Network Working Group                                     H. Schulzrinne
Request for Comments: 5012                                   Columbia U.
Category: Informational                                 R. Marshall, Ed.
                                                            January 2008
Network Working Group                                     H. Schulzrinne
Request for Comments: 5012                                   Columbia U.
Category: Informational                                 R. Marshall, Ed.
                                                            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.




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
   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
1. Introduction
1. 介绍

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.

映射协议的主要目的是基于位置信息[RFC4119]和服务标识符来产生从诸如SIP或SIPS URI的优选URI方案集合中提取的PSAP URI,以便促进紧急呼叫的IP端到端完成。

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.


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.

由于一些psap可能不立即支持IP,或者因为一些用户设备(UE)可能最初不支持紧急服务标识符,因此可能还需要支持使用较少优选URI方案的紧急服务标识符,例如tel URI,以便通过PSTN完成紧急呼叫。

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
2. 需求术语

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.

本文件中的关键词“必须”、“不得”、“要求”、“应”、“不得”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[RFC2119]中的描述进行解释,重要的限定条件是,除非另有说明,否则这些术语适用于映射协议的设计,不是它的实现或应用。

3. Terminology
3. 术语
3.1. Emergency Services
3.1. 紧急服务

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
3.2. 服务提供者

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,


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".

语音服务提供商(VSP):一种特定类型的应用程序服务提供商,提供基于IP的语音相关服务,如呼叫路由、SIP URI或PSTN终端。在本文件中,除非另有说明,否则对“语音服务提供商”或“VSP”的任何引用可与“应用程序/语音服务提供商”或“ASP/VSP”互换使用。

3.3. Actors
3.3. 演员

(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.


3.4. Call Routing Entities
3.4. 呼叫路由实体

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.

紧急服务路由代理(ESRP):ESRP是一个紧急呼叫路由支持实体,它调用location to PSAP URI映射函数,以返回适当的PSAP URI或其他ESRP的URI。客户端映射请求也可以由许多实体执行,包括实例化SIP代理角色和SIP用户代理客户端角色的实体。

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.

公共安全应答点(PSAP):公共安全应答点是公共当局负责接收紧急呼叫的设施。(欧洲电信标准协会(ETSI)(ETSI SR 002 180)和英国国家紧急号码协会(NENA)均使用该术语。在英国,PSAP称为运营商援助中心;在新西兰,有通讯中心。在本文档中,除非另有说明,否则假定PSAP支持通过IP接收紧急呼叫,使用适当的应用层协议,如SIP用于呼叫信令,RTP用于媒体。

3.5. Location
3.5. 地方

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


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
3.6. 标识符、号码和拨号字符串

(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.

(紧急)服务号码:(紧急)服务号码是用于到达(紧急)服务的一串数字。紧急服务号码通常被称为紧急号码。它是通常在直接连接到PSTN的设备上拨打的号码,也是国家或地区编号机构为紧急呼叫保留的号码。它只包含数字0到9、#和*。服务号码可能取决于呼叫者的位置。例如,美国的一般紧急服务号码是911,毒物控制服务号码是1800222222。在大多数情况下,服务号码和拨号串是相同的;在某些专用电话网络中,它们可能有所不同。服务编号可以与上下文标识符一起包含在tel URL[RFC3966]中。在北美编号计划中,一些服务编号为三位数N11或服务代码,但并非所有紧急编号都有三位数。使用PBX时,呼叫者可能必须拨打与服务号码不同的服务拨号字符串(如下)。

(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].


(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
3.7. 映射

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.

映射:映射是将一个位置解析为一个或多个PSAP URI的过程,这些URI直接标识PSAP,或指向了解PSAP并被指定为负责服务该位置的中介。

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.

映射服务器:映射服务器保存关于位置到PSAP URI映射的信息。

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
4. 基本行动者

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.


      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             |
      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


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.

1. 位置信息可能对终端主机本身可用。

2. Location information might, however, also be obtained from the Internet Access Provider.

2. 但是,也可以从互联网接入提供商处获得位置信息。

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.

3. 紧急呼叫者可能需要咨询映射服务,以确定适合紧急呼叫者物理位置的PSAP(或其他相关信息),可能需要考虑其他属性,例如紧急呼叫者提供的适当语言支持。

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.

4. 紧急呼叫方可以通过作为紧急呼叫路由支持实体的基础结构元素(如SIP中的紧急服务路由代理(ESRP))获得紧急呼叫路由的帮助。

5. Location information is used by emergency call routing support entities for subsequent mapping requests.

5. 位置信息由紧急呼叫路由支持实体用于后续映射请求。

6. Emergency call routing support entities might need to consult a mapping service to determine where to route the emergency call.

6. 紧急呼叫路由支持实体可能需要咨询映射服务,以确定将紧急呼叫路由到何处。

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.

7. 对于基于基础设施的紧急呼叫路由(与基于UE的紧急呼叫路由相反),紧急呼叫路由支持实体需要将呼叫转发到PSAP。

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.

8. 紧急呼叫方可以直接与PSAP交互,其中UE调用映射并发起连接,而不依赖任何中间紧急呼叫路由支持实体。

5. High-Level Requirements
5. 高层次要求

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.


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.

动机:在PSTN中,语音和文本电话(在北美通常称为TTY或文本电话)是唯一普遍支持的媒体。紧急呼叫必须支持多种媒体。此类媒体应包括语音、对话文本(RFC 4103[RFC4103])、即时消息和视频。

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.

Re6。PSAP URI可访问性:映射协议必须支持不存在或不需要注册映射服务的客户端和服务器之间的交互。

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]).

动机:理想情况下,不通过映射协议提供身份信息。在提供身份信息的情况下,可以采用未链接的笔名形式(RFC 3693[RFC3693])。

6. Identifying the Caller's Location
6. 识别呼叫者的位置

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 inserted:呼叫者的用户代理将位置信息插入到呼叫信令消息中。

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.


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.

Lo5。有关用于映射的位置数据的信息:映射协议必须支持提供有关用于检索PSAP URI的位置数据的解析的辅助信息。

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.


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.

动机:了解存储在用于位置验证的数据库中的数据源非常有用,无论是用于城市还是地理位置匹配。在美国,数据来源可能包括美国邮政局、Master Street Address Guide(MSAG)或商业地图数据提供商。

7. Emergency Service Identifier
7. 紧急服务标识符

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.

紧急服务标识符是协议常量,允许协议实体(如SIP代理服务器)区分紧急呼叫和非紧急呼叫,并识别所需的特定紧急服务。紧急服务标识符是服务标识符的一个子类,通常用于标识呼叫者可访问的服务。服务标识符的一个示例是服务URN[RFC5031],但是其他标识符,例如tel uri[RFC3966],也可以在过渡期间充当此角色。

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.


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.


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.

Id8。Return fallback service identifier:如果映射协议用另一个服务替换请求的服务,则映射协议必须能够报告映射的实际服务。

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.

动机:如果用户请求的服务在该位置不可用,可以将映射服务器配置为自动查找另一个服务的PSAP。例如,如果没有海上救援服务,映射协议可能会返回一般紧急情况下的PSAP URL,并在响应中包含“urn:service.sos”标识符,以提醒查询者该事实。

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
8. 映射协议

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


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.


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.

Ma7。多个PSAP URI:映射协议必须支持返回多个PSAP URI的方法,这些PSAP URI覆盖相同的地理区域。

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.

动机:不同的联系协议(例如,通过电话URI的PSTN和通过SIP URI的IP)可以路由到不同的PSAP。不太可能,两个PSAP可能在其覆盖区域重叠。

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.

Ma9。非首选URI方案:映射协议可能支持返回不太首选的URI方案,例如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.

动机:为了向非IP PSAP提供增量支持,可能需要能够通过PSTN完成紧急呼叫。

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.

Ma10。URI属性:映射协议必须支持提供有关联系人的辅助信息的能力,该信息允许映射客户端确定PSAP URI的相关属性。

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.

Ma12。划分责任:映射协议必须支持在civic location层次结构的单个级别内的多个映射服务器之间划分数据子集处理。

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.


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
9. 安全考虑

Threats and security requirements are discussed in a separate document [RFC5069].


10. Contributors
10. 贡献者

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


Nadine Abbott


Hideki Arai


Martin Dawson


Motoharu Kawanishi


Brian Rosen


Richard Stastny


Martin Thomson


James Winterbottom


11. Acknowledgments
11. 致谢

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. 工具书类
12.1. Normative References
12.1. 规范性引用文件

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

[RFC2119]Bradner,S.,“RFC中用于表示需求水平的关键词”,BCP 14,RFC 2119,1997年3月。

12.2. Informative References
12.2. 资料性引用

[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.

[RFC3261]Rosenberg,J.,Schulzrinne,H.,Camarillo,G.,Johnston,A.,Peterson,J.,Sparks,R.,Handley,M.,和E.Schooler,“SIP:会话启动协议”,RFC 3261,2002年6月。

[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.

[RFC3351]N.查尔顿、M.加斯森、G.吉贝尔斯、M.斯潘纳和A.范·威克,“支持聋人、听力障碍者和言语障碍者的会话启动协议(SIP)的用户需求”,RFC 3351,2002年8月。

[RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004.

[RFC3693]Cuellar,J.,Morris,J.,Mulligan,D.,Peterson,J.,和J.Polk,“地质驱动要求”,RFC 3693,2004年2月。

[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.

[RFC3966]Schulzrinne,H.,“电话号码的电话URI”,RFC 3966,2004年12月。

[RFC4103] Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation", RFC 4103, June 2005.

[RFC4103]Hellstrom,G.和P.Jones,“文本对话的RTP有效负载”,RFC 4103,2005年6月。

[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object Format", RFC 4119, December 2005.


[RFC4412] Schulzrinne, H. and J. Polk, "Communications Resource Priority for the Session Initiation Protocol (SIP)", RFC 4412, February 2006.

[RFC4412]Schulzrinne,H.和J.Polk,“会话启动协议(SIP)的通信资源优先级”,RFC 4412,2006年2月。

[RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for Emergency and Other Well-Known Services", RFC 5031, January 2008.

[RFC5031]Schulzrinne,H.,“应急和其他知名服务的统一资源名称(URN)”,RFC 5031,2008年1月。

[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.

[RFC5069]Taylor,T.,Ed.,Tschofenig,H.,Schulzrinne,H.,和M.Shanmugam,“紧急呼叫标记和映射的安全威胁和要求”,RFC 5069,2008年1月。

[lost] Hardie, T., "LoST: A Location-to-Service Translation Protocol", Work in Progress, August 2007.

[lost]Hardie,T.,“lost:Location to Service Translation Protocol”,正在进行的工作,2007年8月。

[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
   Phone: +1 212 939 7004

Roger Marshall (editor) TeleCommunication Systems, Inc. 2401 Elliott Avenue 2nd Floor Seattle, WA 98121 US


   Phone: +1 206 792 2424
   Phone: +1 206 792 2424

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.

本文件受BCP 78中包含的权利、许可和限制的约束,除其中规定外,作者保留其所有权利。



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.

IETF对可能声称与本文件所述技术的实施或使用有关的任何知识产权或其他权利的有效性或范围,或此类权利下的任何许可可能或可能不可用的程度,不采取任何立场;它也不表示它已作出任何独立努力来确定任何此类权利。有关RFC文件中权利的程序信息,请参见BCP 78和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


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