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Crocker 3 Internet-Draft Brandenburg 4 Expires: June 6, 2003 J. Peterson 5 NeuStar 6 December 6, 2002 8 Common Profile: Instant Messaging 9 draft-ietf-impp-im-01 11 Status of this Memo 13 This document is an Internet-Draft and is in full conformance with 14 all provisions of Section 10 of RFC2026. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at http:// 27 www.ietf.org/ietf/1id-abstracts.txt. 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 This Internet-Draft will expire on June 6, 2003. 34 Copyright Notice 36 Copyright (C) The Internet Society (2002). All Rights Reserved. 38 Abstract 40 Instant messaging is defined in RFC2778 [5]. Today, numerous instant 41 messaging protocols are in use, and little interoperability between 42 services based on these protocols has been achieved. This 43 specification defines common semantics and data formats for instant 44 messaging to facilitate the creation of gateways between instant 45 messaging services. 47 Table of Contents 49 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 50 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 51 3. Abstract Instant Messaging Service . . . . . . . . . . . . . 4 52 3.1 Overview of Instant Messaging Service . . . . . . . . . . . 4 53 3.2 Identification of INSTANT INBOXes . . . . . . . . . . . . . 5 54 3.2.1 Address Resolution . . . . . . . . . . . . . . . . . . . . . 5 55 3.3 Format of Instant Messages . . . . . . . . . . . . . . . . . 5 56 3.4 The Messaging Service . . . . . . . . . . . . . . . . . . . 5 57 3.4.1 The Message Operation . . . . . . . . . . . . . . . . . . . 5 58 3.4.2 Looping . . . . . . . . . . . . . . . . . . . . . . . . . . 6 59 4. Security Considerations . . . . . . . . . . . . . . . . . . 7 60 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7 61 5.1 The IM URI Scheme . . . . . . . . . . . . . . . . . . . . . 7 62 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 63 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 8 64 A. IM URI IANA Registration Template . . . . . . . . . . . . . 9 65 A.1 URI scheme name . . . . . . . . . . . . . . . . . . . . . . 9 66 A.2 URI scheme syntax . . . . . . . . . . . . . . . . . . . . . 9 67 A.3 Character encoding considerations . . . . . . . . . . . . . 9 68 A.4 Intended usage . . . . . . . . . . . . . . . . . . . . . . . 9 69 A.5 Applications and/or protocols which use this URI scheme 70 name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 71 A.6 Interoperability considerations . . . . . . . . . . . . . . 10 72 A.7 Security considerations . . . . . . . . . . . . . . . . . . 10 73 A.8 Relevant publications . . . . . . . . . . . . . . . . . . . 10 74 A.9 Person & email address to contact for further information . 10 75 A.10 Author/Change controller . . . . . . . . . . . . . . . . . . 10 76 A.11 Applications and/or protocols which use this URI scheme 77 name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 78 B. Issues of Interest . . . . . . . . . . . . . . . . . . . . . 10 79 B.1 Address Mapping . . . . . . . . . . . . . . . . . . . . . . 10 80 B.2 Source-Route Mapping . . . . . . . . . . . . . . . . . . . . 11 81 Normative References . . . . . . . . . . . . . . . . . . . . 8 82 C. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 11 83 Full Copyright Statement . . . . . . . . . . . . . . . . . . 12 85 1. Introduction 87 Instant messaging is defined in RFC2778 [5]. Today, numerous instant 88 messaging protocols are in use, and little interoperability between 89 services based on these protocols has been achieved. This 90 specification defines semantics and data formats for common services 91 of Instant Messaging to facilitate the creation of gateways between 92 instant messaging services. 94 Service behavior is described abstractly in terms of operations 95 invoked between the consumer and provider of a service. Accordingly, 96 each IM service must specify how this behavior is mapped onto its own 97 protocol interactions. The choice of strategy is a local matter, 98 providing that there is a clear relation between the abstract 99 behaviors of the service (as specified in this memo) and how it is 100 faithfully realized by a particular instant messaging service. 102 The attributes for each operation are defined using an abstract 103 syntax. Although the syntax specifies the range of possible data 104 values, each IM service must specify how well-formed instances of the 105 abstract representation are encoded as a concrete series of bits. 107 For example, one strategy might transmit an instant message as 108 textual key/value pairs, another might use a compact binary 109 representation, and a third might use nested containers. The choice 110 of strategy is a local matter, providing that there is a clear 111 relation between the abstract syntax (as specified in this memo) and 112 how it is faithfully encoded by an particular instant messaging 113 service. 115 In order to provide a means for the preservation of end-to-end 116 features (especially security) to pass through instant messaging 117 interoperability gateways, this specification also provides 118 recommendations for instant messaging document formats that could be 119 employed by instant messaging protocols. 121 2. Terminology 123 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 124 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT 125 RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as 126 described in RFC2119 [1] and indicate requirement levels for 127 compliant implementations. 129 This memos makes use of the vocabulary defined in RFC2778 [5]. Terms 130 such as CLOSED, INSTANT INBOX, INSTANT MESSAGE, and OPEN are used in 131 the same meaning as defined therein. 133 This document defines operations and attributes of an instant 134 messaging service. In order for a protocol to interface with an 135 instant messaging gateway, it must support all of the operations 136 described in this document (i.e. the instant messaging protocol must 137 have some message or capability that provides the function described 138 by this operation). Similarly, the attributes defined for these 139 operations must correspond to information available in the instant 140 messaging protocol in order for the protocol to interface with 141 gateways defined by this specification. Note that these attributes 142 provide only the minimum possible information that needs to be 143 specified for interoperability - the functions in an instant 144 messaging protocol that correspond to the operations described in 145 this document can contain additional information that will not be 146 mapped by CPIM. 148 3. Abstract Instant Messaging Service 150 3.1 Overview of Instant Messaging Service 152 When an application wants to send a message to an INSTANT INBOX, it 153 invokes the message operation, e.g., 155 +-------+ +-------+ 156 | | | | 157 | appl. | -- message ------> | IM | 158 | | | svc. | 159 +-------+ +-------+ 161 The message operation has the following attributes: source, 162 destination, MaxForwards and TransID. 'source' and 'destination' 163 identity the originator and destination of an instant message, 164 respectively, and consist of an INSTANT INBOX identifier (as 165 described in Section 3.2). The MaxForwards is a hop counter used in 166 order to avoid loops through gateways. The TransID is a unique 167 identifier used to correlate message operations to response 168 operations. 170 The message operation also has some content, the instant message 171 itself, which may be textual, or which may consist of other data. 172 Some further information on content is provided in Section 3.3. 174 Upon receiving a message operation, the service immediately responds 175 by invoking the response operation containing the same transaction- 176 identifier, e.g., 177 +-------+ +-------+ 178 | | | | 179 | appl. | <----- response -- | IM | 180 | | | svc. | 181 +-------+ +-------+ 183 The response operation contains the following attributes: TransID and 184 status. The TransID is used to correlate the response to a 185 particular instant message. Status indicates whether the delivery of 186 the message succeeded or failed. 188 3.2 Identification of INSTANT INBOXes 190 An INSTANT INBOX is specified using an instant messaging URI with the 191 'im:' URI scheme. The full syntax of the IM URI scheme is given in 192 Appendix A. An example would be: "im:fred@example.com" 194 3.2.1 Address Resolution 196 A client determines the address of an appropriate system running a 197 server by resolving the destination domain name that is part of the 198 identifier to either an intermediate relay system or a final target 199 system. 201 Compliant implementations SHOULD follow the guidelines for 202 dereferencing URIs given in [2]. 204 3.3 Format of Instant Messages 206 This specification defines an abstract interoperability mechanism for 207 instant messaging protocols; the message content definition given 208 here pertains to semantics rather than syntax. However, some 209 important properties for interoperability can only be provided if a 210 common end-to-end format for instant messaging is employed by the 211 interoperating instant messaging protocols. Implementations 212 therefore SHOULD support the format defined in MSGFMT [4]. 214 3.4 The Messaging Service 216 Note that the transaction-identifier parameters used with the instant 217 messaging service are potentially long-lived. Accordingly, the 218 values generated for this parameter should be unique across a 219 significant duration of time. 221 3.4.1 The Message Operation 223 When an application wants to send an INSTANT MESSAGE, it invokes the 224 message operation. 226 When the service is informed of the message operation, it performs 227 these steps: 229 1. If the source or destination does not refer to a valid INSTANT 230 INBOX, a response operation having status "failure" is invoked. 232 2. If access control does not permit the application to request this 233 operation, a response operation having status "failure" is 234 invoked. 236 3. Otherwise: 238 If the service is able to successfully deliver the message, a 239 response operation having status "success" is invoked. 241 If the service is unable to successfully deliver the message, 242 a response operation having status "failure" is invoked. 244 If the service must delegate responsibility for delivery, and 245 if the delegation will not result in a future authoritative 246 indication to the service, a response operation having status 247 "indeterminant" is invoked. 249 If the service must delegate responsibility for delivery, and 250 if the delegation will result in a future authoritative 251 indication to the service, then a response operation is 252 invoked immediately after the indication is received. 254 When the service invokes the response operation, the transID 255 parameter is identical to the value found in the message operation 256 invoked by the application. 258 3.4.2 Looping 260 The dynamic routing of instant messages can result in looping of a 261 message through a relay. Detection of loops is not always obvious, 262 since aliasing and group list expansions can legitimately cause a 263 message to pass through a relay more than one time. 265 This document assumes that instant messaging protocols that can be 266 gatewayed by CPIM support some semantic equivalent to an integer 267 value that indicates the maximum number of hops through which a 268 message can pass. When that number of hops has been reached, the 269 message is assumed to have looped. 271 When a CPIM gateway relays an instant message, it decrements the 272 value of the MaxForwards attribute. This document does not mandate 273 any particular initial setting for the MaxForwards element in instant 274 messaging protocols, but it is recommended that the value be 275 reasonably large (over one hundred). 277 If a CPIM gateway handles an instant message operation that has a 278 MaxForwards attribute of 0, it discards the message and invokes a 279 failure operation. 281 4. Security Considerations 283 Detailed security considerations for instant messaging protocols are 284 given in RFC2779 (in particular, requirements are given in section 285 5.4 and some motivating discussion in 8.1). 287 CPIM defines an interoperability function that is employed by 288 gateways between instant messaging protocols. CPIM gateways MUST be 289 compliant with the minimum security requirements of the instant 290 messaging protocols with which they interface. 292 Note that end-to-end security properties (especially confidentiality 293 and integrity) between instant messaging user agents that interface 294 through a CPIM gateway can only be provided if a common instant 295 message format (such as the format described in MSGFMT [4]) is 296 supported by the protocols interfacing with the CPIM gateway. 298 5. IANA Considerations 300 The IANA assigns the "im" scheme. 302 5.1 The IM URI Scheme 304 The Instant Messaging (IM) URI scheme designates an Internet 305 resource, namely an INSTANT INBOX. 307 The syntax of an IM URI is given in Appendix A. 309 6. Contributors 311 The following individuals made substantial textual contributions to 312 this document: 314 Athanassios Diacakis (thanos.diacakis@openwave.com) 316 Florencio Mazzoldi (flo@networkprojects.com) 318 Christian Huitema (huitema@microsoft.com) 319 Graham Klyne (gk@ninebynine.org) 321 Jonathan Rosenberg (jdrosen@dynamicsoft.com) 323 Robert Sparks (rsparks@dynamicsoft.com) 325 Hiroyasu Sugano (suga@flab.fujitsu.co.jp) 327 Normative References 329 [1] Bradner, S., "Key words for use in RFCs to indicate requirement 330 levels", RFC 2119, March 1997. 332 [2] Crocker, D. and J. Peterson, "Address resolution for Instant 333 Messaging and Presence", draft-ietf-impp-srv-00 (work in 334 progress), October 2002. 336 [3] Resnick, P., "Internet Message Format", RFC 2822, STD 11, April 337 2001. 339 [4] Atkins, D. and G. Klyne, "Common Presence and Instant Messaging: 340 Message Format", draft-ietf-impp-cpim-msgfmt-05 (work in 341 progress), December 2001. 343 [5] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and 344 Instant Messaging", RFC 2778, February 2000. 346 [6] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging / 347 Presence Protocol Requirements", RFC 2779, February 2000. 349 [7] Allocchio, C., "GSTN Address Element Extensions in Email 350 Services", RFC 2846, June 2000. 352 Authors' Addresses 354 Dave Crocker 355 Brandenburg InternetWorking 356 675 Spruce Drive 357 Sunnyvale, CA 94086 358 US 360 Phone: +1 408/246-8253 361 EMail: dcrocker@brandenburg.com 362 Jon Peterson 363 NeuStar, Inc. 364 1800 Sutter St 365 Suite 570 366 Concord, CA 94520 367 US 369 Phone: +1 925/363-8720 370 EMail: jon.peterson@neustar.biz 372 Appendix A. IM URI IANA Registration Template 374 This section provides the information to register the im: instant 375 messaging URI. 377 A.1 URI scheme name 379 im 381 A.2 URI scheme syntax 383 The syntax follows the existing mailto: URI syntax specified in 384 RFC2368. The ABNF is: 386 IM-URI = "im:" [ to ] [ headers ] 387 to = #mailbox 388 headers = "?" header *( "&" header ) 389 header = hname "=" hvalue 390 hname = *urlc 391 hvalue = *urlc 393 A.3 Character encoding considerations 395 Representation of non-ASCII character sets in local-part strings is 396 limited to the standard methods provided as extensions to RFC2822 397 [3]. 399 A.4 Intended usage 401 Use of the im: URI follows closely usage of the mailto: URI. That 402 is, invocation of an IM URI will cause the user's instant messaging 403 application to start, with destination address and message headers 404 fill-in according to the information supplied in the URI. 406 A.5 Applications and/or protocols which use this URI scheme name 408 It is anticipated that protocols compliant with RFC2779, and meeting 409 the interoperability requirements specified here, will make use of 410 this URI scheme name. 412 A.6 Interoperability considerations 414 The underlying exchange protocol used to send an instant message may 415 vary from service to service. Therefore complete, Internet-scale 416 interoperability cannot be guaranteed. However, a service conforming 417 to this specification permits gateways to achieve interoperability 418 sufficient to the requirements of RFC2779. 420 A.7 Security considerations 422 When IM URIs are placed in instant messaging protocols, they convey 423 the identity of the sender and/or the recipient. In some cases, 424 anonymous messaging may be desired. Such a capability is beyond the 425 scope of this specification. 427 A.8 Relevant publications 429 RFC2779, RFC2778 431 A.9 Person & email address to contact for further information 433 Jon Peterson [mailto:jon.peterson@neustar.biz] 435 A.10 Author/Change controller 437 This scheme is registered under the IETF tree. As such, IETF 438 maintains change control. 440 A.11 Applications and/or protocols which use this URI scheme name 442 Instant messaging service 444 Appendix B. Issues of Interest 446 This appendix briefly discusses issues that may be of interest when 447 designing an interoperation gateway. 449 B.1 Address Mapping 451 When mapping the service described in this memo, mappings that place 452 special information into the im: address local-part MUST use the 453 meta-syntax defined in RFC2846 [7]. 455 B.2 Source-Route Mapping 457 The easiest mapping technique is a form of source- routing and 458 usually is the least friendly to humans having to type the string. 459 Source-routing also has a history of operational problems. 461 Use of source-routing for exchanges between different services is by 462 a transformation that places the entire, original address string into 463 the im: address local part and names the gateway in the domain part. 465 For example, if the destination INSTANT INBOX is "pepp://example.com/ 466 fred", then, after performing the necessary character conversions, 467 the resulting mapping is: 469 im:pepp=example.com/fred@relay-domain 471 where "relay-domain" is derived from local configuration information. 473 Experience shows that it is vastly preferable to hide this mapping 474 from end-users - if possible, the underlying software should perform 475 the mapping automatically. 477 Appendix C. Acknowledgments 479 The authors would like to acknowledge John Ramsdell for his comments, 480 suggestions and enthusiasm. Thanks to Derek Atkins for editorial 481 fixes. 483 Full Copyright Statement 485 Copyright (C) The Internet Society (2002). All Rights Reserved. 487 This document and translations of it may be copied and furnished to 488 others, and derivative works that comment on or otherwise explain it 489 or assist in its implementation may be prepared, copied, published 490 and distributed, in whole or in part, without restriction of any 491 kind, provided that the above copyright notice and this paragraph are 492 included on all such copies and derivative works. However, this 493 document itself may not be modified in any way, such as by removing 494 the copyright notice or references to the Internet Society or other 495 Internet organizations, except as needed for the purpose of 496 developing Internet standards in which case the procedures for 497 copyrights defined in the Internet Standards process must be 498 followed, or as required to translate it into languages other than 499 English. 501 The limited permissions granted above are perpetual and will not be 502 revoked by the Internet Society or its successors or assigns. 504 This document and the information contained herein is provided on an 505 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 506 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 507 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 508 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 509 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 511 Acknowledgement 513 Funding for the RFC Editor function is currently provided by the 514 Internet Society.