TBD H. Schulzrinne Internet-Draft Columbia U. Expires: September 24, 2004 March 26, 2004 Requirements for Session Initiation Protocol (SIP)-based Emergency Calls draft-ietf-ecrit-emergency-req-00 Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. 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 September 24, 2004. Copyright Notice Copyright (C) The Internet Society (2004). Abstract This document enumerates requirements for emergency calls placed by the public using voice-over-IP (VoIP) and general Internet multimedia systems, where Internet protocols are used end-to-end, from caller to public safety answering point (PSAP) answering the call. These requirements for end-to-end IP-based emergency calling address functional and security issues for determining the correct emergency address, for identifying the appropriate PSAP and for identifying the Schulzrinne Expires September 24, 2004 [Page 1] Internet-Draft Emergency requirements March 2004 caller and its current location. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . 6 4. General Requirements . . . . . . . . . . . . . . . . . . . . 8 5. Emergency Address . . . . . . . . . . . . . . . . . . . . . 9 6. Identifying the Caller Location . . . . . . . . . . . . . . 11 7. Identifying the Appropriate Emergency Call Center . . . . . 13 8. Identifying the Caller . . . . . . . . . . . . . . . . . . . 17 9. Call Setup and Call Features . . . . . . . . . . . . . . . . 18 10. Security Considerations . . . . . . . . . . . . . . . . . . 19 10.1 General Threats . . . . . . . . . . . . . . . . . . . . 19 10.2 Call Origin Identification . . . . . . . . . . . . . . . 19 10.3 Location Validation and Verification . . . . . . . . . . 20 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 21 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 12.1 Normative References . . . . . . . . . . . . . . . . . . . 22 12.2 Informative References . . . . . . . . . . . . . . . . . . 22 Author's Address . . . . . . . . . . . . . . . . . . . . . . 22 Intellectual Property and Copyright Statements . . . . . . . 23 Schulzrinne Expires September 24, 2004 [Page 2] Internet-Draft Emergency requirements March 2004 1. Introduction Users of telephone-like services expect to be able to call for emergency help, such as police, the fire department or an ambulance, regardless of where they are, what (if any) service provider they are using and what kind of device they are using. Unfortunately, the mechanisms for emergency calls that have evolved in the public circuit-switched telephone network (PSTN) are not quite appropriate for evolving IP-based voice, text and real-time multimedia communications. This document outlines some of the requirements that end systems and network elements such as SIP proxies need to satisfy in order to provide emergency call services that offer at least the same functionality as existing PSTN services, while hopefully making emergency calling more robust, cheaper to implement and multimedia-capable. In the future, users of other real-time and near real-time services may also expect to be able to summon emergency help. For example, instant messaging (IM) users may want to use such services. IM is particularly helpful for hearing-disabled users (RFC 3351 [2]) and in cases where bandwidth is scarce. For lack of a better term, we will use the term "caller" or "emergency caller" to refer to the person placing an emergency call or sending an emergency IM. Emergency callers and PSAPs expect calls to be completed reliably. Where possible, a callback number and the current caller location shouls be delivered to the PSAP to speed up emergency response and to limit prank calls. The emergency calls described in this document differ from the emergency telecommunications service (ETS) described in XXX. In ETS, relatively small numbers of emergency workers need to maintain communication even when parts of the infrastructure are destroyed or disabled. Emergency calls, on the other hand, are placed by civilians to call for emergency services such as fire, ambulance and police services. Thus, these two services are complementary. 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 at the emergency call taker who also uses IP-based communication facilities. Other hybrid architectures, such as trunk replacement or IP-based emergency calls terminating on gateways, are beyond the scope of this document. There is a third approach, where SIP-originated calls terminate on a PSTN gateway in each emergency calling area. This architecture is left for future consideration and discussed in other standardization organizations, such as NENA, as it is strongly dependent on the Schulzrinne Expires September 24, 2004 [Page 3] Internet-Draft Emergency requirements March 2004 currently-deployed emergency services network architecture. End-to-end emergency calls originate on an Internet device, traverse IP networks and terminate on an IP-capable PSAP (iPSAP). As noted, emergency calls need to be identified as such Section 5 and be routed to the appropriate emergency call center (see Section 7). The PSAP needs to determine who (Section 8) placed the call from where (Section 6). Emergency calls may not be subject to access restrictions placed on non-emergency calls. Also, some call features may interfere with emergency calls, particularly if triggerd accidentally (Section 9). Schulzrinne Expires September 24, 2004 [Page 4] Internet-Draft Emergency requirements March 2004 2. Terminology In this document, the key words "MUST", "MUSTNOT", "REQUIRED", "SHALL", "SHALLNOT", "SHOULD", "SHOULDNOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and indicate requirement levels for compliant implementations. Since a requirements document does not directly specify an implementable protocols, these compliance labels should be read as indicating requirements for the protocol or architecture, rather than an implementation. Schulzrinne Expires September 24, 2004 [Page 5] Internet-Draft Emergency requirements March 2004 3. Definitions Application (Voice) Service Provider (ASP, VSP): The organization that provides voice or other application-layer services, such as call routing, a SIP URI or PSTN termination. This organization can be a private individual, an enterprise, a government or a service provider. We avoid the term voice service provider as emergency calls are likely to use other media, including text and video, in the future. For a particular user, the ASP may not be the same organization as the IAP or ISP. Basic emergency service: Basic emergency service allows a user to reach a PSAP serving its current location, but the PSAP may not be able to determine the identity or geographic location of the caller (except by having the call taker ask the caller). Call taker: A call taker is an agent, typically a government employee, at the PSAP that accepts calls and may dispatch emergency help. (Sometimes the functions of call taking and dispatching are handled by different groups of people, but these divisions of labor are not generally visible to the outside and thus do not concern us here.) ECC (emergency control center): Facilities used by emergency organizations to accept and handle emergency calls. A PSAP (below) forwards emergency calls to the emergency control center, which dispatches polic, fire, rescue and other emergency services. An ECC serves a limited geographic area. A PSAP and ECC can be combined into one facility (ETSI SR 002 180 definition). We assume that the ECC is reachable by IP-based protocols, such as SIP for call signaling and RTP for media. Enhanced emergency service: Enhanced emergency services add the ability to identify the caller identity and/or caller location to basic emergency services. (Sometimes, only the caller location may be known, e.g., from a public access point that is not owned by an individual.) Internet access provider (IAP): An organization that provides physical network connectivity to its customers or users, e.g., through digital subscriber lines, cable TV plants, Ethernet, leased lines or radio frequencies. This entity may or may not also provide IP routing, IP addresses, or other Internet protocol services. Examples of such organizations include telecommunication carriers, municipial utilities, larger enterprises with their own network infrastructure, and government organizations such as the military. Internet service provider (ISP): An organization that provides IP network-layer services to its customers or users. This entity may or may not provide the physical-layer and layer-2 connectivity, such as fiber or Ethernet. Schulzrinne Expires September 24, 2004 [Page 6] Internet-Draft Emergency requirements March 2004 Location validation: A caller location is considered valid if the civic or geospatial address exists and can be mapped to one or more PSAPs. Location validation ensures that a location is valid. PSAP (public safety answering point): Physical location where emergency calls are received under the responsibility of a public authority. (This terminology is used by both ETSI, in ETSI SR 002 180, and NENA.) In the United Kingdom, PSAPs are called Operator Assistance Centres, in New Zealand Communications Centres. We assume that the PSAP is reachable by IP-based protocols, such as SIP for call signaling and RTP for media. Schulzrinne Expires September 24, 2004 [Page 7] Internet-Draft Emergency requirements March 2004 4. General Requirements Below, we summarize high-level architectural requirements that guide some of the component requirements detailed later in the document. G1: No voice service provider: The caller may not have a voice service provider, i.e., a corporate entity that provides voice services as a business. 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 not be a telecommunication provider. G2: International: It must be possible for a device or software developed or purchased in one country to place emergency calls in another country. System components should not be biased towards a particular set of emergency numbers or languages. Also, different countries have evolved different ways of organizing emergency services, e.g., either centralizing them or having smaller regional subdivisions such as United States counties or municipalities handle emergency calls. The architecture and protocols developed must be able to support such diverse organizational structures. G3: Distributed administration: Once common standards are established, it must be 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, ASPs, IAPs or other participants. G4: Multimedia: Emergency calling must support a variety of media, not just voice. Such media include conversational text, instant messaging and video. In addition, it should be possible to convey telemetry data, such as data from automobile crash sensors. Schulzrinne Expires September 24, 2004 [Page 8] Internet-Draft Emergency requirements March 2004 5. Emergency Address The emergency address is used by the emergency caller to declare a call to be an emergency call and to guide the call to a PSAP. The emergency address could a be "sip", "sips" or "tel" URI, or some other, yet-to-be-defined URI scheme. A1: Universal: Each device and all network elements MUST recognize one or more global emergency call identifiers, regardless of the location of the device, the service provider used (if any) or other factors. Motivation: SIP and other call signaling protocols are not specific to one country or service provider and devices are likely to be used across national or service provider boundaries. Since services such as disabling mandatory authentication for emergency calls (S1) requires the cooperation of outbound proxies, the outbound proxy has to be able to recognize the emergency address and be assured that it will be routed as an emergency call. Thus, a simple declaration on a random URI that it is an emergency call will likely lead to fraud and possibly attacks on the network infrastructure. A universal address also makes it possible to create user interface elements that are correctly configured without user intervention. UA features could be made to work without such an identifier, but the user interface would then have to provide an unambiguous way to declare a particular call an emergency call. A2: Local: Since many countries have already deployed national emergency numbers, such as 911 in North America and 112 in large parts of Europe, UAs, proxies and call routers MUST recognize local emergency numbers. In addition, they SHOULD recognize emergency numbers that are found elsewhere. Motivation: The latter requirement is meant to help travelers that may not know the local emergency number and instinctively dial the number they are used to from home. However, it is unlikely that all systems could be programmed to recognize any emergency number used anywhere as some of these numbers are used for non-emergency purposes, in particular extensions and service numbers. A3: Recognizable: Emergency calls MUST be recognizable by user agents, proxies and other network elements. To prevent fraud, an address identified as an emergency number for call features or authentication override MUST also cause routing to a PSAP. A4: Minimal configuration: Any local emergency numbers SHOULD be configured automatically, without user intervention. Motivation: A new UA "unofficially imported" into an organization from elsewhere should have the same emergency capabilities as one officially installed. Schulzrinne Expires September 24, 2004 [Page 9] Internet-Draft Emergency requirements March 2004 A5: Secure configuration: Devices SHOULD be assured of the correctness of the local emergency numbers that are automatically configured. Motivation: If we assume a fixed, global emergency service identifier that requires no configuration and only configure local "traditional" emergency numbers, users are not likely to suddenly dial some random number if a rogue configuration server introduces this as an additional emergency number. The ability to override all locally configured emergency number is of more concern. A6: Backwards-compatible: Existing devices that predate the specification of emergency call-related protocols and conventions MUST be able reach a PSAP. Schulzrinne Expires September 24, 2004 [Page 10] Internet-Draft Emergency requirements March 2004 6. Identifying the Caller Location The caller location needs to be identified for two purposes, namely to route the call to the appropriate PSAP and to display the caller location to the call taker to simplify dispatching emergency assistance to the correct location. This section supplements the requirements outlined in RFC 3693 [3]. Thus, the requirements enumerated there are not repeated here. In general, we can distinguish three modes of operation: UA-inserted: The caller's user agent inserts the location information, derived from sources such as GPS, DHCP or link-layer announcements (LLDP). UA-referenced: The caller's user agent provides a reference, via a permanent or temporary identifier, to the location which is stored by a location service somewhere else and then retrieved by the PSAP. Proxy-inserted: A proxy along the call path inserts the location or location reference. L1: Multiple location services: For UA-referenced locations, PSAPs MUST be able to access different location providers. The location provider may be tied to the ASP, IAP or ISP or may be independent of these entities. Motivation: This requirement avoids that all users have to rely on a single location service provider. This requirement is hard to avoid if there are no traditional national application-layer service providers. L2: Civic and geographic: Where available, both civic (street address) and geographic (longitude/latitude) information SHOULD be provided to the PSAP. Motivation: While geographic information can usually be translated into civic coordinates, some coordinates, such as building numbers and floors, are more easily provided as civic coordinates since they do not require a detailed surveying operation. For direct location determination, it may also be easier for the user to check civic coordinates for correctness. L3: Location source identification: Sources and transformations of location data MUST be indicated to the PSAP. Transformations include conversions across datums or from civic to geospatial coordinates. Motivation: This allows the PSAP to better judge the reliability and accuracy of the data and track down problems. L4: Certifiable: In some cases, the source and generation time of the location object used for call routing and caller location display must be verifiable, e.g., by a digital signature. The security requirements describe this in more detail. Schulzrinne Expires September 24, 2004 [Page 11] Internet-Draft Emergency requirements March 2004 L5: Multiple addresses: The location of the caller may be described by multiple addresses, either because they provide both civic and geospatial coordinates or because different entities differ in their assessment of where the caller is located. L6: Validation: It must be possible to validate an address prior to its use in an actual emergency call. Note that this may be considered part of requirement I16 (Testable). Schulzrinne Expires September 24, 2004 [Page 12] Internet-Draft Emergency requirements March 2004 7. Identifying the Appropriate Emergency Call Center From the previous section, we take the requirement of a single (or small number of) emergency addresses which are independent of the caller's location. However, since for reasons of robustness, jurisdiction and local knowledge, PSAPs only serve a limited geographic region, having the call reach the correct PSAP is crucial. While a PSAP may be able to transfer an errant call, any such transfer is likely to add tens of seconds to call setup latency and is prone to errors. (In the United States, there are about 6,100 PSAPs.) Several terms are used for causing the call signaling to reach the geographically appropriate PSAP. This has been referred to as call routing, (PSAP) lookup or location mapping, all capturing aspects of the problem. There appear to be two basic architectures for translating an emergency address into the correct IPSAP. We refer to these as caller-based and mediated. In caller-based resolution, the caller's user agent consults a directory and determines the correct IPSAP based on its location. We assume that the user agent can determine its own location, either by knowing it locally or asking some third party for it. A UA could conceivably store a complete list of all PSAPs across the world, but that would require frequent synchronization with a master database as PSAPs merge or jurisdictional boundaries change. For mediated resolution, a call signaling server, such as a SIP (outbound) proxy or redirect server, performs this function. Note that the latter case includes the architecture where the call is effectively routed to a copy of the database, rather than having some non-SIP protocol query the database. 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 traveller may, for example, accidentally or intentionally configure its home proxy server as its outbound proxy server, even while far away from home.) Note that the first proxy doing the translation may not be in the same geographic area as the UA placing the emergency call. The resolution may take place well before the actual emergency call is placed, or at the time of the call. The problem is harder than for traditional web or email services. There, the originator knows which entity it wants to reach, Schulzrinne Expires September 24, 2004 [Page 13] Internet-Draft Emergency requirements March 2004 identified by the email address or HTTP URL. However, the emergency caller only dialed an emergency address. Depending on the location, any of several ten thousand PSAPs around the world could be valid. In addition, the caller probably does not care which specific PSAP answers the call, but rather that it be an accredited PSAP, e.g., one run by the local government authorities. (Many PSAPs are run by private entities. For example, universities and corporations with large campuses often have their own emergency response centers.) I1: Correct PSAP: The system MUST reach the correct PSAP, that is, a PSAP that serves the location of the caller. In particular, the location determination should 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. I2: Early routing: In mediated mode, the first proxy server along a request path MUST attempt to route the call to the appropriate IPSAP. Motivation: Proxy servers close to the caller can be expected to have better call routing knowledge, particularly if international boundaries are being crossed. I3: Multi-stage: The user agent or a call routing entity close to the caller may not be able to deliver the call directly to the serving PSAP, but rather to an intermediary that it turn uses caller location information to route the call closer to the appropriate PSAP. I4: Choice of IPSAPs: The system SHOULD offer the emergency caller a choice as to whether he wants to reach a local private emergency response center, e.g., on a corporate campus, or the government-run emergency call center responsible for his current location. Motivation: This choice is often, but not always, provided today. For example, in some cases, the local campus emergency center is reachable by a different number or 9-911 reaches the external PSAP, while 911 reaches campus security. I5: Assuring IPSAP identity: The emergency caller SHOULD be able to determine conclusively that he has reached an accredited emergency call center. Motivation: This requirement is meant to address the threat that a rogue, possibly criminal, entity pretends to accept emergency calls. Implementations SHOULD allow callers to proceed, with appropriate warnings or user confirmations, if the identity of the destination IPSAP cannot be verified. Motivation: Verification can fail for any number of reasons, such as lack of a common certificate chain, especially when traveling, call forwarding, or the expiration of certificates. Accreditation, e.g., in the case of corporate or university Schulzrinne Expires September 24, 2004 [Page 14] Internet-Draft Emergency requirements March 2004 campuses, may not exist. I6: Traceable resolution: Particularly for mediated resolution, the caller SHOULD be able to definitively and securely determine who provided the resolution answer. I7: Assuring directory identity: The querier (UA or server) MUST be able to assure that it is querying the intended directory. I8: Query response integrity: The querier MUST be able to be confident that the query or response has not been tampered with. I9: Assuring update integrity: Any update mechanism for the directory MUST ensure that only authorized users can change directory information. An audit trail MUST be provided. I10: Call setup latency: The directory lookup SHOULD add minimal delay to the call setup. Since outbound proxies will likely be asked to resolve the same geographic coordinates repeatedly, a suitable time-limited caching mechanism SHOULD be supported (see also "Ix"). I11: Multiple directories: A UA or proxy SHOULD be able to use multiple different directories to resolve the emergency address. We do not assume that a single directory has worldwide or even nationwide coverage. Motivation: This allows competing or regional data sources. I12: Referral: All directories SHOULD refer out-of-area queries to an appropriate default or region-specific directory. Motivation: This requirement alleviates the potential for misconfigurations to cause calls to fail, particularly for caller-based queries. I13: Multiple query protocols: It MAY be useful if directories support multiple query protocols, such as SIP (for proxying), IRIS, LDAP, a SOAP-based query and others. A mandatory-to-implement protocol MUST be specified and an over-abundance of similarly-capable choices appears undesirable for interoperability. Motivation: It appears likely that the resolution mechanism will be needed by a variety of session protocols and user applications. I14: Robustness: The resolution mechanism MUST allow to deploy systems that are robust in the face of partial network and directory server failures. Caching MAY be used to mitigate temporary unavailability of directories or network connectivity. As long as the PSAP is reachable by the caller, a temporary failure of the lookup and routing mechanism should not prevent completion of the emergency call. I15: Incrementally deployable: An Internet-based emergency call system MUST be able to deployed incrementally. In the initial stages of deployment, an emergency call may not reach the optimal PSAP. Schulzrinne Expires September 24, 2004 [Page 15] Internet-Draft Emergency requirements March 2004 I16: Testable: A user SHOULD be able to test whether a particular address reaches the appropriate PSAP, without actually causing emergency help to be dispatched or consuming PSAP call taker resources. Such tests MUST indicate the source of any problems, including the validity and plausibility of civic and geospatial location addresses. This requirement also allows address validation. Schulzrinne Expires September 24, 2004 [Page 16] Internet-Draft Emergency requirements March 2004 8. Identifying the Caller Enhanced emergency call systems provide the PSAP with the identity and location of the caller. In PSTN-based systems, the identity is represented by the number of the customer premises equipment (CPE) the call is placed from. In a SIP-based system, we have two distinct identities, namely the network address of the user agent (SIP Contact header field) and the identity (name and/or AOR) of the person using the user agent. Depending on the circumstances, only one of them may be available. For example, from a public terminal (Internet payphone), only the Contact address may be useful. In most jurisdictions, callers do not have a choice as to whether they want to reveal their location or identity; such disclosure is typically mandated by law. C1: Identity: The system SHOULD allow (but not force) to identify both the caller's identity and his or her terminal network address. C2: Privacy override: The end system MUST be able to automatically detect that a call is an emergency call so that it can override any privacy settings that conflict with emergency calling. (Whether this override can be configured by the user or is considered a condition of service is considered a legal matter, not a protocol issue.) Motivation: Since emergency calls are often placed by children, by people using somebody else's end system or by people in panic, any configuration should be automated rather than relying on user interaction at the time of the call. Delaying a call until the user discovers that they have to answer some screen prompt or deal with a voice prompt in an unfamiliar language is likely to lead to large call setup delays or call failures. This does not preclude that end systems can allow, on a call-by-call basis, to configure special call parameters, e.g., to enable anonymous tip lines. Schulzrinne Expires September 24, 2004 [Page 17] Internet-Draft Emergency requirements March 2004 9. Call Setup and Call Features S1: Authentication override: In many jurisdictions, emergency calls can be placed by any device, regardless of whether it has subscribed for service. Similarly, outbound proxies and other call filtering elements MUST be able to be configured so that they allow unauthenticated emergency calls. S2: Mid-call features: The end system MUST be able to recognize an emergency call and allow configuration so that certain call features are not triggered accidentally. For example, it may be inappropriate to transfer the PSAP or put it on hold. An end system MAY make it more difficult to disconnect an on-going emergency call or accept other incoming calls while in an emergency call. Motivation: Call transfer initiated by the emergency caller is likely only to be a problem if a PSTN gateway or B2BUa is in the call path. It is not clear how much effort should be expended on preventing intentional, as opposed to accidental, disconnection, since callers can typically find physical-layer means to terminate the call. This feature is not generally available in the PSTN. For example, ANSI T1.628-2001 states that "E9-1-1 Call hold is an optional network feature provided to a PSAP which prevents a caller from disconnecting an ESC. .... However, there is no DSS1 or SS7 support for this capability at this time." S3: Testable: Users SHOULD be able to test the ability to place an emergency call without actually invoking an emergency response or tying up emergency call take resources. Motivation: This capability is unfortunately missing from the current PSTN. S4: Integrity: Implementations MUST provide mechanisms that ensure the integrity of SIP protocol component that are crucial to providing reliable emergency call service. (This requirement implies authentication of the caller to allow integrity protection of the request and authentication of the PSAP to allow integrity protection of responses.) Schulzrinne Expires September 24, 2004 [Page 18] Internet-Draft Emergency requirements March 2004 10. Security Considerations 10.1 General Threats Confidentiality, integrity and authentication are core requirements for multiple aspects of emergency calling. Threats exist at the infrastructure and individual call level. Security threats are identified throughout this document. An adversary could corrupt call information or PSAP resolution to cause emergency calls to fail subtly, without the caller necessarily noticing. This can be done on a call-by-call basis or by corrupting elements that perform the resolution, including the directory described in Section 7, Internet routing tables or DNS. (Obviously, there are typically other ways to make emergency calls fail completely, an approach phone-wire cutting burglars have practiced for years. However, the ability to spoof a PSAP requires physical access to the PSTN cable plant, while this may not be required in the IP case.) Here, we do not consider attacks on the emergency call infrastructure itself. The techniques for dealing with such attacks are likely to be similar as those for protecting other network infrastructure, although the stakes may well be higher. In particular, layered defenses against denial-of-service attacks, including return routability checks, are likely to be part of the defensive arsenal. 10.2 Call Origin Identification To discourage prank calls and to avoid dispatching emergency responders to such calls, identifying the caller either during or after a call is helpful. Such identification can answer one or more of the following questions: o Which IP address issued the call setup request? o Which proxies, identified by IP addresses or URIs, processed the call on its way to the PSAP? o Did the SIP URI claimed in the SIP From header field actually place the call? o What is the legal name and residence street address of the person using that SIP URI? (This address may legitimately differ from the current caller location and may be the billing address of the caller, for example.) o Did the domain in the SIP From header field authorize the caller to use that user name? Schulzrinne Expires September 24, 2004 [Page 19] Internet-Draft Emergency requirements March 2004 10.3 Location Validation and Verification As discussed earlier (Section 3), location validation ensures that an address exists and is mappable to a PSAP. A valid address, however, does not imply that the call actually originated from that location. We refer to location verification as the assurance that the call was placed at the location claimed, including any error margins provided. Verifying a location is generally more difficult than location validation as there is currently no generally trusted service that can vouch for the location of the caller. In some cases, AIPs or ISPs may be able to indicate the location of the caller with high confidence and they may possess cryptographic certificates that are trusted by the PSAP. This may not require a global certification authority (CA), as a regional PSAP typically only deals with a modest number of larger enterprises and thus could obtain their public keys even if self-signed. However, even if the AIP or ISP provides a signed location, it is difficult to ensure that such a signed location object is only used for calls from that location, as it will have to be copied from a location delivery protocol to the call signaling protocol. For example, a third party could obtain such a signed location object and use it elsewhere. Naturally, timestamps will restrict such useage to the order of minutes or hours, depending on how often location information is updated. A PSAP may want to be able to answer the following questions: o Who originally provided this particular location information? o Did the call originate from that particular geospatial or civic address and who says so and how do they know? Schulzrinne Expires September 24, 2004 [Page 20] Internet-Draft Emergency requirements March 2004 11. Acknowledgments James Polk provided helpful comments on an earlier version of this document. Schulzrinne Expires September 24, 2004 [Page 21] Internet-Draft Emergency requirements March 2004 12. References 12.1 Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 12.2 Informative References [2] Charlton, N., Gasson, M., Gybels, G., Spanner, M. and A. van Wijk, "User Requirements for the Session Initiation Protocol (SIP) in Support of Deaf, Hard of Hearing and Speech-impaired Individuals", RFC 3351, August 2002. [3] Cuellar, J., Morris, J., Mulligan, D., Peterson, J. and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. [4] National Emergency Number Assocation, "NENA technical information document on the interface between the E9-1-1 service providers network and the Internet protocol (IP) PSAP", NENA NENA-08-501, February 2003. Author's Address Henning Schulzrinne Columbia University Department of Computer Science 450 Computer Science Building New York, NY 10027 US Phone: +1 212 939 7004 EMail: hgs+ecrit@cs.columbia.edu URI: http://www.cs.columbia.edu Schulzrinne Expires September 24, 2004 [Page 22] Internet-Draft Emergency requirements March 2004 Intellectual Property Statement 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. 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