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'9') (Obsoleted by RFC 3761) == Outdated reference: A later version (-03) exists of draft-ietf-sip-callee-caps-01 -- Obsolete informational reference (is this intentional?): RFC 2327 (ref. '11') (Obsoleted by RFC 4566) Summary: 4 errors (**), 0 flaws (~~), 7 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 ENUM WG J. Peterson 2 Internet-Draft NeuStar 3 Expires: May 26, 2004 November 26, 2003 5 enumservice registration for SIP Addresses-of-Record 6 draft-ietf-enum-sip-01 8 Status of this Memo 10 This document is an Internet-Draft and is in full conformance with 11 all provisions of Section 10 of RFC2026. 13 Internet-Drafts are working documents of the Internet Engineering 14 Task Force (IETF), its areas, and its working groups. Note that 15 other groups may also distribute working documents as Internet- 16 Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six months 19 and may be updated, replaced, or obsoleted by other documents at any 20 time. It is inappropriate to use Internet-Drafts as reference 21 material or to cite them other than as "work in progress." 23 The list of current Internet-Drafts can be accessed at http:// 24 www.ietf.org/ietf/1id-abstracts.txt. 26 The list of Internet-Draft Shadow Directories can be accessed at 27 http://www.ietf.org/shadow.html. 29 This Internet-Draft will expire on May 26, 2004. 31 Copyright Notice 33 Copyright (C) The Internet Society (2003). All Rights Reserved. 35 Abstract 37 This document registers an ENUM service for SIP (the Session 38 Initiation Protocol), pursuant to the guidelines in RFC2916bis. 39 Specifically, this document focuses on provisioning SIP addresses-of- 40 record in ENUM. 42 Table of Contents 44 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3 45 2. ENUM Service Registration . . . . . . . . . . . . . . . . . . . 3 46 3. Addresses-of-record in SIP . . . . . . . . . . . . . . . . . . . 4 47 4. The 'E2U+SIP' enumservice . . . . . . . . . . . . . . . . . . . 6 48 5. Example of E2U+SIP enumservice . . . . . . . . . . . . . . . . . 6 49 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 50 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 51 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 52 Normative References . . . . . . . . . . . . . . . . . . . . . . 7 53 Informative References . . . . . . . . . . . . . . . . . . . . . 7 54 A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8 55 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 9 57 1. Introduction 59 ENUM (E.164 Number Mapping, RFC2916 [9]) is a system that uses DNS 60 (Domain Name Service, RFC1034 [3]) to translate telephone numbers, 61 like '+12025332600', into URIs (Uniform Resource Identifiers, RFC2396 62 [4]), like 'sip:egar@example.com'. ENUM exists primarily to 63 facilitate the interconnection of systems that rely on telephone 64 numbers with those that use URIs to route transactions. ENUM is 65 currently under revision in RFC2916bis [1]; this document applies to 66 the revised version of ENUM described in the work-in-progress. 68 SIP (Session Initiation Protocol, RFC3261 [2]) is a text-based 69 application protocol that allows endpoints on the Internet to 70 discover one another in order to exchange context information about a 71 session they would like to share. Common forms of communication that 72 are set up by SIP include Internet telephony, instant messaging, 73 video, Internet gaming and other forms of real-time communications. 74 SIP is a multi-service protocol capable of initiating sessions 75 involving different forms of real-time communications simultaneously. 76 SIP is a protocol that finds the best way for parties to communicate. 78 2. ENUM Service Registration 80 As defined in [1], the following is a template covering information 81 needed for the registration of the enumservice specified in this 82 document. 84 Enumservice Name: "E2U+SIP" 86 Type(s): "SIP" 88 Subtype(s): N/A 90 URI Scheme(s): "sip:", "sips:" 92 Functional Specification: see Section 4 94 Security considerations: see Section 6 96 Intended usage: COMMON 98 Author: Jon Peterson (jon.peterson@neustar.biz) 100 Any other information that the author deems interesting: See 101 Section 3 103 3. Addresses-of-record in SIP 105 This document specifies an enumservice field that is appropriate for 106 SIP addresses-of-record URIs. Various other types of URIs can be 107 present in SIP requests. A URI that is associated with a particular 108 SIP user agent (for example, a SIP phone) is commonly known as a SIP 109 contact address. 111 The difference between a contact address and an address-of-record is 112 like the difference between a device and its user. While there is no 113 formal distinction in the syntax of these two forms of addresses, 114 contact addresses are associated with a particular device, and may 115 have a very device-specific form (like sip:10.0.0.1, or 116 sip:edgar@ua21.example.com). An address-of-record, however, 117 represents a identity of the user, generally a long-term identity, 118 and it does not have a dependency on any device; users can move 119 between devices or even be associated with multiple devices at one 120 time while retaining the same address-of-record. A simple URI, 121 generally of the form 'sip:egdar@example.com', is used for an 122 address-of-record. 124 When a SIP request is created by a user agent, it populates the 125 address-of-record of its target in its To header field and 126 (generally) Request-URI. The address-of-record of the user that is 127 sending the request populates the From header field of the message; 128 the contact address of the device from which the request is sent is 129 listed in the Contact header field. 131 By sending a registration to a registrar on behalf of its user, a SIP 132 device (i.e. a user agent) can temporarily associate its own contact 133 address with the user's address-of-record. In so doing, the device 134 becomes eligible to receive requests that are sent to the address-of- 135 record. Upon receiving the registration request, the registrar 136 modifies the provisioning data in a SIP location service to create a 137 mapping between the address-of-record for the user and the device 138 where the user can currently be reached. When future requests arrive 139 at the administrative domain of this location service for the user in 140 question, proxy servers ask the location service where to find the 141 user, and will in turn discover the registered contact address(es). 142 A SIP-based follow-me telephony service, for example, would rely on 143 this real-time availability data in order to find the best place to 144 reach the end user without having to cycle through numerous devices 145 from which the user is not currently registered. Note that 146 addresses-of-record can be registered with other addresses-of-record; 147 for example, while at home, a user might elect to register the 148 address-of-record they use as their personal identity under their 149 work address-of-record in order to direct requests for their work 150 identity to whatever devices they might have associated with their 151 home address-of-record. 153 When a SIP entity (be it a user agent or proxy server) needs to make 154 a forwarding decision for a Request-URI containing an address-of- 155 record, it uses the mechanisms described in the SIP specification 156 (RFC3263) to locate the proper resource in the network. Ordinarily, 157 this entails resolving the domain portion of the URI (example.com in 158 the example above) in order to route the call to a proxy server that 159 is responsible for that domain. 161 SIP user agents have specific communications capabilities (such as 162 the ability to initiate voice communications with particular codecs, 163 or support for particular SIP protocol extensions). Because an 164 address-of-record does not represent any particular device or set of 165 devices, an address-of-record does not have capabilities as such. 166 When a SIP user agent sends a request to an address-of-record, it 167 begins a phase of capability negotiation that will eventually 168 discover the best way for the originator to communicate with the 169 target. The originating user agent first expresses capabilities of 170 its own in the request it sends (and preferences for the type of 171 session it would like to initiate). The expression of these 172 capabilities may entail the usage of SDP [11] to list acceptable 173 types of media supported and favored by the client, the inclusion of 174 Required/Supported headers to negotiate compatibility of extensions, 175 and possibly the usage of optional SIP extensions, for example using 176 callee capabilities [10] to communicate request handling 177 dispositions. Proxy servers or endpoints subsequently return 178 responses that allow a rich bidirectional capability negotiation 179 process. 181 The process by which SIP endpoints negotiate capabilities can overlap 182 with the primary service provided by NAPTR records: permitting the 183 originating client to select a particular URI for communications 184 based on an ordered list of enumservices. However, ENUM's capability 185 management mechanism is decidedly one-way - the administrator of the 186 telephone number expresses capabilities (in the form of protocol 187 names) and preferences that the client must evaluate without 188 negotiation. Moreover, listing available protocols is not comparable 189 to agreement on session media (down to the codec/interval level) and 190 protocol extension support - it would be difficult to express, in the 191 level of detail necessary to arrange a desired session, the 192 capabilities of a SIP device within a NAPTR service field. 193 Provisioning contact addresses in ENUM rather than addresses-of- 194 record would compromise the SIP capability negotiation and discovery 195 process. Much of the benefit of using a URI comes from the fact that 196 it represents a logical service associated with a user, rather than a 197 device - indeed, if ENUM wished to target particular devices, 198 'E2IPv4' would be a more appropriate resolution service to define 199 than 'E2U'. 201 SIP addresses-of-record may use the SIP URI scheme or the SIPS URI 202 scheme. The SIPS URI scheme, when used in an address-of-record, 203 indicates that the user it represents can only be reached over a 204 secure connection (using TLS). 206 4. The 'E2U+SIP' enumservice 208 Traditionally, the services field of a NAPTR record (as defined in 209 [6]) contains a string that is composed of two subfields: a 210 'protocol' subfield and a 'resolution service' subfield. ENUM in 211 particular defines an 'E2U' (E.164 to URI) resolution service. This 212 document defines an 'E2U+SIP' enumservice for SIP. 214 The scheme of the URI that will appear in the regexp field of a NAPTR 215 record using the 'E2U+SIP' enumservice may either be 'SIP' or 'SIPS'. 216 This enumservice is best suited to SIP addresses-of-record. 218 When a SIP address-of-record appears in the regexp field of a NAPTR 219 record, there is no need to further qualify the enumservice field 220 with any capability data, since addresses-of-record do not have 221 capabilities. 223 There is also generally no need to have more than one NAPTR record 224 under a single telephone number that points to a SIP address-of- 225 record. 227 Note that the user portion of a SIP URI may contain a telephone 228 number (e.g. 'sip:+1442079460148@example.com'). Clients should be 229 careful to avoid infinite loops when recursively performing ENUM 230 queries on URIs that result from an ENUM lookup. 232 5. Example of E2U+SIP enumservice 234 The following is an example of the use of the enumservice registered 235 by this document in a NAPTR resource record. 237 $ORIGIN 8.4.1.0.6.4.9.7.0.2.4.4.e164.arpa. 238 IN NAPTR 10 100 "u" "E2U+sip" "!^.*$!sip:edgar@example.com!" . 240 6. Security Considerations 242 A SIP address-of-record is a canonical address by which a user is 243 known - placing this address in ENUM is comparable to placing an 244 email address or a similar URI in the DNS. 246 DNS does not make policy decisions about the records that it shares 247 with an inquirer. All DNS records must be assumed to be available to 248 all inquirers at all times. The information provided within an ENUM 249 record set must therefore be considered to be open to the public - 250 which is a cause for some privacy considerations. 252 Unlike a traditional telephone number, the resource identified by a 253 SIP URI may require that callers provide cryptographic credentials 254 for authentication and authorization before a user is alerted. In 255 this respect, ENUM in concert with SIP can actually provide far 256 greater protection from unwanted callers than the existing PSTN, 257 despite the public availability of ENUM records. 259 7. IANA Considerations 261 This document registers the 'E2U+SIP' enumservice under the 262 enumservice registry described in the IANA considerations in 263 RFC2916bis. Details of the registration are given in Section 2. 265 Normative References 267 [1] Faltstrom, P. and M. Mealling, "The E.164 to URI DDDS 268 Application", draft-ietf-enum-rfc2916bis-03 (work in progress), 269 January 2003. 271 [2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 272 Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: 273 Session Initiation Protocol", RFC 3261, May 2002. 275 [3] Mockapetris, P., "Domain Names - Concepts and Facilities", RFC 276 1034, November 1987. 278 [4] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource 279 Identifiers (URI): Generic Syntax", RFC 2396, August 1998. 281 [5] Vaha-Sipila, A., "URLs for Telephone Calls", RFC 2806, April 282 2000. 284 [6] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part 285 Three: The Domain Name System (DNS) Database", RFC 3403, October 286 2002. 288 Informative References 290 [7] International Telecommunications Union, "Recommendation E.164: 291 The international public telecommunication numbering plan", May 292 1997, . 294 [8] Mealling, M. and R. Daniel, "The Naming Authority Pointer 295 (NAPTR) DNS Resource Record", RFC 2915, September 2000. 297 [9] Faltstrom, P., "E.164 number and DNS", RFC 2916, September 298 2000. 300 [10] Rosenberg, J., Schulzrinne, H. and P. Kyzviat, "Indicating User 301 Agent Capabilities in the Session Initiation Protocol (SIP)", 302 draft-ietf-sip-callee-caps-01 (work in progress), October 2003. 304 [11] Handley, M. and V. Jacobson, "SDP: Session Description 305 Protocol", RFC 2327, April 1998. 307 Author's Address 309 Jon Peterson 310 NeuStar, Inc. 311 1800 Sutter St 312 Suite 570 313 Concord, CA 94520 314 USA 316 Phone: +1 925/363-8720 317 EMail: jon.peterson@neustar.biz 318 URI: http://www.neustar.biz/ 320 Appendix A. Acknowledgments 322 Thanks to Richard Shockey for comments on the initial draft of this 323 document, and to Allison Mankin for valuable review comments. 325 Full Copyright Statement 327 Copyright (C) The Internet Society (2003). 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