ecrit B. Rosen Internet-Draft NeuStar Intended status: Standards Track H. Schulzrinne Expires:
January 11,July 31, 2009 Columbia U. J. Polk Cisco Systems A. Newton TranTech/MediaSolv July 10, 2008January 27, 2009 Framework for Emergency Calling using Internet Multimedia draft-ietf-ecrit-framework-06draft-ietf-ecrit-framework-07 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or sheThis Internet-Draft is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed,submitted to IETF in accordancefull conformance with Section 6the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 11,July 31, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract The IETF has several efforts targeted at standardizing various aspects of placing emergency calls. This document describes how all of those component parts are used to support emergency calls from citizens and visitors to authorities. Table of Contents 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 34 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 45 3. Overview of how emergency calls are placed . . . . . . . . . . 78 4. Which devices and services should support emergency calls . . 1011 5. Identifying an emergency call . . . . . . . . . . . . . . . . 1112 6. Location and its role in an emergency call . . . . . . . . . . 1213 6.1. Types of location information . . . . . . . . . . . . . . 1415 6.2. Location determination . . . . . . . . . . . . . . . . . . 1516 6.2.1. User-entered location information . . . . . . . . . . 1617 6.2.2. Access network "wire database" location information . 1617 6.2.3. End-system measured location information . . . . . . . 1718 6.2.4. Network measured location information . . . . . . . . 1819 6.3. Who adds location, endpoint or proxy . . . . . . . . . . . 1819 6.4. Location and references to location . . . . . . . . . . . 1920 6.5. End system location configuration . . . . . . . . . . . . 1920 6.6. When location should be configured . . . . . . . . . . . . 2122 6.7. Conveying location in SIP . . . . . . . . . . . . . . . . 2122 6.8. Location updates . . . . . . . . . . . . . . . . . . . . . 2223 6.9. Multiple locations . . . . . . . . . . . . . . . . . . . . 2324 6.10. Location validation . . . . . . . . . . . . . . . . . . . 2325 6.11. Default location . . . . . . . . . . . . . . . . . . . . . 2425 6.12. Location format conversion . . . . . . . . . . . . . . . . 2426 7. LIS and LoST Discovery . . . . . . . . . . . . . . . . . . . . 2426 8. Routing the call to the PSAP . . . . . . . . . . . . . . . . . 2526 9. Signaling of emergency calls . . . . . . . . . . . . . . . . . 2728 9.1. Use of TLS . . . . . . . . . . . . . . . . . . . . . . . . 2728 9.2. SIP signaling requirements for User Agents . . . . . . . . 2729 9.3. SIP signaling requirements for proxy servers . . . . . . . 2829 10. Call backs . . . . . . . . . . . . . . . . . . . . . . . . . . 2829 11. Mid-call behavior . . . . . . . . . . . . . . . . . . . . . . 2830 12. Call termination . . . . . . . . . . . . . . . . . . . . . . . 2930 13. Disabling of features . . . . . . . . . . . . . . . . . . . . 2930 14. Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2931 15. Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 3031 16. Security Considerations . . . . . . . . . . . . . . . . . . . 3032 17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3032 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 3132 19. Informative References . . . . . . . . . . . . . . . . . . . . 3132 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35 Intellectual Property and Copyright Statements . . . . . . . . . . 3736 1. Terminology This document uses terms from [RFC3261] and [RFC5012]. In addition the following terms are used: Access network: The access network supplies IP packet service to an endpoint. Examples of access networks include digital subscriber lines (DSL), cable modems, IEEE 802.11, WiMaX, enterprise local area networks, or cellular data networks. (Emergency) Call taker: An emergency call taker answers an emergency call at the PSAP. Confidence: Confidence is an estimate indicating how sure the measuring system is that the actual location of the person is within the bounds defined by the uncertainty value, expressed as a percentage. For example, a value of 90% indicates that the actual location is within the uncertainty nine times out of ten. Dispatch Location: The dispatch location is the location used for dispatching responders to the person in need of assistance. The dispatch location must be sufficiently precise to easily locate the callee;caller; it typically needs to be more accurate than the routing location. Emergency services routing proxy (ESRP): An emergency services routing proxy provides routing services for a group of PSAPs. Location configuration: During location configuration, an endpoint learns its physical location. Location conveyance: Location conveyance delivers location information to another element. Location determination: Location determination finds where an endpoint is physically located. For example, the endpoint may contain a GPS receiver used to measure its own location or the location may be determined by a network administrator using a wiremap database. Location Information Server (LIS): A Location Information Server stores location information for retrieval by an authorized entity. Mobile device: A mobile device is a user agent that may change its physical location and possibly its network attachment point during an emergency call. NENA (National Emergency Number Association): The National Emergency Number Association is an organization of professionals to "foster the technological advancement, availability and implementation of a universal emergency telephone number system." It develops emergency calling specifications and procedures. Nomadic device (user): A nomadic user agent is connected to the network temporarily, for relatively short durations, but does not move significantly during the lifetime of a network connection or during the emergency call. Examples include a laptop using an IEEE 802.11 hotspot or a desk IP phone that is moved from one cubicle to another. Physical Location: A physical location describes where a person or device is located in physical space, described by a coordinate system. It is distinguished from the network location, described by a network address. Routing Location: The routing location of a device is used for routing an emergency call and may not be as precise as the Dispatch Location. Stationary device: An stationary device is not mobile and is connected to the network at a fixed, long-term-stable physical location. Examples include home PCs or pay phones. Uncertainty: Uncertainty is an estimate, expressed in a unit of length, indicating the diameter of a circle that contains the device with the probability indicated by the confidence value. 2. Introduction Requesting help in an emergency using a communications device such as a telephone or mobile is an accepted practice in most of the world. As communications devices increasingly utilize the Internet to interconnect and communicate, users will continue to expect to use such devices to request help, regardless of whether or not they communicate using IP. This document describes establishment of a communications session by a user to a "Public Safety Answering Point" (PSAP) that is a call center established by response agencies to accept emergency calls. Such citizen/visitor-to-authority calls can be distinguished from those that are created by responders (authority-to-authority) using public communications infrastructure often involving some kind of priority access as defined in Emergency Telecommunications Service (ETS) in IP Telephony [RFC4190]. They also can be distinguished from emergency warning systems that are authority-to-citizen. Supporting emergency calling requires cooperation by a number of elements, their vendors and service providers. This document discusses how end device and applications create emergency calls, how access networks supply location for some of these devices, how service providers assist the establishment and routing, and how PSAPs receive calls from the Internet. The emergency response community will have to upgrade their facilities to support a wider range of communications services, but cannot be expected to handle wide variation in device and service capability. New devices and services are being made available that could be used to make a request for help that are not traditional telephones, and users are increasingly expecting to use them to place emergency calls. However, many of the technical advantages of Internet multimedia require re-thinking of the traditional emergency calling architecture. This challenge also offers an opportunity to improve the operation of emergency calling technology, while potentially lowering its cost and complexity. It is beyond the scope of this document to enumerate and discuss all the differences between traditional (Public Switched Telephone Network) and IP-based telephony, but calling on the Internet is characterized by: o the interleaving over the same infrastructure of a wider variety of services; o the separation of the access provider from the application provider; o the plethora of different media that can be accommodated; o the potential mobility of all end systems, including endpoints nominally thought of as fixed systems and not just those using radio access technology. For example, consider a wired phone connected to a router using a mobile data network such as EV-DO as an uplink. This document focuses on how devices using the Internet can place emergency calls and how PSAPs can handle Internet multimedia emergency calls natively, rather than describing how circuit-switched PSAPs can handle VoIP calls. In many cases, PSAPs making the transition from circuit-switched interfaces to packet-switched interfaces may be able to use some of the mechanisms described here, in combination with gateways that translate packet-switched calls into legacy interfaces, e.g., to continue to be able to use existing call taker equipment. There are many legacy telephone networks that will persist long after most systems have been upgraded to IP origination and termination of emergency calls. Many of these legacy systems use telephone number based routing. Gateways and conversions between existing systems and newer systems defined by this document will be required. Since existing systems are governed primarily by local government regulations and national standards, the gateway and conversion details will be governed by national standards and thus are out of scope for this document. Existing emergency call systems are organized locally or nationally; there are currently no international standards. However, the Internet crosses national boundaries, and thus international standards for equipment and software are required. To further complicate matters, VoIP endpoints can be connected through tunneling mechanisms such as virtual private networks (VPNs). Tunnels can obscure the identity of the actual access network that knows the location. This significantly complicates emergency calling, because the location of the caller and the first element that routes emergency calls can be on different continents, with different conventions and processes for handling of emergency calls. The IETF has historically refused to create national variants of its standards. Thus, this document attempts to take into account best practices that have evolved for circuit switched PSAPs, but makes no assumptions on particular operating practices currently in use, numbering schemes or organizational structures. This document discusses the use of the Session Initiation Protocol (SIP) [RFC3261] by PSAPs and calling parties. While other inter- domain call signaling protocols may be used for emergency calling, SIP is ubiquitous and possesses the proper support of this use case. Only protocols such as H.323, XMPP/Jingle, ISUP and SIP are suitable for inter-domain communications, ruling out Media Gateway Controller protocols such as MGCP or H.248/Megaco. The latter protocols can be used by the enterprise or carrier placing the call, but any such call would reach the PSAP through a media gateway controller, similar to how inter-domain VoIP calls would be placed. Other signaling protocols may also use protocol translation to communicate with a SIP-enabled PSAP. Existing emergency services rely exclusively on voice and conventional text telephony ("TTY") media streams. However, more choices of media offer additional ways to communicate and evaluate the situation as well as to assist callers and call takers in handling emergency calls. For example, instant messaging and video could improve the ability to communicate and evaluate the situation and to provide appropriate instruction prior to arrival of emergency crews. Thus, the architecture described here supports the creation of sessions of any media type, negotiated between the caller and PSAP using existing SIP protocol mechanisms [RFC3264]. Since this document is a framework document it does not include normative behavior. A companion document, [I-D.ietf-ecrit-phonebcp] describes Best Current Practice for this subject and contains normative language for devices, access and calling network elements. Supporting emergency calling does not require any specialized SIP header fields, request methods, status codes, message bodies, or event packages, but does require that existing mechanisms be used in certain specific ways, as described below. User Agents (UAs) unaware of the recommendations in this draft may be able to place emergency calls, but functionality may be impaired. For example, if the UA does not implement the location mechanisms described, an emergency call may not be routed to the correct PSAP, and if the caller is unable to supply his exact location, dispatch of emergency responders may be delayed. Suggested behavior for both endpoints and servers is provided. From the point of view of the PSAP, three essential elements characterize an emergency call: o The call is routed to the most appropriate PSAP, based primarily on the location of the caller. o The PSAP must be able to automatically obtain the location of the caller with sufficient accuracy to dispatch a responder to help the caller. o The PSAP must be able to re-establish a session to the caller if for any reason the original session is disrupted. 3. Overview of how emergency calls are placed An emergency call can be distinguished (Section 5) from any other call by a unique Service URN [RFC5031] that is placed in the call set-up signaling when a home or visited emergency dial string is detected. Because emergency services are local to specific geographic regions, a caller must obtain his location ( Section 6) prior to making emergency calls. To get this location, either a form of measuring, for example, GPS (Section 6.2.3) is deployed, or the endpoint is configured (Section 6.5) with its location from the access network's Location Information Server (LIS). The location is conveyed (Section 6.7) in the SIP signaling with the call. The call is routed (Section 8) based on location using the LoST protocol [I-D.ietf-ecrit-lost],[RFC5222], which maps a location to a set of PSAP URIs. Each URI resolves to a PSAP or an Emergency Services Routing Proxy (ESRP) that serves as an incoming proxy for a group of PSAPs. The call arrives at the PSAP with the location included in the INVITE request. The following is a quick overview for a typical Ethernet connected telephone using SIP signaling. It illustrates one set of choices for various options presented later in this document. o The phone "boots" and connects to its access network o The phone gets location from the DHCP server in civic [RFC4776] orand/or geo [RFC3825] forms, a HELD server [I-D.ietf-geopriv-http-location-delivery] or the first level switch's LLDP server [LLDP]. o The phone obtains the local emergency dial string(s) from the [I-D.ietf-ecrit-lost][RFC5222] server for its current location. It also receives and caches the PSAP URI obtained from LoST. o Some time later, the user places an emergency call. The phone recognizes an emergency call from the dial strings and uses "urn:service:sos" [RFC5031] to mark an emergency call. o It determinesrefreshes its location via DHCP and updates the PSAP's URI by querying the LoST mapping server with its location. o It puts its location in the SIP INVITE in a Geolocation header [I-D.ietf-sip-location-conveyance] and forwards the call using its normal outbound call processing, which commonly involves an outgoing proxy. o The proxy recognizes the call as an emergency call and routes the call using normal SIP routing mechanisms to the URI specified. o The call routing commonly traverses an incoming proxy server (ESRP) in the emergency services network. That proxy would route the call to the PSAP. o The call is established with the PSAP and mutually agreed upon media streams are created. o The location of the caller is displayed to the call taker. Configuration Servers . . . . . . . . . . . . . . . . . . . . +--------+ +----------+ . . +--------+ | +----------+ | . . | LIS | | | SIP | | . . | |-+ | Registrar|-+ . . +--------+ +----------+ . . ^ ^ . . . | . . . . . . . | . . . . . . | | |[M1][M4] |[M2] | | +--------+ |+--------------+ +--------+ | || | LoST | | ||+-------------------->| Servers|-+ ||| [M3][M5] +--------+ +-------+ ||| | PSAP2 | ||| +-------+ ||| ||| [M6] +-------+ [M7]+------+ [M8]+-------+ Alice ------>| Proxy |---->| ESRP |---->| PSAP1 |-----> Call-Taker +-------+ +------+ +-------+ +-------+ | PSAP3 | +-------+ Figure 1: Emergency Call Component Topology The typical message flow for this example using Alice as the caller: [M1] Alice -> LIS LCP Request(s) (ask for location) LIS -> Alice LCP Reply(s) (replies with location) [M2] Alice -> Registrar SIP REGISTER Registrar -> Alice SIP 200 OK (REGISTER) [M3] Alice -> LoST Server Initial LoST Query (contains location) Lost Server -> Alice Initial LoST Response (contains PSAP-URI and dial string) Some time later, Alice dials or otherwise initiates an emergency call [M4] Alice -> LIS LCP Request (update location) LIS -> ALICE LCP Reply (replies with location) [M5] Alice -> LoST Server Update LoST Query (contains location) Lost Server -> Alice LoST Response (contains PSAP-URI) [M6] Alice to Outgoing Proxy INVITE (service URN, Location and PSAP URI) Outgoing Proxy to ESRP INVITE (service URN, Location and PSAP URI) ESRP to PSAP INVITE (service URN, Location and PSAP URI) 200 OK and ACK propogated back from PSAP to Alice Figure 2 Figure 1 shows emergency call component topology and the text above shows call establishment. These include the following components: o Alice - who makes the emergency call. o Configuration Servers - Servers providing Alice's UA its IP address and other configuration information, perhaps including location by-value or by-reference. In this flow, DHCP is used as an example location configuration protocol (LCP).Configuration servers also may include a SIP registrar for Alice's UA. Most SIP UAs will register, so it will be a common scenario for UAs that make emergency calls to be registered with such a server in the originating calling network. Registration would be required for the PSAP to be able to call back after an emergency call is completed. All the configuration messages are labeled M1 through M3, but could easily require more than 3 messages to complete. o LoST server - Processes the LoST request for Location + Service URN to PSAP-URI Mapping function, either for an initial request from a UA, or an in-call routing by the Proxy server in the originating network, or possibly by an ESRP. o ESRP - The emergency services routing proxy server that is the incoming call proxy in the emergency services domain. The ESRP makes further routing decisions (e.g. based on PSAP state and the location of the caller) to choose the actual PSAP that handles the call. In some jurisdictions, this may involve another LoST query. o PSAP - Call center where emergency calls are destined for. Generally, Alice's UA either has location configured manually, has an integral location measurement mechanism, or it runs a LCP [M1] to obtain location from the access (broadband) network. For most devices, a LCP will be used, for example a DHCPREQUEST message or another location acquisition mechanism. Alice's UA then will most likely register [M2] with a SIP domain. This allows her to be contacted by other SIP entities. Next, her UA will perform an initial LoST query [M3] to learn a URI for use if the LoST query fails during an emergency call, or to use to test the emergency call mechanism. The LoST response may containcontains the dial string for emergency calls appropriate for the location provided. At some time after her device has booted, Alice initiates an emergency call. She may do this by dialing an emergency dial string valid for her current ("local") location, or for her "home" location. The UA recognizes the dial string. The UA attempts to refresh its location [M4], and with that location, to refresh the LoST mapping [M5], in order to get the most accurate information to use for routing the call. If the location request or the LoST request fails, or takes too long, the UA uses values it has cached. The UA creates a SIP INVITE [M6] request that includes the location. [I-D.ietf-sip-location-conveyance] defines a SIP Geolocation header that contains either a location-by-reference URI or a [RFC3986] "cid" URL indicating where in the message body the location-by-value is. The INVITE message is routed to the ESRP [M7], which is the first inbound proxy for the emergency services domain. This message is then routed by the ESRP towards the most appropriate PSAP for Alice's location [M8], as determined by the location and other information. A proxy in the PSAP chooses an available call taker and extends the call to its UA. The 200 OK response to the INVITE request traverses the path in reverse, from call taker UA to PSAP proxy to ESRP to originating network proxy to Alice's UA. The ACK request completes the call set-up and the emergency call is established, allowing the PSAP call- taker to talk to Alice about Alice's emergency. 4. Which devices and services should support emergency calls Current PSAPs support voice calls and real-time text calls placed through PSTN facilities or systems connected to the PSTN. Future PSAPs will however support Internet connectivity and a wider range of media types and provide higher functionality. In general, if a user could reasonably expect to be able to place a call for help with the device, then the device or service should support emergency calling. Certainly, any device or service that looks like and works like a telephone (wired or mobile) should support emergency calling, but increasingly, users have expectations that other devices and services should work. Devices that create media sessions and exchange audio, video and/or text, and have the capability to establish sessions to a wide variety of addresses, and communicate over private IP networks or the Internet, should support emergency calls. 5. Identifying an emergency call Using the PSTN, emergency help can often be summoned by dialing a nationally designated, widely known number, regardless of where the telephone was purchased. The appropriate number is determined by the infrastructure the telephone is connected to. However, this number differs between localities, even though it is often the same for a country or region, as it is in many countries in the European Union. In some countries, there is a single digit sequence that is used for all types of emergencies. In others, there are several sequences that are specific to the type of responder needed, e.g., one for police, another for fire. For end systems, on the other hand, it is desirable to have a universal identifier, independent of location, to allow the automated inclusion of location information and to allow the device and other entities in the call path to perform appropriate processing within the signaling protocol in an emergency call set-up. Since there is no such universal identifier, as part of the overall emergency calling architecture, common emergency call URNs are defined in [RFC5031]. For a single number environment the urn is "urn:service:sos". Users are not expected to "dial" an emergency URN. Rather, appropriate emergency dial strings are translated to corresponding service URNs, carried in the Request-URI of the INVITE request. Such translation is best done by the endpoint, among other reasons, because emergency calls convey location in the signaling, but non emergency calls do not normally do that. If the device recognizes the emergency call, it can include location. Dial string recognition could be performed in a signaling intermediary (proxy server) if for some reason the endpoint does not recognize it. For devices that are mobile or nomadic, an issue arises of whether the home or visited dial strings should be used. Many users would prefer that their home dialing sequences work no matter where they are. However, local laws and regulations may require the visited dialing sequence(s) work. Therefore, the visited dial string must work. Devices must allow at least the configuration of the home country, from which a home dial string can be determined. The mechanism for obtaining the dialing sequences for a given location is provided by LoST [I-D.ietf-ecrit-lost].[RFC5222]. Lost servers must return dial strings for emergency services. If the endpoint does not support the translation of dial strings to telephone numbers, the dialing sequence is represented as a dial string [RFC4967] and the outgoing proxy has to recognize the dial string and translate to the service URN. To determine the local emergency dial string, the proxy needs the location of the endpoint. This may be difficult in situations where the user can roam or be nomadic. Endpoint recognition of emergency dial strings is therefore preferred. If a service provider is unable to guarantee that it can correctly determine local emergency dialstrings, wherever its subscribers may be, then it is required that the endpoint do the recognition. Note: It is undesirable to have a single button emergency call user interface element. These mechanisms tend to result in a very high rate of false or accidental emergency calls. In order to minimize this rate, devices should only initiate emergency calls based on entry of specific emergency call dial strings. Speed dial mechanisms may effectively create single button emergency call invocation and should not be permitted. 6. Location and its role in an emergency call Location is central to the operation of emergency services. It is frequently the case that the caller reporting an emergency is unable to provide a unique, valid location themselves. For this reason, location provided by the endpoint or the access network is needed. For practical reasons, each PSAP generally handles only calls for a certain geographic area, with overload arrangements between PSAPs to handle each others calls. Other calls that reach it by accident must be manually re-routed (transferred) to the most appropriate PSAP, increasing call handling delay and the chance for errors. The area covered by each PSAP differs by jurisdiction, where some countries have only a small number of PSAPs, while others decentralize PSAP responsibilities to the level of counties or municipalities. In most cases, PSAPs cover at least a city or town, but there are some areas where PSAP coverage areas follow old telephone rate center boundaries and may straddle more than one city. Irregular boundaries are common, often for historical reasons. Routing must be done based on actual PSAP service boundaries -- the closest PSAP, or the PSAP that serves the nominal city name provided in the location, may not be the correct PSAP. Accuracy of routing location is a complex subject. Calls must be routed quickly, but accurately, and location determination is often a time/accuracy tradeoff, especially with mobile devices or self measuring mechanisms. It is considered acceptable to base a routing decision on an accuracy equal to the area of one sector of a mobile cell site if no more accurate routing location is available. Routing to the most appropriate PSAP is always calculated on the location of the caller, despite the fact that some emergency calls are placed on behalf of someone else, and the location of the incident is sometimes not the location of the caller. In some cases, there are other factors that enter into the choice of the PSAP that gets the call, such as time of day, caller media requests and language preference, call load, etc. However, location of the caller is the primary input to the routing decision. RoutingLocation is but one of two usesused for locationtwo purposes in anemergency call. The other is forcall handling: routing of the call and dispatch of a responder, which must be very precise.responders. Many mechanisms used to locate a caller have a relatively long "cold start" time. To get a location accurate enough for dispatch may take as much as 30 seconds. This is too long to wait for emergencies. Accordingly, it is common, especially in mobile systems, to use a coarse location, for example, the cell site and sector serving the call, for call routing purposes, and then to update the location when a more precise value is known prior to dispatch. In this document we use "routing location" and "dispatch location" when the distinction matters. Accuracy of dispatch location is sometimes determined by local regulation, and is constrained by available technology. The actual requirement exceeds available technology. It is required that a device making an emergency call close to the "demising" or separation wall between two apartments in a high rise apartment building report location with sufficient accuracy to determine on what side of the wall it is on. This implies perhaps a 3 cm accuracy requirement. As of the date of this memo, typical assisted GPS uncertainty with 95% confidence is 100 m. As technology advances, the accuracy requirements for location will need to be increased. Wired systems using wire tracing mechanisms can provide location to a wall jack in specific room on a floor in a building, and may even specify a cubicle or even smaller resolution. As this discussion illustrates, emergency call systems demand the most stringent location accuracy available. Location usually involves several steps to process and multiple elements are involved. In Internet emergency calling, where the endpoint is located is "determined" using a variety of measurement or wire-tracing methods. Endpoints may be "configured" with their own location by the access network. In some circumstances, a proxy server may insert location into the signaling on behalf of the endpoint. The location is "mapped" to the URI to send the call to, and the location is "conveyed" to the PSAP (and other elements) in the signaling. Likewise, we employ Location Configuration Protocols, Location Mapping Protocols, and Location Conveyance Protocols for these functions. This document provides guidance for generic network configurations with respect to location. It is recognized that unique issues may exist in some network deployments. The IETF will continue to investigate these unique situations and provide further guidance, if warranted, in future documents. 6.1. Types of location information There are several ways location can be specified: Civic: Civic location information describes the location of a person or object by a street address that corresponds to a building or other structure. Civic location may include more fine grained location information such as floor, room and cubicle. Civic information comes in two forms: Jurisdictional refers to a civic location using actual political subdivisions, especially for the community name. Postal refers to a civic location for mail delivery. The name of the post office sometimes does not correspond to the community name and a postal address may contain post office boxes or street addresses that do not correspond to an actual building. Postal addresses are generally unsuitable for emergency call dispatch because the post office conventions (for community name, for example) do not match those known by the responders. The fact that they are unique can sometimes be exploited to provide a mapping between a postal address and a civic address suitable to dispatch a responder to. In IETF location protocols, there is an element (Postal Community Name) that can be included in a location to provide the post office name as well as the actual jurisdictional community name. There is also an element for a postal code. There is no other accommodation for postal addresses in these protocols. Geospatial (geo): Geospatial addresses contain longitude, latitude and altitude information based on an understood datum and earth shape model. While there have been many datums developed over time, most modern systems are using or moving towards the [WGS84] datum. Cell tower/sector: Cell tower/sector is often used for identifying the location of a mobile handset, especially for routing of emergency calls. Cell tower and sectors identify the cell tower and the antenna sector that a mobile device is currently using. Traditionally, the tower location is represented as a point chosen to be within a certain PSAP service boundary who agrees to take calls originating from that tower/sector, and routing decisions are made on that point. Cell/sector information could also be represented as an irregularly shaped polygon of geospatial coordinates reflecting the likely geospatial location of the mobile device. Whatever representation is used must route correctly in the LoST database, where "correct" is determined by local PSAP management. In IETF protocols, both civic and geospatial forms are supported. The civic forms include both postal and jurisdictional fields. A cell tower/sector can be represented as a geo point (geoor civic)polygon or polygon.civic location. Other forms of location representation must be mapped into either a geo or civic for use in emergency calls. For emergency call purposes, conversion of location information from civic to geo or vice versa prior to conveyance is not desirable. The location should be sent in the form it was determined. Conversion between geo and civic requires a database. Where PSAPs need to convert from whatever form they receive to another for responder purposes, they have a suitable database. However, if a conversion is done before the PSAP's, and the database used is not exactly the same one the PSAP uses, the double conversion has a high probability of introducing an error. 6.2. Location determination As noted above, location information can be entered by the user or installer of a device ("manual configuration"), measured by the end system, can be delivered to the end system by some protocol or measured by a third party and inserted into the call signaling. In some cases, an entity may have multiple sources of location information, possibly partially contradictory. This is particularly likely if the location information is determined both by the end system and a third party. Although self measured location (e.g. GPS) is attractive, access network provided location could be much more accurate, and more reliable in some environments such as indoor high rises in dense urban areas. In general, the closer an entity is to the source of location, the more it is in the best position to determine which location is "best" for a particular purpose. In emergency calling, the PSAP is the least likely to be able to appropriately choose which location to use when multiple conflicting locations are presented to it. 6.2.1. User-entered location information Location information can be maintained by the end user or the installer of an endpoint in the endpoint itself, or in a database. Location information provided by end users is almost always less reliable than measured or wire database information, as users may mistype location information or may enter civic address information that does not correspond to a recognized (i.e., valid, see Section Section 6.10) address. Users can forget to change the data when the location of a device changes during or after movement. All that said, there are always a small number of cases where the automated mechanisms used by the access network to determine location fail to accurately reflect the actual location of the endpoint. For example, the user may deploy his own WAN behind an access network, effectively removing an endpoint some distance from the access network's notion of its location. There must be some mechanism provided to provision a location for an endpoint by the user or by the access network on behalf of a user. The use of the mechanism introduces the possibility of users falsely declaring themselves to be somewhere they are not. As an aside, normally, if an emergency caller insists that he is at a location different from what any automatic location determination system reports he is, responders will always be sent to the user's self-declared location. However, this is a matter of local policy and is outside the scope of this document. 6.2.2. Access network "wire database" location information Location information can be maintained by the access network, relating some form of identifier for the end subscriber or device to a location database ("wire database"). In enterprise LANs, wiremap databases map Ethernet switch ports to building locations. In DSL installations, the local telephone carrier maintains a mapping of wire-pairs to subscriber addresses. Accuracy of location historically has been to a street address level. However, this is not sufficient for larger structures. The PIDF-LO [RFC4119] with a recent extension [RFC5139] permits interior building/floor/room and even finer specification of location within a street address. When possible, interior location should be supported. The threshold for when interior location is needed is approximately 650 m2. This value is derived from fire brigade recommendations of spacing of alarm pull stations. However, interior space layout, construction materials and other factors should be considered. The ultimate goal is to be able to find the person in need quickly if responders arrive at the location provided. Even for IEEE 802.11 wireless access points, wire databases may provide sufficient location resolution. The location of the access point as determined by the wiremap may be supplied as the location for each of the clients of the access point. However, this may not be true for larger-scale systems such as IEEE 802.16 (WiMAX) and IEEE 802.22 that typically have larger cells than those of IEEE 802.11. The civic location of an IEEE 802.16 base station may be of little use to emergency personnel, since the endpoint could be several kilometers away from the base station. Wire databases are likely to be the most promising solution for residential users where a service provider knows the customer's service address. The service provider can then perform address validation (see Section 6.10), similar to the current system in some jurisdictions. 6.2.3. End-system measured location information Global Positioning System (GPS) and similar satellite based (e.g., Galileo) receivers may be embedded directly in the end device. GPS produces relatively high precision location fixes in open-sky conditions, but the technology still faces several challenges in terms of performance (time-to-fix and time-to-first-fix), as well as obtaining successful location fixes within shielded structures, or underground. It also requires all devices to be equipped with the appropriate GPS capability. GPS-derived locations are currently accurate to tens of meters. Many mobile devices require using some kind of "assist", that may be operated by the access network (A-GPS) or by a government (WAAS). GPS systems may be always enabled and thus location will always be available accurately immediately (assuming the device can "see" enough satellites). Mobile devices may not be able to sustain the power levels required to keep the measuring system active. In such circumstances, when location is needed, the device has to start up the measurement mechanism. This typically takes tens of seconds, far too long to wait to be able to route an emergency call. For this reason, devices that have end-system measured location mechanisms but need a cold start period lasting more than a couple seconds need another way to get a routing location. Typically this would be a location associated with a radio link (cell site/sector). 6.2.4. Network measured location information The access network may locate end devices. Techniques include: Wireless triangulation: Elements in the network infrastructure triangulate end systems based on signal strength, angle of arrival or time of arrival. Common mechanisms deployed include: * Time Difference Of Arrival - TDOA * Uplink Time Difference Of Arrival - U-TDOA * Angle of Arrival - AOA * RF fingerprinting * Advanced Forward Link Trilateration - AFLT * Enhanced Forward Link Trilateration - EFLT Sometimes multiple mechanisms are combined, for example A-GPS with AFLT Location beacons: A short range wireless beacon, e.g., using Bluetooth or infrared, announces its location to mobile devices in the vicinity. This allows devices to get location from the beacon source's location. 6.3. Who adds location, endpoint or proxy The IETF emergency call architecture prefers endpoints to learn their location and supply it on the call. Where devices do not support location, proxy servers may have to add location to emergency calls. Some calling networks have relationships with all access networks the device may be connected to, and that may allow the proxy to accurately determine location of the endpoint. However, NATs and other middleboxes often make it impossible to determine a reference identifier the access network could use with a LIS to determine the location of the device. Systems designers are discouraged from relying on proxies to add location. The technique may be useful in some limited circumstances as devices are upgraded to meet the requirements of this document, or where relationships between access networks and calling networks are feasible and can be relied upon to get accurate location. Proxy insertion of location complicates dial string recognition. As noted in Section 6, local dial strings depend on the location of the caller. If the device does not know its own location, it cannot use the LoST service to learn the local emergency dial strings. The calling network must provide another way for the device to learn the local dial string, and update it when the user moves to a location where the dial string(s) change, or do the dial string determination itself. 6.4. Location and references to location Location information may be expressed as the actual civic or geospatial value but can be transmitted as by value (wholly contained within the signaling message) or by reference (i.e. as a URI pointing to the value residing on a remote node waiting to be dereferenced). Each form is better suited to some applications than others. When location is transmitted by value, the location information is available to each device; on the other hand, location objects can be large, and only represent a single snapshot of the device's location. Location references are small and can be used to represent a time- varying location, but the added complexity of the dereference step introduces a risk that location will not be available to parties that need it. 6.5. End system location configuration Unless a user agent has access to provisioned or locally measured location information, it must obtain it from the access network. There are several location configuration protocols (LCPs) that can be used for this purpose including DHCP, HELD and LLDP: DHCP can deliver civic [RFC4776] or geospatial [RFC3825] information. User agents need to support both formats. Note that a user agent can use DHCP, via the DHCP REQUEST or INFORM messages, even if it uses other means to acquire its IP address. HELD [I-D.ietf-geopriv-http-location-delivery] can deliver a civic or geo, by value or by reference, as a layer 7 protocol. The query typically uses the IP address of the requestor as an identifier and returns the location value or reference associated with that identifier. HELD is typically carried in HTTP. Link-Layer Discovery Protocol [LLDP] with Media Endpoint Device extensions [LLDP-MED] can be used to deliver location information directly from the Layer 2 network infrastructure, and also supports both civic and geospatial formats identical in format to DHCP methods. Each LCP has limitations in the kinds of networks that can reasonably support it. For this reason, it is not possible to choose a single mandatory-to-deploy LCP. For endpoints with common network connections (such as an Ethernet jack or a WiFi connection) serious incompatibilities would ensue unless every network supported every protocol, or alternatively, every device supported every protocol. For this reason, a mandatory-to-implement list of LCPs is established in [I-D.ietf-ecrit-phonebcp]. Every endpoint that could be used to place emergency calls must implement all of the protocols on the list. Every access network must deploy at least one of them. It is recognized that this is an onerous requirement that would be desirable to eliminate. However, since it is the variability of the networks that prevent a single protocol from being acceptable, it must be the endpoints that implement all of them, and to accommodate a wide range of devices, networks must deploy at least one of them. Often, network operators and device designers believe that they have a simpler environment and some other network specific mechanism can be used to provide location. Unfortunately, it is very rare to actually be able to limit the range of devices that may be connected to a network. For example, existing mobile networks are being used to support routers and LANs behind a wireless data network WAN connection, with Ethernet connected phones connected to that. It is possible that the access network could support a protocol not on the list, and require every handset in that network to use that protocol for emergency calls. However, the Ethernet-connected phone won't be able to acquire location, and the user of the phone is unlikely to be dissuaded from placing an emergency call on that phone. The widespread availability of gateways, routers and other network- broadening devices means that indirectly connected endpoints are possible on nearly every network. Network operators and vendors are cautioned that shortcuts to meeting this requirement are seldom successful. Location for non-mobile devices is normally expected to be acquired at network attachment time and retained by the device. It should be refreshed when the cached value expires. For example, if DHCP is the acquisition protocol, refresh of location may occur when the IP address lease is renewed. At the time of an emergency call, the location should be refreshed, with the retained location used if the location acquisition does not immediately return a value. Mobile devices may determine location at network attachment time and periodically thereafter as a backup in case location determination at the time of call does not work. Mobile device location may be refreshed when a TTL expires or the device moves beyond some boundaries (as provided by [I-D.ietf-ecrit-lost]).[RFC5222]). Normally, mobile devices will acquire its location at call time for use in an emergency call routing. See Section 6.8 for a further discussion on location updates for dispatch location. There are many examples of end devices which are applications running on a more general purpose device, such as a personal computer. In some circumstances, it is not possible for application programs to access the network device at a level necessary to implement the LLDP- MED protocol, and in other cases, obtaining location via DHCP may be impossible. In any case it is desirable for an operating system which could be used for any application which could make emergency calls to have an API which provides the location of the device for use by any application. 6.6. When location should be configured Devices should get routing location immediately after obtaining local network configuration information. The presence of NAT and VPN tunnels (that assign new IP addresses to communications) can obscure identifiers used by LCPs to determine location, especially for HELD. In some cases, such as residential NAT devices, the NAT is placed before the access network demarcation point and thus the IP address seen by the access network is the right identifier for location of the residence. In many enterprise environments, VPN tunnels can obscure the actual IP address. Some VPN mechanisms can be bypassed so that a query to the LCP can be designated to go through the direct IP path, using the correct IP address, and not through the tunnel. In other cases, no bypass is possible. Of course, LCPs that use Layer 2 mechanisms (DHCP Location options and LLDP-MED) are usually immune from such problems because they do not use the IP address as the identifier for the device seeking location. It is desirable that routing location information be periodically refreshed. A LIS supporting a million subscribers each refreshing once per day would need to support a query rate of 1,000,000 / (24 * 60 * 60) = 12 queries per second. It is desirable for routing location information to be requested immediately before placing an emergency call. However, if there is any significant delay in getting more recent location, the call should be placed with the most recent location information the device has. In mobile handsets, routing is often accomplished with the cell site and sector of the tower serving the call, because it can take many seconds to start up the location determination mechanism and obtain an accurate location. There is a tradeoff between the time it takes to get a routing location and the accuracy (technically, confidence and uncertainty) obtained. Routing an emergency call quickly is required. However, if location can be substantially improved by waiting a short time (e.g., for some sort of "quick fix"), it's preferable to wait. Three seconds, the current nominal time for a quick fix, is a very long time to wait for help. Systems designers should attempt to provide accurate routing location in much less time then that. NENA recommends [NENAi3TRD]IP based systems complete calls in two seconds (i.e., last dial press to ring at PSAP). 6.7. Conveying location in SIP When an emergency call is placed, the endpoint should put location in the call signaling. This is referred to as "conveyance" to distinguish it from "configuration". In SIP, the location information is conveyed following the procedures in [I-D.ietf-sip-location-conveyance]. Since the form of the location information obtained by the acquisition protocol may not be the same as the conveyance protocol uses (PIDF-LO [RFC4119]), mapping by the endpoint from the LCP form to PIDF may be required. 6.8. Location updates As discussed above, it may take some time for some measurement mechanisms to get a location accurate enough for dispatch, and a routing location with less accuracy may be provided to get the call established early. The PSAP needs the dispatch location before it sends the call to the responder. This requires an update of the location. In addition, the location of some mobile callers, e.g., in a vehicle or aircraft, can change significantly during the emergency call. While most often this change is not significant, the PSAP must be able to get updated location information while it is processing the call. A PSAP has no way to request an update of a location-by-value. If the UAC gets new location, it must signal the PSAP using a reINVITE or UPDATE method with a new Geolocation header to supply the new location. With the wide variation in determination mechanisms, the PSAP doesn't know when accurate location may be available to it. Therefore, the preferred mechanism is that the LIS notifies the PSAP when accurate location is updated rather than requiring a poll operation from the PSAP to the LIS. The SIP Presence subscription [RFC3856] provides a suitable mechanism. Generally, the PSAP can wait for an accurate location for dispatch. However, there is no fixed limit known in advance; it depends on the nature of the emergency. At some point the PSAP must dispatch. If the LIS is notifying the PSAP with a SUBSCRIBE/NOTIFY mechanism, the PSAP could update the parameters in a filter on the subscription. (immediate response required). When using a HELD dereference, the PSAP must specify the value "emergencyDispatch" for the ResponseTime parameter. The LIS should be aware of the needs of the PSAP as they are local to one another. 6.9. Multiple locations Getting multiple locations all purported to describe the location of the caller is confusing to all, and should be avoided. Handling multiple locations at the point where a PIDF is created is discussed in [I-D.ietf-geopriv-pdif-lo-profile] . Conflicting location information is particularly harmful if different routes (PSAPs) result from LoST queries for the multiple locations. When they occur anyway, the general guidance is that the entity earliest in the chain generally has more knowledge than later elements to make an intelligent decision, especially about which location will be used for routing. It is permissible to send multiple locations towards the PSAP, but the element that chooses the route must select one (and only one) location to use with LoST. Guidelines for dealing with multiple locations are also given in [I-D.ietf-ecrit-lost].[RFC5222]. If a UA gets multiple locations, it must choose the one to use for routing, but it may send all of the locations it has in the signaling. If a proxy is inserting location and has multiple locations, it must choose the one to use to route and send any others it has. The UA or proxy should have the ability to understand how and from whom it learned its location, and should include this information in the location objects that are sent to the PSAP. That labeling provides the call-taker with many pieces of information to make decisions upon, as well as guidance for what to ask the caller and what to tell the responders. The call must indicate the location information that has been used for routing, so that the same location information is used for all call routing decisions. The location conveyance mechanism [I-D.ietf-sip-location-conveyance] contains a parameter for this purpose. 6.10. Location validation It is recommended that locationAn entity may also recieve multiple versions of the same location. For example a database may be validated priorused to a device placing an actual emergency call; some jurisdictions require"geocode" or "reverse geocode", that this be done. Validation in thisis, convert from civic to geo or vice versa. It is very problematic to use derived locations in emergency calls. The PSAP and the responders have very accurate databases which they use to convert, most commonly from a reported geo to a civic suitable for dispatching responders. If one database is used to convert from, say, civic to geo, and another converts from geo to civic, errors will often occur where the databases are slightly different. "Off by one" errors are serious when responders go to the wrong location. Derived locations should be marked with a "derived" method token [RFC4119]. If an entity gets a location which has a measured or other original method, and another with a derived method, it must use the original value for the emergency call. 6.10. Location validation It is recommended that location be validated prior to a device placing an actual emergency call; some jurisdictions require that this be done. Validation in this context means both that there is a mapping from the address to a PSAP and that the PSAP understands how to direct responders to the location. Determining the addresses that are valid can be difficult. There are, for example, many cases of two names for the same street, or two streets with the same name in a city. In some countries, the current system provides validation. For example, in the United States, the Master Street Address Guide (MSAG) records all valid street addresses and is used to ensure that the service addresses in phone billing records correspond to valid emergency service street addresses. Validation is normally a concern for civic addresses, although there could be a concern that a given geo is within at least one PSAP service boundary; that is, a "valid" geo is one where there is a mapping. LoST [I-D.ietf-ecrit-lost][RFC5222] includes a location validation function. Validation is normally performed when a location is entered into a Location Information Server. It should be confirmed periodically, because the mapping database undergoes slow change; new streets are added or removed, community names change, postal codes change, etc. Endpoints may wish to validate locations they receive from the access network, and will need to validate manually entered locations. Proxies that insert location may wish to validate locations they receive from a LIS. When the Test functions (Section 15) are invoked, the location used should be re-validated. When validation fails, the location given must not be used for an emergency call. If validation is complete when location is first loaded into a LIS, any problems can be found and fixed before devices could get the bad location. Failure of validation arises because an error is made in determining the location, although occasionally the LoST database is not up to date or has faulty information. In either case, the problem must be identified and corrected before using the location. 6.11. Default location Occasionally, the access network cannot determine the actual location of the caller. In these cases, it must supply a default location. The default location should be as accurate as the network can determine. For example, in a cable network, a default location for each Cable Modem Termination System (CMTS), with a representative location for all cable modems served by that CMTS could be provided if the network is unable to resolve the subscriber to anything more precise than the CMTS. Default locations must be marked as such so that the PSAP knows that the location is not accurate. 6.12. Location format conversion The endpoint is responsible for mapping any form of location it receives from an LCP into PIDF-LO form if the LCP did not directly return a PIDF. 7. LIS and LoST Discovery Endpoints must be able to discover a LIS (if the HELD protocol is used), and a LoST server. DHCP options are defined for this purpose [I-D.ietf-geopriv-lis-discovery] and [I-D.ietf-ecrit-dhc-lost-discovery][RFC5223] Until such DHCP records are widely available, it may be necessary for the service provider to provision a LoST server address in the device. The endpoint can also do an SRV query within its SIP domain to find a LoST server. In any environment, more than one of these mechanisms may yield a LoST server, and they may be differernt. The recommended priority is DHCP first, provisioned value second, and SRV query in the SIP domain third. 8. Routing the call to the PSAP Emergency calls are routed based on one or more of the following criteria expressed in the call setup request (INVITE): Location: Since each PSAP serves a limited geographic region and transferring existing calls delays the emergency response, calls need to be routed to the most appropriate PSAP. In this architecture, emergency call setup requests contain location information, expressed in civic or geospatial coordinates, that allows such routing. If there is no or imprecise (e.g., cell tower and sector) information at call setup time, an on-going emergency call may also be transferred to another PSAP based on location information that becomes available in mid-call. Type of emergency service: In some jurisdictions, emergency calls for specific emergency services such as fire, police, ambulance or mountain rescue are directed to just those emergency-specific PSAPs. This mechanism is supported by marking emergency calls with the proper service identifier [RFC5031]. Even in single number jurisdictions, not all services are dispatched by PSAPs and may need alternate URNs to route calls to the appropriate call center. Media capabilities of caller: In some cases, emergency call centers for specific caller media preferences, such as typed text or video, are separate from PSAPs serving voice calls. ESRPs are expected to be able to provide routing based on media. Also, even if media capability does not affect the selection of the PSAP, there may be call takers within the PSAP that are specifically trained, e.g., in interactive text or sign language communications, where routing within the PSAP based on the media offer would be provided. Routing for calls by location and by service is the primary function LoST [I-D.ietf-ecrit-lost][RFC5222] provides. LoST accepts a query with location (by-value)(by- value) in either civic or geospatial form, plus a service identifier, and returns a URI (or set of URIs) to route the call to. Normal SIP [RFC3261] routing functions are used to resolve the URI to a next hop destination. The endpoint can complete the LoST mapping from its location at boot time, and periodically thereafter. It should attempt to obtain a "fresh" location, and from that a current mapping when it places an emergency call. If accessing either its location acquisition or mapping functions fail, it should use its cached value. The call would follow its normal outbound call processing. Determining when the device leaves the area provided by the LoST service can tax small mobile devices. For this reason, the LoST server should return a simple (small number of points) polygon for geo reported location. This can be an enclosing subset of the area when the reported point is not near an edge or a smaller edge section when the reported location is near an edge. Civic location is uncommon for mobile devices, but reporting that the same mapping is good within a community name, or even a street, may be very helpful for WiFi connected devices that roam and obtain civic location from the AP they are connected to. Networks that support devices that do not implement LoST mapping themselves may need the outbound proxy do the mapping. If the endpoint recognized the call was an emergency call, provided the correct service URN and/or included location on the call in a Geolocation header, a proxy server could easily accomplish the mapping. However, if the endpoint did not recognize the call was an emergency call, and thus did not include location, the proxy's task is more difficult. It is often difficult for the calling network to accurately determine the endpoint's location by itself. The endpoint may have its location, but would not normally include it on the call signaling unless it knew it was an emergency call. There is no mechanism provided in [I-D.ietf-sip-location-conveyance] to allow a proxy to require the endpoint supply location, because that would open the endpoint to an attack by any proxy on the path to get it to reveal location. The proxy can attempt to redirect a call to the service URN which, if the device recognizes the significance, would include location in the redirected call from the device. All networks should detect emergency calls and supply default location and/or routing if it is not already performed. Often, the SIP routing of an emergency call will first route to an incoming call proxy in the domain operated by the emergency service. That proxy is called an "Emergency Services Routing Proxy" (ESRP). The ESRP, which is a normal SIP proxy server, may use a variety of PSAP state information, the location of the caller, and other criteria to onward route the call to the PSAP. In order for the ESRP to route on media choice, the initial INVITE request has to supply an SDP offer. 9. Signaling of emergency calls 9.1. Use of TLS As discussed above, location is carried in all emergency calls in the call signaling. Since emergency calls carry privacy-sensitive information, they are subject to the requirements for geospatial protocols [RFC3693]. In particular, signaling information should be carried in TLS, i.e., in 'sips' mode with a ciphersuite which includes strong encryption (e.g., AES). There are exceptions in [RFC3693] for emergency calls. For example, local policy may dictate that location is sent with an emergency call even if the user's policy would otherwise prohibit that. Never the less, protection from eavesdropping of location by encryption should be provided. It is unacceptable to have an emergency call fail to complete because a TLS connection was not created for any reason. Thus, the call should be attempted with TLS, but if the TLS session establishment fails, the call should be automatically retried without TLS. [I-D.ietf-sip-sips] recommends that to achieve this effect the target request a sip URI, but use TLS on the outbound connection. An element that receives a request over a TLS connection should attempt to create a TLS connection to the next hop. In many cases, persistent TLS connections can be maintained between elements to minimize the time needed to establish them [I-D.ietf-sip-outbound]. In other circumstances, use of session resumption [RFC5077] is recommended. IPSEC [RFC4301] is an acceptable alternative to TLS when used with an equivalent crypto suite. Location may be used for routing by multiple proxy servers on the path. Confidentiality mechanisms such as S/MIME encryption of SIP signaling [RFC3261] cannot be used because they obscure location. Only hop-by-hop mechanisms such as TLS should be used. Many SIP devices do not support TLS. Implementing location conveyance in SIP mandates inclusion of TLS support. 9.2. SIP signaling requirements for User Agents SIP UAs that do local dial string interpretation, location, and emergency call route will create SIP INVITE messages with the Service URN in the Request URI,URI and To header, the LoST-determined URI for the PSAP in a Route header, and the location in a Geolocation header. The INVITE request must also have appropriate call back identifiers. To enable media sensitive routing, the call should include an SDP offer. 9.3. SIP signaling requirements for proxy servers SIP proxy servers in the path of an emergency call must be able to assist UAs that are unable to provide any of the location based routing steps and recognition of dial strings. They are also expected to provide identity information for the caller. 10. Call backs The call-taker must be able to reach the emergency caller if the original call is disconnected. In traditional emergency calls, wireline and wireless emergency calls include a callback identifier for this purpose. In SIP systems, the caller must include a Contact header field indicating its device URI, if globally routable, or possibly a GRUU [I-D.ietf-sip-gruu] if calls need to be routed via a proxy. This identifier would be used to initiate call-backs immediately by the call-taker if, for example, the call is prematurely dropped. This is a change from [RFC3261] where the Contact: header is optional. In addition, a call-back identifier must be included either as the URI in the From header field [RFC3261] verified by SIP Identity [RFC4474] or as a network asserted URI [RFC3325]. This identifier would be used to initiate a call-back at a later time and may reach the caller, not necessarily on the same device (and at the same location) as the original emergency call as per normal SIP rules. 11. Mid-call behavior PSAPs often include dispatchers, responders or specialists on a call. Some responder's dispatchers are not located in the primary PSAP. The call may have to be transferred to another PSAP. Most often this will be an attended transfer, or a bridged transfer. Therefore a PSAP may need to REFER [RFC3515] a call to a bridge for conferencing. Relay services for communication with people with disabilities may be included in the call in this way. The UA should also be prepared to have the call transferred (usually attended, but possibly blind) as per [I-D.ietf-sipping-service-examples]. SIP Caller Preferences [RFC3841] can be used to signal how the PSAP should handle the call. For example, a language preference expressed in an Accept-Language header may be used as a hint to cause the PSAP to route the call to a call taker who speaks the requested language. SIP Caller Preferences may also be used to indicate a need to invoke a relay service for communication with people with disabilities in the call. 12. Call termination It is undesirable for the caller to terminate an emergency call. PSAP terminates a call using the normal SIP call termination procedures. 13. Disabling of features Certain features that can be invoked while a normal call is active are not permitted when the call is an emergency call. Services such as call waiting, call transfer, three way call and flash Hold should be disabled. Certain features such as call forwarding can interfere with calls from a PSAP and should be disabled. A UA can determine a PSAP call back by examining the domain of incoming calls after placing an emergency call and comparing that to the domain of the answering PSAP from the emergency call. A time limit after an emergency call should be established during which any call from the same domain and directed to the supplied Contact: or AoR should be accepted as a call-back from the PSAP. 14. Media PSAPs should always accept RTP media streams [RFC3550]. Traditionally, voice has been the only media stream accepted by PSAPs. In some countries, text, in the form of Baudot codes or similar tone encoded signaling within a voiceband is accepted ("TTY") for persons who have hearing disabilities. With the Internet comes a wider array of potential media that a PSAP should accept. Using SIP signaling includes the capability to negotiate media. Normal SIP offer/answer [RFC3264] negotiations should be used to agree on the media streams to be used. PSAPs should accept real-time text [RFC4103]. All PSAPs should accept G.711 A-law (and mu-Law in North America) encoded voice as described in [RFC3551]. Newer text forms are rapidly appearing, with Instant Messaging now very common, PSAPs should accept IM with at least "pager-mode" MESSAGE [RFC3428] as well as Message Session Relay Protocol [RFC4975]. Video may be important to support Video Relay Service (Sign language interpretation) as well as modern video phones. While it is desirable for media to be kept secure, preferably by use of Secure RTP [RFC3711], there is not yet consensus on how best to signal keying material for SRTP. As a consequence, no recommendation to support SRTP can be made yet for emergency calls. 15. Testing Since the emergency calling architecture consists of a number of pieces operated by independent entities, it is important to be able to test whether an emergency call is likely to succeed without actually occupying the human resources at a PSAP. Both signaling and media paths need to be tested since NATs and firewalls may allow the session setup request to reach the PSAP, while preventing the exchange of media. [I-D.ietf-ecrit-phonebcp] includes a description of an automated test procedure that validates routing, signaling and media path continuity. This test would be used within some random interval after boot time, and whenever the device location changes enough that a new PSAP mapping is returned from LoST. A manual operation for the test should also be possible. The PSAP needs to be able to control frequency and duration of the test, and since the process could be overused, it may temporarily or permanently suspend its operation. There is a concern associated with testing during a so-called "avalanche-restart" event where, for example a large power outage affects a large number of endpoints, that, when power is restored, all attempt to reboot and, possibly, test. Devices need to randomize their initiation of a boot time test to avoid the problem. 16. Security Considerations Security considerations for emergency calling have been documented in [RFC5069], and [I-D.barnes-geopriv-lo-sec]. 17. IANA Considerations This document has no actions for IANA. 18. Acknowledgements This draft was created from a draft-schulzrinne-sipping-emergency-arch-02 together with sections from draft-polk-newton-ecrit-arch-considerations-02. Design Team members participating in this draft creation include Hannes Tschofenig, Ted Hardie, Martin Dolly, Marc Linsner, Roger Marshall, Stu Goldman, Shida Schubert and Tom Taylor. Further comments and input were provided by Richard Barnes, Barbara Stark and James Winterbottom. 19. Informative References [I-D.barnes-geopriv-lo-sec] Barnes, R., Lepinski, M., Tschofenig, H., and H. Schulzrinne, "Security Requirements for the Geopriv"Additional Location System", draft-barnes-geopriv-lo-sec-02 (work in progress), February 2008. [I-D.ietf-ecrit-dhc-lost-discovery] Schulzrinne, H., Polk, J., and H. Tschofenig, "A Dynamic Host Configuration Protocol (DHCP) based Location-to- Service Translation Protocol (LoST) Discovery Procedure", draft-ietf-ecrit-dhc-lost-discovery-03Privacy Considerations", draft-barnes-geopriv-lo-sec-03 (work in progress), May 2008. [I-D.ietf-ecrit-lost] Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig, "LoST: A Location-to-Service Translation Protocol", draft-ietf-ecrit-lost-10 (work in progress), MayJuly 2008. [I-D.ietf-ecrit-phonebcp] Rosen, B. and J. Polk, "Best Current Practice for Communications Services in support of Emergency Calling", draft-ietf-ecrit-phonebcp-04draft-ietf-ecrit-phonebcp-06 (work in progress), FebruaryNovember 2008. [I-D.ietf-geopriv-http-location-delivery] Barnes, M., Winterbottom, J., Thomson, M., and B. Stark, "HTTP Enabled Location Delivery (HELD)", draft-ietf-geopriv-http-location-delivery-08draft-ietf-geopriv-http-location-delivery-11 (work in progress), JulyDecember 2008. [I-D.ietf-geopriv-lis-discovery] Thomson, M. and J. Winterbottom, "Discovering the Local Location Information Server (LIS)", draft-ietf-geopriv-lis-discovery-01draft-ietf-geopriv-lis-discovery-05 (work in progress), JuneDecember 2008. [I-D.ietf-geopriv-pdif-lo-profile] Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV PIDF-LO Usage Clarification, Considerations and Recommendations", draft-ietf-geopriv-pdif-lo-profile-11draft-ietf-geopriv-pdif-lo-profile-14 (work in progress), FebruaryNovember 2008. [I-D.ietf-sip-gruu] Rosenberg, J., "Obtaining and Using Globally Routable User Agent (UA) URIs (GRUU) in the Session Initiation Protocol (SIP)", draft-ietf-sip-gruu-15 (work in progress), October 2007. [I-D.ietf-sip-location-conveyance] Polk, J. and B. Rosen, "Location Conveyance for the Session Initiation Protocol", draft-ietf-sip-location-conveyance-10draft-ietf-sip-location-conveyance-12 (work in progress), FebruaryNovember 2008. [I-D.ietf-sip-outbound] Jennings, C. and R. Mahy, "Managing Client Initiated Connections in the Session Initiation Protocol (SIP)", draft-ietf-sip-outbound-15draft-ietf-sip-outbound-16 (work in progress), JuneOctober 2008. [I-D.ietf-sip-sips] Audet, F., "The use of the SIPS URI Scheme in the Session Initiation Protocol (SIP)", draft-ietf-sip-sips-08draft-ietf-sip-sips-09 (work in progress), FebruaryNovember 2008. [I-D.ietf-sipping-service-examples] Johnston, A., Sparks, R., Cunningham, C., Donovan, S., and K. Summers, "Session Initiation Protocol Service Examples", draft-ietf-sipping-service-examples-14draft-ietf-sipping-service-examples-15 (work in progress), FebruaryJuly 2008. [LLDP] IEEE, "IEEE802.1ab Station and Media Access Control", Dec 2004. [LLDP-MED] TIA, "ANSI/TIA-1057 Link Layer Discovery Protocol - Media Endpoint Discovery". [NENAi3TRD] NENA, "08-751 NENA i3 Technical Requirements for", 2006. [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. [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity within Trusted Networks", RFC 3325, November 2002. [RFC3428] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and D. Gurle, "Session Initiation Protocol (SIP) Extension for Instant Messaging", RFC 3428, December 2002. [RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer Method", RFC 3515, April 2003. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, July 2003. [RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004. [RFC3825] Polk, J., Schnizlein, J., and M. Linsner, "Dynamic Host Configuration Protocol Option for Coordinate-based Location Configuration Information", RFC 3825, July 2004. [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller Preferences for the Session Initiation Protocol (SIP)", RFC 3841, August 2004. [RFC3856] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", RFC 3856, August 2004. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [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. [RFC4190] Carlberg, K., Brown, I., and C. Beard, "Framework for Supporting Emergency Telecommunications Service (ETS) in IP Telephony", RFC 4190, November 2005. [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. [RFC4474] Peterson, J. and C. Jennings, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", RFC 4474, August 2006. [RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4 and DHCPv6) Option for Civic Addresses Configuration Information", RFC 4776, November 2006. [RFC4967] Rosen, B., "Dial String Parameter for the Session Initiation Protocol Uniform Resource Identifier", RFC 4967, July 2007. [RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message Session Relay Protocol (MSRP)", RFC 4975, September 2007. [RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for Emergency Context Resolution with Internet Technologies", RFC 5012, January 2008. [RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for Emergency and Other Well-Known Services", RFC 5031, January 2008. [RFC5069] Taylor, T., Tschofenig, H., Schulzrinne, H., and M. Shanmugam, "Security Threats and Requirements for Emergency Call Marking and Mapping", RFC 5069, January 2008. [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, "Transport Layer Security (TLS) Session Resumption without Server-Side State", RFC 5077, January 2008. [RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location Format for Presence Information Data Format Location Object (PIDF-LO)", RFC 5139, February 2008. [RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig, "LoST: A Location-to-Service Translation Protocol", RFC 5222, August 2008. [RFC5223] Schulzrinne, H., Polk, J., and H. Tschofenig, "Discovering Location-to-Service Translation (LoST) Servers Using the Dynamic Host Configuration Protocol (DHCP)", RFC 5223, August 2008. [WGS84] NIMA, "NIMA Technical Report TR8350.2, Department of Defense World Geodetic System 1984, Its Definition and Relationships With Local Geodetic Systems, Third Edition", July 1997. Authors' Addresses Brian Rosen NeuStar, Inc. 470 Conrad Dr Mars, PA 16046 US Email: email@example.com Henning Schulzrinne Columbia University Department of Computer Science 450 Computer Science Building New York, NY 10027 US Phone: +1 212 939 7042 Email: firstname.lastname@example.org URI: http://www.cs.columbia.edu James Polk Cisco Systems 3913 Treemont Circle Colleyville, Texas 76034 US Phone: +1-817-271-3552 Email: email@example.com Andrew Newton TranTech/MediaSolv 4900 Seminary Road Alexandria, VA 22311 US Phone: +1 703 845 0656 Email: firstname.lastname@example.org 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. 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