could include the United States Postal Service, the Master
    Street Address Guide (MSAG), or commercial map data providers.

7. Emergency Service Identifier

 Emergency service identifiers are protocol constants that allow
 protocol entities, such as SIP proxy servers, to distinguish
 emergency 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 [RFC5031], but other identifiers, such as tel URIs
 [RFC3966], may also serve this role during a transition period.
 Since this document only addresses emergency services, we use the
 terms "emergency service identifier" and "service identifier"
 interchangeably.  Requirements for these identifiers include:
 Id1.  Multiple emergency services:  The mapping protocol MUST be able
    to support different emergency services distinguished by different
    service identifiers.
    Motivation: Some jurisdictions may offer multiple types of
    emergency services that operate independently and can be contacted
    directly; for example, fire, police, and ambulance services.

Schulzrinne & Marshall Informational [Page 14] RFC 5012 ECRIT Requirements January 2008

 Id2.  Extensible emergency service identifiers:  The mapping protocol
    MUST support an extensible list of emergency identifiers, though
    it is not required to provide mappings for every possible service.
    Motivation: Extensibility is required since new emergency 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.
 Id3.  Discovery of emergency number:  The mapping protocol MUST be
    able to return the location-dependent emergency number for the
    location indicated in the query.
    Motivation: Users are trained to dial the appropriate emergency
    number to reach emergency services.  There needs to be a way to
    figure out the emergency number at the current location of the
    caller.
 Id4.  Home emergency number recognition:  User equipment MUST be able
    to translate a home emergency number into an emergency service
    identifier.
    Motivation: The UE could be pre-provisioned with the appropriate
    information in order to perform such a translation or could
    discover the emergency number by querying the mapping protocol
    with its home location.
 Id5.  Emergency number replacement:  There SHOULD be support for
    replacement of the emergency number with the appropriate emergency
    service identifier for each signaling protocol used for an
    emergency call, 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 equipment
    may lack the capability to determine the actual service URL (PSAP
    URI).  The use of local conventions may be required as a
    transition mechanism.  Since relying on recognizing local
    numbering conventions makes it difficult for devices to be used
    outside their home context and for external devices to be
    introduced into a network, protocols should use standardized
    emergency service identifiers.
 Id6.  Emergency service identifier marking:  Signaling protocols MUST
    support emergency service identifiers to mark a call as an
    emergency call.

Schulzrinne & Marshall Informational [Page 15] RFC 5012 ECRIT Requirements January 2008

    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.  This marking
    mechanism is related to, but independent of, marking calls for
    prioritized call handling [RFC4412].
 Id7.  Handling unrecognized emergency service identifiers:  There
    MUST be support for calls that are initiated as emergency calls
    even if the specific emergency service requested is not recognized
    by the ESRP.  Such calls will then be routed to a generic
    emergency service.
    Motivation: Fallback routing allows new emergency services to be
    introduced incrementally, while avoiding non-routable emergency
    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.
 Id8.  Return fallback service identifier:  The mapping protocol MUST
    be able to report back the actual service mapped if the mapping
    protocol substitutes another service for the one requested.
    Motivation: A mapping server may be configured to automatically
    look up the PSAP for another service if the user-requested service
    is not available for that location.  For example, if there is no
    marine rescue service, the mapping protocol might return the PSAP
    URL for general emergencies and include the "urn:service.sos"
    identifier in the response to alert the querier to that fact.
 Id9.  Discovery of visited emergency numbers:  The mapping protocol
    MUST support 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
 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, LoST, is outlined in [lost].
 For caller-based resolution, the caller's user agent invokes the
 mapping protocol to determine the appropriate PSAP based on the

Schulzrinne & Marshall Informational [Page 16] RFC 5012 ECRIT Requirements January 2008

 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 ([RFC4119]).
 Ma3.  Incrementally deployable:  The mapping protocol MUST be
    designed to support its incremental deployment.
    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.
 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 is initiated.
    Motivation: If the mapping query fails at call time, it may be
    advantageous to be able to fall back to the result of an earlier
    mapping query.  This prior knowledge would be obtained by
    performing a mapping query at any time prior to an emergency call.

Schulzrinne & Marshall Informational [Page 17] RFC 5012 ECRIT Requirements January 2008

 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 therefore will
    also 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: Different contact protocols (e.g., PSTN via tel URIs
    and IP via SIP URIs) may be routed to different PSAPs.  Less
    likely, two PSAPs may overlap in their coverage region.
 Ma8.  Single primary URI per contact protocol:  Though the mapping
    protocol may be able to include multiple URIs in the response, 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.
    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.  Non-preferred URI schemes:  The mapping protocol MAY support
    the return of a less-preferred URI scheme, such as a 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.

Schulzrinne & Marshall Informational [Page 18] RFC 5012 ECRIT Requirements January 2008

 Ma10.  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.
 Ma11.  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: Referrals help mitigate the impact of incorrect
    configuration that directs a client to the wrong initial mapping
    server.
 Ma12.  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.
    Motivation: For example, two mapping servers for the same city or
    county may handle different streets within that city or county.
 Ma13.  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 that points to a resource that can explain or potentially
    help resolve the error.
 Ma14.  Resilience to mapping server failure:  The mapping protocol
    MUST support a mechanism that enables the client to fail over to
    different (replica) mapping server.
    Motivation: The failure of a mapping server should not preclude
    the mapping client from receiving an answer to its query.
 Ma15.  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.

Schulzrinne & Marshall Informational [Page 19] RFC 5012 ECRIT Requirements January 2008

    Motivation: To improve reliability and performance, it is
    important to be able to trace which servers contributed to the
    resolution of a query.
 Ma16.  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.
 Ma17.  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 time frame.  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
 document [RFC5069].

10. Contributors

 The information in this document is partially derived from text
 written by the following contributors:
 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

Schulzrinne & Marshall Informational [Page 20] RFC 5012 ECRIT Requirements January 2008

11. Acknowledgments

 In addition to thanking those listed above, we would like to also
 thank Guy Caron, Barry Dingle, Keith Drage, Tim Dunn, Patrik
 Faltstrom, 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, Barbara Stark,
 Richard Stastny, Tom Taylor, Hannes Tschofenig, and Nate Wilcox for
 their helpful input.

12. References

12.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.

12.2. Informative References

 [RFC3261]  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.
 [RFC3351]  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.
 [RFC3693]  Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and
            J. Polk, "Geopriv Requirements", RFC 3693, February 2004.
 [RFC3860]  Peterson, J., "Common Profile for Instant Messaging
            (CPIM)", RFC 3860, August 2004.
 [RFC3966]  Schulzrinne, H., "The tel URI for Telephone Numbers",
            RFC 3966, December 2004.
 [RFC4103]  Hellstrom, G. and P. Jones, "RTP Payload for Text
            Conversation", RFC 4103, June 2005.
 [RFC4119]  Peterson, J., "A Presence-based GEOPRIV Location Object
            Format", RFC 4119, December 2005.

Schulzrinne & Marshall Informational [Page 21] RFC 5012 ECRIT Requirements January 2008

 [RFC4412]  Schulzrinne, H. and J. Polk, "Communications Resource
            Priority for the Session Initiation Protocol (SIP)",
            RFC 4412, February 2006.
 [RFC5031]  Schulzrinne, H., "A Uniform Resource Name (URN) for
            Emergency and Other Well-Known Services", RFC 5031,
            January 2008.
 [RFC5069]  Taylor, T., Ed., Tschofenig, H., Schulzrinne, H., and M.
            Shanmugam, "Security Threats and Requirements for
            Emergency Call Marking and Mapping", RFC 5069,
            January 2008.
 [lost]     Hardie, T., "LoST: A Location-to-Service Translation
            Protocol", Work in Progress, August 2007.
 [toip]     Wijk, A. and G. Gybels, "Framework for real-time text over
            IP using the Session Initiation Protocol  (SIP)", Work
            in Progress, August 2006.

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, Inc.
 2401 Elliott Avenue
 2nd Floor
 Seattle, WA  98121
 US
 Phone: +1 206 792 2424
 EMail: rmarshall@telecomsys.com
 URI:   http://www.telecomsys.com

Schulzrinne & Marshall Informational [Page 22] RFC 5012 ECRIT Requirements January 2008

Full Copyright Statement

 Copyright (C) The IETF Trust (2008).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Schulzrinne & Marshall Informational [Page 23]

/data/webs/external/dokuwiki/data/pages/rfc/rfc5012.txt · Last modified: 2008/01/03 23:59 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki