--- 1/draft-ietf-ecrit-requirements-01.txt 2006-02-04 17:14:22.000000000 +0100 +++ 2/draft-ietf-ecrit-requirements-02.txt 2006-02-04 17:14:22.000000000 +0100 @@ -1,19 +1,19 @@ ecrit H. Schulzrinne Internet-Draft Columbia U. -Expires: April 24, 2006 R. Marshall, Ed. +Expires: July 3, 2006 R. Marshall, Ed. TCS - October 21, 2005 + December 30, 2005 Requirements for Emergency Context Resolution with Internet Technologies - draft-ietf-ecrit-requirements-01.txt + draft-ietf-ecrit-requirements-02.txt Status of this Memo 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 becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that @@ -24,55 +24,55 @@ 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 April 24, 2006. + This Internet-Draft will expire on July 3, 2006. Copyright Notice Copyright (C) The Internet Society (2005). 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 3. Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 4. High-Level Requirements . . . . . . . . . . . . . . . . . . . 10 - 5. Identifying the Caller Location . . . . . . . . . . . . . . . 12 - 6. Emergency Identifier . . . . . . . . . . . . . . . . . . . . . 14 - 7. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 16 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 20 - 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 21 - 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22 - 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 - 11.1. Normative References . . . . . . . . . . . . . . . . . . 23 - 11.2. Informative References . . . . . . . . . . . . . . . . . 23 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 - Intellectual Property and Copyright Statements . . . . . . . . . . 25 + 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 3. Basic Actors . . . . . . . . . . . . . . . . . . . . . . . . . 8 + 4. High-Level Requirements . . . . . . . . . . . . . . . . . . . 11 + 5. Identifying the Caller Location . . . . . . . . . . . . . . . 13 + 6. Emergency Identifier . . . . . . . . . . . . . . . . . . . . . 15 + 7. Mapping Protocol . . . . . . . . . . . . . . . . . . . . . . . 17 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 22 + 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 23 + 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25 + 11.1. Normative References . . . . . . . . . . . . . . . . . . 25 + 11.2. Informative References . . . . . . . . . . . . . . . . . 25 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26 + Intellectual Property and Copyright Statements . . . . . . . . . . 27 1. Introduction Users of both voice-centric (telephone-like) and non voice type services (e.g. text messaging for hearing disabled users, (RFC 3351 - [4]) have an expectation to be able to initiate a request for help in + [5]) have an expectation to be able to initiate a request for help in case of an emergency. Unfortunately, the existing mechanisms to support emergency calls that have evolved within the public circuit-switched telephone network (PSTN), are not appropriate to handle evolving IP-based voice, text and real-time multimedia communications. This document outlines the key requirements that IP-based end systems and network elements, such as SIP proxies, need to satisfy in order to provide emergency call services, which at a minimum, offer the same functionality as existing PSTN services, with the additional overall @@ -95,39 +95,48 @@ Identification of the caller, while not incompatible with the requirements for messaging outlined within this document, is not currently considered within the scope of the ECRIT charter, and is therefore, left for a future draft to describe. Note: Location is required for two separate purposes, first, to route the call to the appropriate PSAP and second, to display the caller's location to the call taker for help in dispatching emergency assistance to the correct location. + Ideally, the mapping protocol would yield a URI from a preferred set + of URIs (e.g. sips:uri; sip:uri), which would allow an emergency call + to be completed using IP end-to-end (possibly via the Internet). + Despite this goal, some PSAPs may not immediately have IP based + connectivity, and therefore it is imperative that the URI scheme not + be fixed, in order to ensure support for a less preferred set of + URIs, such as a TEL URI which may be used to Complete a call over the + PSTN. + 2. Terminology In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "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 a protocol to implement, these compliance labels should be read as indicating requirements for the protocol or architecture, rather than an implementation. 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. Application Service Provider (ASP): The organization or entity that provides application-layer services, which may include voice (see - term Voice Service Provider). This entity can be a private + "Voice Service Provider"). This entity can be a private individual, an enterprise, a government, or a service provider. An ASP is defined as something more general than a Voice Service Provider, since emergency calls are sometimes likely to use other media, including text and video. Note: For a particular user, the ASP may or may not be the same organization as the IAP and/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). @@ -135,28 +144,28 @@ call taker: A call taker is an agent at the PSAP that accepts calls and may dispatch emergency help. (Sometimes the functions of call taking and dispatching are handled by different groups of people, but these divisions of labor are not generally visible to the outside and thus do not concern us here.) civic location: A described location based on some defined grid, such as a jurisdictional, postal, metropolitan, or rural reference system (e.g. street address). - directory service: A network service which uses a distributed - directory protocol to provide information about the PSAP, or - intermediary which knows about the PSAP, and is used to assist in - routing an emergency call. + mapping service: A network service which uses a distributed mapping + protocol to provide information about the PSAP, or intermediary + which knows about the PSAP, and is used to assist in routing an + emergency call. - emergency address: The sip:uri, sips:uri, or tel:uri which represents - the address of the PSAP useful for the completion of an emergency - call. + emergency address: The uri scheme (e.g. sip:uri, sips:uri, xmpp:uri, + im:uri, etc.) which represents the address of the PSAP useful for + the completion of an emergency call. emergency caller: The user or user device entity which sends his/her location to another entity in the network. emergency identifier: The numerical and/or text identifier which is supplied by a user or a user device, which identifies the call as an emergency call and is translated into an emergency address for call routing and completion. enhanced emergency service: Enhanced emergency services add the @@ -166,37 +175,39 @@ an individual.) ESRP (Emergency Services Routing Proxy): An ESRP is a call routing entity that invokes the location-to-URL mapping, which in turn may return either the URL for another ESRP or the PSAP. (In a SIP system, the ESRP would typically be a SIP proxy, but could also be a Back-to-back user agent (B2BUA). geographic location: A reference to a locatable point described by a set of defined coordinates within a geographic coordinate system, - (e.g. lat/lon within WGS-84 datum) + (e.g. lat/lon within the WGS-84 datum) Internet Attachment 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, municipal utilities, larger + leased lines or radio frequencies. Examples of such organizations + include telecommunication carriers, municipal utilities, larger enterprises with their own network infrastructure, and government organizations such as the military. Internet Service Provider (ISP): An organization that provides IP network-layer services to its customers or users. This entity may or may not provide the physical-layer and layer-2 connectivity, such as fiber or Ethernet. + Local Emerency Identifier: An emergency identifier which is + recognized from within a geographic or jurisdictional area from + which an emergency request is initiated. + location: A geographic identification assigned to a region or feature based on a specific coordinate system, or by other precise information such as a street number and name. In the geocoding process, the location is defined with an x,y coordinate value according to the distance north or south of the equator and east or west of the prime meridian. location validation: A caller location is considered valid if the civic or geographic location is recognizable within an acceptable location reference systems (e.g. USPS, WGS-84, etc.), and can be @@ -220,41 +231,47 @@ 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. Within this document, it is assumed, unless stated otherwise, that PSAP is that which supports the receipt of emergency calls over IP. It is also assumed that the PSAP is reachable by IP-based protocols, such as SIP for call signaling and RTP for media. + Universal Identifier: An emergency identifier which is recognized by + any compatible endpoint, from any geographic location as useful + for initiating an emergency request. A general approach to using + universal identifiers is outlined in the service URN draft + (I-D.schulzrinne-sipping-service [4]). + Voice Service Provider (VSP): A specific type of Application Service Provider which provides voice related services based on IP, such as call routing, a SIP URI, or PSTN termination. 3. Basic Actors In order to support emergency services covering a large physical area various infrastructure elements are necessary: Internet Attachment Providers, Application/Voice Service Providers, PSAPs as endpoints - for emergency calls, directory services or other infrastructure + for emergency calls, mapping services or other infrastructure elements that assist in during the call routing and potentially many other entities. This section outlines which entities will be considered in the routing scenarios discussed. Location Information +-----------------+ |(1) |Internet | +-----------+ v |Attachment | | | - +-----------+ |Provider | | Directory | + +-----------+ |Provider | | Mapping | | | | (3) | | Service | | Emergency |<---+-----------------+-->| | | Caller | | (2) | +-----------+ | |<---+-------+ | ^ +-----------+ | +----|---------+------+ | ^ | | Location | | | | | | Information<-+ | | | +--+--------------+ |(8) | | (5) | | +-----------v+ | | | (4) | |Emergency | | | @@ -302,41 +319,44 @@ Below, we describe various interactions between the entities shown in Figure 1 are described: o (1) Location information might be available to the end host itself. o (2) Location information might, however, also be obtained from the Internet Attachment Provider (e.g., using DHCP or application layer signaling protocols). - o (3) The Emergency Caller might need to consult a directory service - to determine the PSAP that is appropriate for the physical location - of the emergency caller (and considering other attributes such as a + o (3) The Emergency Caller might need to consult a mapping service to + determine the PSAP that is appropriate for the physical location of + the emergency caller (and considering other attributes such as a certain language support by the Emergency Call Takers). o (4) The Emergency Caller might get assistance for emergency call routing by infrastructure elements (referred as Emergency Call Routing Support entities). In case of SIP these entities are proxies. o (5) Individual Emergency Call Routing Support entities might need - to consult a directory servic to determine where to route the + to consult a mapping service to determine where to route the emergency call. o (6) The Emergency Call Routing Support entities need to finally forward the call, if infrastructure based emergency call routing is used. o (7) The emergency caller might interact directly with the PSAP without any Emergency Call Routing Support entities. + o (8) Location Information is used by emergency call routing entities + to determine appropriate PSAP mapping. + 4. High-Level Requirements Below, we summarize high-level architectural requirements that guide some of the component requirements detailed later in the document. Re1. Application Service Provider: The existence of an Application Service Provider (ASP) MUST NOT be assumed. Motivation: The caller may not have a application/voice service provider. For example, a residence may have its own DNS domain @@ -365,21 +385,21 @@ 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. Re4. Multiple Modes: Multiple communication modes, such as audio, video and text messaging MUST be supported. Motivation: In PSTN, voice and text telephony (often called TTY or textphone in North America ) are the only commonly supported media. Emergency calling must support a variety of media. Such - media should include voice, conversational text (RFC 4103 [6]), + media should include voice, conversational text (RFC 4103 [7]), instant messaging and video. Re5. Alternate Mapping Sources: The mapping protocol SHOULD allow for alternative redundant sources of mapping information, possibly of different degrees of currency. Motivation: This provides the possibility of having available alternative sources of mapping information when the normal source is unavailable or unreachable, without specifying the means by which the alternative source is created or updated. @@ -389,27 +409,28 @@ without special emergency extensions) unless an error is returned. Motivation: The format of the output returned by the mapping protocol is in a standard format for communication protocol. For example, it should return something SIP specific (e.g. URI), that any SIP capable phone would be able to use if used in a SIP context. Special purpose URIs would not be understood by "legacy" SIP devices since they do not have knowledge about the mapping protocol, and therefore are not to be used. - Re7. Relay Services: It SHOULD be possible to involve relay - services in the call for translation between different modes. + Re7. Ubiquiteous Triggering: It MUST be possible to invoke the + mapping protocol at any time, from any location, by any client + which supports the mapping protocol. - Motivation: It should be possible to connect the relay service so - that the direct flow of media to the emergency service is - maintained. In addition, it should be possible to convey - telemetry data, such as data from automobile crash sensors. + Motivation: While end devices are the typical initiators of + mapping service requests, it is also expected that other mapping + clients, such as relays, 3rd party devices, PSAPs, etc. may also + trigger a mapping request. Re8. PSAP Identification: The mapping information MUST be available without having to enroll with a service provider. Motivation: The mapping server may well be operated by a service provider, but access to the server offering the mapping must not require use of a specific ISP or VSP. 5. Identifying the Caller Location @@ -424,53 +445,63 @@ 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. - Lo1. Validation of civic location: It MUST be possible to validate - an civic location prior to its use in an actual emergency call. + Lo1. Validation of Civic Location: It MUST be possible to validate a + civic location prior to its use in an actual emergency call. Motivation: Location validation provides an opportunity to help assure ahead of time, whether successful mapping to the appropriate PSAP will likely occur when it is required. Validation may also help to avoid delays during emergency call setup due to invalid locations. - Lo2.: Validation of a civic location MUST NOT be required to enable - any feature that is part of the emergency call process. + Lo2. Limits to Validation: Validation of a civic location MUST NOT + be required to enable any feature that is part of the emergency + call process. Motivation: In some cases, (based on a variety of factors), a civic location may not be considered valid. This fact should not result in the call being dropped or rejected by any entity along the signaling path to the PSAP. Lo3. Reference Datum: The mapping server MUST understand WGS-84 coordinate reference system and may understand other reference systems. Lo4. Location Provided: An Emergency Services Routing Proxy (ESRP) MUST NOT remove location information after performing location based routing. Motivation: The ESRP and the PSAP use the same location information object but for a different purpose. Therefore, the PSAP still requires the receipt of information which represents the end device's location. + Lo5. 3D Sensitive Mapping: The mapping protocol MUST accept either a + 2D or 3D mapping request, and return an appropriate result, based + on which type of input is used. + + Motivation: It is expected that provisioning systems will accept + both 2D and 3D data. When a 3D request is presented to an area + only defined by 2D data, the mapping result would be the same as + if the height/altitude dimension was omitted on the request." + 6. Emergency Identifier - Id1. Universal Identifier - Setup: One or more universal emergency + Id1. Universal Identifier Setup: One or more universal emergency identifiers MUST be recognized by any device or network element for call setup purposes Motivation: There must be some way for any device or element to recognize an emergency call throughout the call setup. This is regardless of the device location, the application (voice) service provider used (if any at all), or of any other factor. Examples of these might include: 911, 112, and sos.*. Id2. Universal Identifier Resolution: Where multiple emergency @@ -478,34 +509,33 @@ identifier separately, based on the specific type of emergency help requested. Motivation: Some jurisdictions may have multiple types of emergency services available at the same level, (e.g. fire, police, ambulance), in which case it is important that any one could be selected directly. Id3. Emergency Marking: Any device in the signaling path that recognizes by some means that the signaling is associated with an - emergency call MUST add the emergency indication called for in A1a + emergency call MUST add the emergency indication called for in Id1 to the signaling before forwarding it. This marking mechanism must be different than QoS marking. Motivation: Marking ensures proper handling as an emergency call by downstream elements that may not recognize, for example, a - local variant of a logical emergency address (see requirement - A4+). + local variant of a logical emergency address. Id4. Emergency Identifier-based Marking: User agents, proxies, and other network elements that process signaling associated with emergency calls SHOULD be configured to recognize a reasonable - selection of logical emergency identifiers (described in - requirements below) as a means to initiate emergency marking. + selection of logical emergency identifiers as a means to initiate + emergency marking. Motivation: Since user devices roam, emergency identifiers may vary from region to region. It is therefore important that a network entity be able to perform mapping and/or call routing within the context of its own point of origin rather than relying on non-local logical emergency identifiers as the only basis for emergency marking of calls. Id5. Prevention of Fraud: A call identified as an emergency call or marked as such in accordance with the above requirements for @@ -529,20 +559,32 @@ of an enterprise). Motivation: Any signalling protocol requires the use of some identifier to indicate the called party, and the user terminal may lack the capability to determine the actual emergency address (PSAP uri). The use of local conventions may be required as a transition mechanism. Note: Such use complicates international movement of the user terminal, and evolution to a standardized universal emergency identifier or set of identifiers is preferred. + Id8. Universal Identifier Recognition: Universal identifier(s), MUST + be universally recognizable by any network element which supports + the ECRIT protocol." + + Id9. Universal Identifier not Recognized: A call MUST be recognized + as emergency call even if the specific emergency service requested + is not recognized." + + "Motivation: In order to have a robust system that supports + incremental Service deployment while still maintaining a fallback + capability." + 7. Mapping Protocol Given the requirement from the previous section, that of a single (or small number of) emergency identifier(s) which are independent of the caller's location, and since PSAPs only serve a limited geographic region, and for reasons of jurisdictional and local knowledge, having the call reach the appropriate PSAP based on a mapping protocol, is crucial. There are two basic architectures described for translating an @@ -610,37 +652,38 @@ limited caching mechanism should be supported. Ma4. Referral: The mapping client MUST be able to contact any server and be referred to another server that is more qualified to answer the query. Motivation: This requirement alleviates the potential for incorrect configurations to cause calls to fail, particularly for caller-based queries. - Ma5. The mapping protocol MUST allow a response to carry multiple - URIs. + Ma5. Multiple Response URIs: The mapping protocol response MUST + allow the return of multiple URIs. Motivation: In response to a mapping request, a server will normally provide a URI or set of URIs for contacting the appropriate PSAP. - Ma6. The mapping protocol MUST be able to return a URI or contact - method explicitly marked as an alternate contact. + Ma6. URI - Alternate Contact: The mapping protocol MUST be able to + return a URI or contact method explicitly marked as an alternate + contact. Motivation: In response to a mapping request, if an expected URI is unable to be returned, then mapping server may return an alternate URI. When and how this would be used will be described in an operational document. - Ma7. Multiple PSAP uri's: The mapping protocol MUST be able to - return multiple URLs for different PSAPs that cover the same area. + Ma7. Multiple PSAP URI's: The mapping protocol MUST be able to + return multiple URIs for different PSAPs that cover the same area. Ma8. URL properties: The mapping protocol must provide additional information that allows the querying entity to determine relevant properties of the URL. Motivation: In some cases, the same geographic area is served by several PSAPs, for example, a corporate campus might be served by both a corporate security department and the municipal PSAP. The mapping protocol should then return URLs for both, with information allowing the querying entity to choose one or the @@ -684,43 +727,54 @@ Ma14. Location Updates: It SHOULD be possible to have updates of location. Motivation: Updated location information may have an impact on PSAP routing. In some cases it may be possible to redirect that call to a more appropriate PSAP (some device measurement techniques provide quick (i.e. early), but imprecise "first fix" location). - Ma15. Extensible Protocol The mapping protocol MUST be extensible to - allow for the inclusion of new location fields. + Ma15. Extensible Protocol: The mapping protocol MUST be extensible + to allow for the inclusion of new location fields. Motivation: This is needed, for example, to accommodate future extensions to location information that might be included in the - PIDF-LO (I-D.ietf-geopriv-pidf-lo-03 [2]) + PIDF-LO (RFC 4119 [2]). Ma16. Split responsibility: The mapping protocol MUST allow that within a single level of the civic location hierarchy, multiple mapping servers handle subsets of the data elements. Motivation: For example, two directories for the same city or county may handle different streets within that city or county. - Ma17. The mapping function MUST be able to be invoked at any time, - including while an emergency call is in process. + Ma17. Pervasive Mapping: The mapping function MUST be able to be + invoked at any time, including while an emergency call is in + process. Ma18. Baseline query protocol: A mandatory-to-implement protocol MUST be specified. Motivation: An over-abundance of similarly-capable choices appears undesirable for interoperability. + Ma19. Single URI Scheme: The mapping protocol MAY return multiple + URIs, though it SHOULD return only one URI per scheme, so that + clients are not required to select among different targets for the + same contact protocol. + + Motivation: There may be two or more URIs returned when multiple + contact protocols are available (e.g. SIP and SMS). The client + may select among multiple contact protocols based on its + capabilities, preference settings, or availability. + 8. Security Considerations Note: Security Considerations are referenced in the ECRIT security document [3]. 9. Contributors The information contained in this document is a result of a joint effort based on individual contributions by those involved in the ECRIT WG. The contributors include Nadine Abbott, Hideki Arai, @@ -752,41 +806,44 @@ their input. 11. References 11.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Peterson, J., "A Presence-based GEOPRIV Location Object Format", - draft-ietf-geopriv-pidf-lo-03 (work in progress), - September 2004. + RFC 4119, December 2005. - [3] Tschofenig, H., "Security Threats and Requirements for Emergency - Calling", draft-tschofenig-ecrit-security-threats-01 (work in - progress), July 2005. + [3] Schulzrinne, H., "Security Threats and Requirements for + Emergency Calling", draft-taylor-ecrit-security-threats-01 (work + in progress), December 2005. + + [4] Schulzrinne, H., "A Uniform Resource Name (URN) for Services", + draft-schulzrinne-sipping-service-01 (work in progress), + October 2005. 11.2. Informative References - [4] Charlton, N., Gasson, M., Gybels, G., Spanner, M., and A. van + [5] 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. - [5] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. + [6] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J. Polk, "Geopriv Requirements", RFC 3693, February 2004. - [6] Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation", + [7] Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation", RFC 4103, June 2005. - [7] Wijk, A., "Framework of requirements for real-time text + [8] Wijk, A., "Framework of requirements for real-time text conversation using SIP", draft-ietf-sipping-toip-03 (work in progress), September 2005. Authors' Addresses Henning Schulzrinne Columbia University Department of Computer Science 450 Computer Science Building New York, NY 10027