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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SIMPLE J. Rosenberg 3 Internet-Draft S. Donovan 4 Intended status: Standards Track K. McMurry 5 Expires: May 15, 2008 Cisco 6 November 12, 2007 8 Optimizing Federated Presence with View Sharing 9 draft-rosenberg-simple-view-sharing-00 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on May 15, 2008. 36 Copyright Notice 38 Copyright (C) The IETF Trust (2007). 40 Abstract 42 Presence federation refers to the exchange of presence information 43 between systems. One of the primary challenges in presence 44 federation is scale. With a large number of watchers in one domain 45 obtaining presence for many presentities in another, the amount of 46 notification traffic is large. This document describes an extension 47 to the Session Initiation Protocol (SIP) event framework, called view 48 sharing. View sharing can substantially reduce the amount of 49 traffic, but requires a certain level of trust between domains. View 50 sharing allows the amount of presence traffic between domains to 51 achieve the theoretical lower bound on information exchange in any 52 presence system. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Overview of Operation . . . . . . . . . . . . . . . . . . . . 4 58 3. RLS Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 7 59 3.1. On Receipt of a Resource List Subscription Request . . . . 7 60 3.1.1. Authentication and Authorization . . . . . . . . . . . 7 61 3.1.2. No Active Back-End Subscription . . . . . . . . . . . 7 62 3.1.3. Active Back-End Subscription . . . . . . . . . . . . . 8 63 3.2. Processing NOTIFY Requests . . . . . . . . . . . . . . . . 9 64 3.2.1. Processing ACL-Infos . . . . . . . . . . . . . . . . . 9 65 3.2.2. Processing Presence Documents . . . . . . . . . . . . 10 66 3.2.3. Processing Back-End Terminations . . . . . . . . . . . 11 67 4. Presence Agent Behavior . . . . . . . . . . . . . . . . . . . 11 68 4.1. Authentication and Authorization . . . . . . . . . . . . . 11 69 4.2. Processing Initial SUBSCRIBE Requests . . . . . . . . . . 12 70 4.3. SUBSCRIBE Refreshes . . . . . . . . . . . . . . . . . . . 12 71 4.4. Policy Changes . . . . . . . . . . . . . . . . . . . . . . 13 72 4.5. Presence State Changes . . . . . . . . . . . . . . . . . . 14 73 5. ACL Format . . . . . . . . . . . . . . . . . . . . . . . . . . 14 74 5.1. Document Structure and Semantics . . . . . . . . . . . . . 15 75 5.2. Trust Considerations when Construcing ACLs . . . . . . . . 16 76 5.3. Example Documents . . . . . . . . . . . . . . . . . . . . 17 77 5.4. Rule Determination Algorithm . . . . . . . . . . . . . . . 18 78 5.5. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . 20 79 6. Performance Analysis . . . . . . . . . . . . . . . . . . . . . 20 80 7. Requirements Analysis . . . . . . . . . . . . . . . . . . . . 21 81 8. Security Considerations . . . . . . . . . . . . . . . . . . . 23 82 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 83 9.1. MIME Type Registration . . . . . . . . . . . . . . . . . . 24 84 9.2. URN Sub-Namespace Registration . . . . . . . . . . . . . . 25 85 9.3. Schema Registration . . . . . . . . . . . . . . . . . . . 26 86 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 87 10.1. Normative References . . . . . . . . . . . . . . . . . . . 26 88 10.2. Informative References . . . . . . . . . . . . . . . . . . 27 89 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28 90 Intellectual Property and Copyright Statements . . . . . . . . . . 29 92 1. Introduction 94 Presence refers to the ability, willingness and desire to communicate 95 across differing devices, mediums and services [RFC2778]. Presence 96 is described using presence documents [RFC3863] [RFC4479], exchanged 97 using a SIP-based event package [RFC3856]. 99 Presence federation refers to the interconnection of disparate 100 systems for the purposes of sharing presence information. This 101 interconnection involves passing of subscriptions from one system to 102 another, and then the passing of notifications in the opposite 103 direction. 105 [I-D.ietf-simple-interdomain-scaling-analysis] has analyzed the 106 amount of traffic, in terms of messages and in terms of bytes, which 107 flow between systems in various federated use cases. These numbers 108 demonstrate that presence traffic can be a substantial source of 109 overhead. The root cause of this scale challenge is the so-called 110 multiplicative effect of presence data. If there are N users, each 111 of which have B buddies on their buddy list, and each buddy changes 112 state L times per hour, the amount of notification traffic is 113 proportional to N*B*L. For example, in the case of two extremely 114 large public IM providers that federate with each other (each with 20 115 million users), [I-D.ietf-simple-interdomain-scaling-analysis] shows 116 that the amount of traffic due to these steady state notifications is 117 18.4 billion messages per day, an astoundingly large number. 118 Overhead for subscription maintenance and refreshes brings the total 119 to 25.6 billion per day. 121 The overhead for SIP-based presence can be reduced using SIP 122 optimizations. In particular, [I-D.ietf-sip-subnot-etags] can reduce 123 the amount of traffic due to refreshes and polls. However, this 124 optimization targets the overhead, and doesn't address the core 125 scaling problem - the multiplicative effect of presence data. 127 For this reason, there is a clear need to improve the scale of SIMPLE 128 in federated envrionments. 129 [I-D.houri-sipping-presence-scaling-requirements] has laid out a set 130 of requirements for optimizations. The essence of these requirements 131 are that the extension should improve performance, while being 132 backwards compatible and supporting the privacy and policy 133 requirements of users. 135 This document defines a mechanism called view sharing in support of 136 those requirements. The key idea with view sharing is that when 137 there are many watchers in a domain to a single presentity in another 138 domain, each of which is actually going to get the exact same 139 presence document, the domain of the watchers extends a single 140 subscription to the domain of the presentity, and the domain of the 141 presentity sends a single copy of the presence document back to the 142 domain of the watcher. Assuming a symmetrical system whereby the 143 average buddies per watcher is B and the average number of watchers 144 for a user is also B, this optimization can reduce the overall 145 subscription overhead and notification traffic by a factor of B. 147 2. Overview of Operation 149 The extensions works in the environment shown in Figure 1. The 150 environment assumes two domains. There are some number of watchers 151 (W1 - W3) in the domain on the left, which we call the watching 152 domain. All of those watchers are interested in the presence of a 153 single presentity P1 in the domain on the right, which we call the 154 serving domain. The watchers all make use of a resource list server 155 (RLS) [RFC4662] which stores their buddy lists and performs the buddy 156 list expansion. Consequently, when each watcher subscribes to their 157 buddy list on the RLS, in absence of any optimizations, the RLS will 158 generate three separate subscriptions to P1, each of which reaches 159 the presence server in the serving domain. 161 . 162 +--------------+ . +--------------+ 163 | | . | | 164 | | SUB . | | 165 | | -------.---> | Presence | 166 | RLS | NOT . | Server | 167 | | <------.---- | | 168 | | . | | 169 | | . | | 170 +--------------+ . +--------------+ 171 ^ ^ ^ . ^ 172 List | | | . | PUB 173 SUB | | | . | 174 | | | . | 175 +----+ +----+ +----+ . +----+ 176 | | | | | | . | | 177 | W1 | | W2 | | W3 | . | P1 | 178 | | | | | | . | | 179 +----+ +----+ +----+ . +----+ 180 . 181 . 182 . 183 Watching . Serving 184 Domain . Domain 185 . 187 Figure 1: Deployment Model 189 Of course, in practice each domain will act as both a watching domain 190 and a serving domain, thus implementing both sides of the system. 192 The initial SUBSCRIBE generated by the RLS includes a SIP option tag 193 "view-share" in the Supported header field, indicating that the RLS 194 supports the view sharing extension. If the presence server also 195 supports the extension, it makes use of it and includes an indication 196 of this fact in the Require header field in the SUBSCRIBE response 197 and in NOTIFY requests it generates. 199 View sharing requires a level of trust between the two domains. 200 Consequently, the connection between them utilizes TLS with mutual 201 authentication. The presence server verifies that the certificate 202 presented in the mutual authentication matches the domain of the 203 watcher. 205 If this is the first subscription from domain 1 for that particular 206 presentity, the presence server accepts the subscription (assuming 207 the watcher is authorized of course). The notifications sent to the 208 RLS include two separate pieces of state. One is the actual presence 209 state for the presentity. The other is an Access Control List (ACL) 210 document. This document describes the set of other watchers from the 211 originating domain, if any, who are authorized to see exactly the 212 same presence document - in other words, the set of users that share 213 the same view. Should one of those watchers seek the presence of 214 that presentity, the RLS from the originating domain does not need to 215 generate a back-end subscription; rather, it just uses the presence 216 document it is receiving from the original subscription, and passes 217 it to both watchers. The ACL can also list users in the originating 218 domain that are authorized to subscribe to that presentity, but who 219 will end up receiving a different view. Should one of those watchers 220 subscribe, the RLS knows that it must perform a back-end subscription 221 to obtain that view. The ACL can also list watchers in the 222 originating domain that are not authorized at all, in which case the 223 RLS could immediately reject their subscriptions. Finally, if the 224 ACL says nothing about a particular watcher, it means that the 225 presence server has elected to say nothing about what view this 226 watcher will receive. Consequently, the RLS must perform a back-end 227 subscription should that watcher subscribe to the presentity. 229 Other subsequent subscriptions to the same presentity from the same 230 originating domain are processed in a similar way. However, the 231 presence server in the serving domain will keep track of the set of 232 subscriptions to the same presentity from the same RLS which are to 233 receive the same view. When a presence notification is to be sent, 234 instead of sending it on all subscriptions, the notification is sent 235 on just a single subscription. 237 Should the authorization policies in the serving domain change, an 238 updated ACL is sent, informing the watching domain of the new 239 policies. This may require the watching domain to extend a back-end 240 subscription to obtain a view, or may change the view an existing 241 watcher is receiving, and so on. 243 The ACL allows the serving domain a great deal of flexibility in the 244 level of trust it imparts to the watching domain. The following are 245 all possible approaches that the serving domain can utilize: 247 Minimal Trust: When a watcher subscribes to a presentity, the ACL 248 generated for that subscription includes only that watcher, along 249 with an identifier for their view. Consequently, for each watcher 250 in domain 1 there will be a backend subscription to domain 2. 251 However, should multiple watchers share the same view, the 252 presence server in domain 2 sends a single presence document on 253 one of the subscriptions, and the RLS uses this for all of the 254 other watchers with the same view. With this approach, domain 2 255 never discloses the list of authorized watchers ahead of time, and 256 it has full knowledge of each watcher that is subscribed. 257 However, it gets the performance benefits of reducing the amount 258 of notification traffic. 260 Partial Trust: When a watcher subscribes to a presentity, the ACL 261 generated for that subscription includes that watcher and all 262 other watchers authorized for that same view. Consequently, there 263 will only be one backend subscription from the RLS to the presence 264 server for each view. However, the full set of authorized 265 watchers is not disclosed ahead of time, only those that will get 266 the same view. With partial trust, the presence server will not 267 know the full set of watchers currently subscribed. 269 Full Trust: When a watcher subscribes to a presentity, the ACL 270 generated for that subscription includes that watcher and all 271 other watchers that are authorized for that view, and all other 272 views, along with a rule that says that all other watchers get 273 rejected. In this case, as with partial trust, there is only one 274 backend subscription from the RLS to the presence server for each 275 view. The full set of watchers is disclosed ahead of time as 276 well. The presence server will not know the full set of watchers 277 currently subscribed. 279 3. RLS Behavior 281 This section defines the procedures that are to be followed by the 282 RLS. It is important to note that, even though this specification 283 defines an extension to the SIP events framework, that extension is 284 only useful for the back-end subscriptions generated by an RLS. The 285 extension defined here is not applicable or useful for individual 286 users generating subscriptions. Indeed, if it were utilized by 287 individual users, it has the potential for violations of user 288 privacy. See Section 8 for a discussion. 290 3.1. On Receipt of a Resource List Subscription Request 292 When the RLS receives a subscription to a resource list which 293 includes some presentity P in another domain, it follows the rules 294 defined here. 296 3.1.1. Authentication and Authorization 298 First, the RLS MUST check a configured list of peer domains for which 299 this extension is to be applied. Because of the potential privacy 300 disclosures involved in unauthorized use of this facility, it can 301 only be used between pairs of domains which have a pre-arranged 302 agreement to utilize it. If the domain of the presentity P matches 303 one of the configured list of peer domains, the RLS is permitted to 304 utilize this extension. If not, the extension MUST NOT be used. 306 Next, the RLS MUST send the SUBSCRIBE request over a mutually 307 authenticated TLS connection. The RLS MUST check that the 308 subjectAltName in the certificate of its peer contains a domain name 309 that is a match for the domain of the URI of the presentity. If they 310 are not a match, view sharing cannot be utilized for this 311 subscription. 313 The procedures followed by the RLS after this point depend on whether 314 the RLS already has a backend subscription to the presentity that is 315 in the active state, and for which an ACL has been received. 317 3.1.2. No Active Back-End Subscription 319 The RLS MUST generate a back-end subscription to obtain the state of 320 the presentity. The RLS MUST include a Supported header field in the 321 request with the option tag "view-share". The Accept header field 322 MUST be present in the request and MUST include the "application/ 323 aclinfo+xml" MIME type amongst the list of supported types. 325 Note that it is possible that two watchers, in a short period of 326 time, both subscribe to their resource lists, both of which include 327 presentity P. This will cause the RLS to generate two back-end 328 subscriptions at around the same time. The RLS is forced to generate 329 the second back-end subscription because it doesn't have an active 330 back-end subscription that has yet generated an ACL. Once both 331 subscriptions become active and generate ACLs, if the watchers are 332 receiving the same view and both ACLs contain both watchers, the RLS 333 SHOULD terminate one of the back-end subscriptions. 335 3.1.3. Active Back-End Subscription 337 In this case, the RLS already has at least one back-end subscription 338 to the target presentity P, and it has received at least one ACL for 339 that presentity. It has received a resource list subscription from 340 watcher W which includes presentity P. Based on the procedures of 341 Section 3.2.1, the RLS will keep, for each presentity, the list of 342 the most recent ACLs received on each back-end subscription currently 343 in place. This is called the current ACL list. 345 For each ACL Ai in the current ACL list, the RLS performs the rule 346 determination algorithm of Section 5.4 to compute the rule ID for the 347 watcher W. This represents the view that the watcher is supposed to 348 receive. 350 Next, the RLS goes through all subscriptions it currently has for 351 presentity P. For each one, it takes the identity of the watcher for 352 that actual subscription. The identity for the watcher for that 353 actual subscription is equal to the asserted identity included in the 354 back-end subscription. For example, if SIP Identity [RFC4474] is 355 utilized, this would be the URI present in the From header field of 356 the back-end SUBSCRIBE. Call the watcher identity for each 357 subscription Wj. 359 Next, the RLS computes the rule determination algorithm of 360 Section 5.4 to compute the rule ID Rj for the watcher Wj on each 361 subscription j. This represents the rule ID for the view being 362 delivered on that subscription. 364 Then, processing depends on the values of R and Rj: 366 o If R is null, it means that the ACL doesn't specify the view for 367 this watcher. The RLS MUST generate a back-end subscription to 368 presentity P, and MUST use watcher W as the identity in the back- 369 end subscription. 371 o If R is not null, but the associated rule is blocked, it means 372 that the watcher will be rejected. The RLS SHOULD NOT perform 373 another back-end subscription, and must act as if it had created a 374 back-end subscription which was rejected. 376 o If R was not null, and there is at least one subscription j for 377 which Rj = R, it means that subscription j is already generating 378 notifications for the view that watcher W is supposed to receive. 379 In that case, the RLS SHOULD NOT generate a back-end subscription 380 for P on behalf of W. Rather, it should treat the existing back 381 end subscription j as if it were the back-end subscription for W, 382 and follow the guidelines of RFC 4662 [RFC4662] based on that. 383 Subscription j is called the generating subscription for watcher 384 W, and the actual watcher associated with subscription j, Wj, is 385 called the generating watcher Wgen for watcher W. 387 o If R was not null, but there is no subscription j for which Rj=R, 388 it means that the RLS is not yet receiving the view that watcher W 389 requires. The RLS MUST generate a back-end subscription to 390 presentity P, and MUST use watcher W as the identity in the back- 391 end subscription. 393 3.2. Processing NOTIFY Requests 395 If a NOTIFY request arrives with a Require header field that includes 396 the "view-share" option tag, it MUST be processed according to the 397 rules of this specification. 399 3.2.1. Processing ACL-Infos 401 If the contents of the NOTIFY are of type "application/aclinfo+xml", 402 the subscriber processes the body as described here. 404 For each presentity that the RLS has at least one back-end 405 subscription for, the RLS MUST remember the most recent aclinfo 406 received on each back-end subscription. This is called the current 407 ACL list for the presentity. This set of aclinfo is used in the 408 processing of subscription requests, as described in Section 3.1.3. 410 The serving domain can change policies at any time. When it does, it 411 sends an updated ACL on one or more subscriptions. The RLS MUST 412 store this ACL. Furthermore, the ACL might impact the views being 413 received by watchers, and may impact the state of the back-end 414 subscriptions. 416 The RLS computes the set of watchers Wi which have a resource list 417 subscription that includes the presentity P for whom an updated ACL 418 has just been received. For each Wi, it performs the view 419 determination algorithm (see Section 5.4 on the current ACL set. Let 420 Ri be the view associated with watcher Wi. If Ri has not changed 421 from prior to the receipt of the new ACL, no action is taken. 422 However, if it has changed, the RLS takes the set of current back-end 423 subscriptions, and for each subscription j, computes the view 424 determination algorithm for its associated watcher Wj, to produce Rj. 425 The action to take depends on what has changed: 427 o If Ri is now null, it means that the serving domain has changed 428 the views associated with watcher Wi, and this new view is not 429 known to the RLS. The RLS MUST generate a new back-end 430 subscription on behalf of watcher Wi for presentity P to obtain 431 this view. 433 o If Ri is now a blocked rule, it means that the serving domain has 434 now blocked Wi from obtaining the presence of the presentity. The 435 RLS must act as if it had a back-end subscription on behalf of 436 watcher Wi which was terminated. 438 o If Ri is not null and not blocked, and if there is an Rj which 439 matches the new Ri, it means that the serving domain has changed 440 the views associated with watcher Wi, and changed them to another 441 view already being received by the RLS. The RLS MUST treat this 442 back-end subscription j as if it were the back-end subscription to 443 presentity P for watcher Wi. If the most recent presence document 444 received on this back-end subscription is not a semantic match for 445 the presence document most recently delivered to Wi for presentity 446 P, the RLS MUST send this most recent presence document to watcher 447 Wi. 449 o If Ri is not null and not blocked, but there is no Rj which 450 matches the new Ri, it means that the serving domain has changed 451 the views associated with watcher Wi, and this new view is not one 452 currently being delivered to the RLS. The RLS MUST generate a new 453 back-end subscription on behalf of watcher Wi for presentity P to 454 obtain this view. 456 Furthermore, if there are now two back-end subscriptions j1 and j2 457 for which Aj1 = Aj2, the RLS SHOULD terminate one of those two 458 subscriptions. Two ACL documents are considered equal if they 459 enumerate the same set of rules with the same members for each rule. 461 3.2.2. Processing Presence Documents 463 If the contents of the NOTIFY is a presence document, the RLS follows 464 the procedures defined here. 466 Let Wj be the watcher on the subscription j on which the presence 467 document was just received. Let Rj be the results of running the 468 rule determination algorithm on Wj using the current ACL set. Next, 469 the RLS takes the set of watchers Wi which have presentity P on their 470 buddy lists. The RLS then runs the rule determination algorithm on 471 each Wi using the current ACL set, producting Ri for each watcher Wi. 473 For each Ri that is equal to Rj, the RLS MUST utilize the presence 474 document just received as if the back-end subscription j was in fact 475 for watcher Wi. This will typically cause that presence document to 476 be sent in a NOTIFY request to each such watcher, though each watcher 477 may have some kind of filtering policy which causes the RLS to modify 478 the document prior to delivery. 480 3.2.3. Processing Back-End Terminations 482 If the NOTIFY request from the serving domain terminates the back-end 483 subscription, it may be because the watcher Wj associated with that 484 subscription is no longer permitted to view the presence of the 485 presentity. 487 The ACL associated with the subscription MUST be removed from the 488 current ACL set. The procedures of Section 3.2.1 MUST be performed 489 to adjust back-end subscriptions, if needed. 491 4. Presence Agent Behavior 493 When a presence agent receives a SUBSCRIBE request containing a 494 Supported header with the value "view-share", and it wishes to 495 utilize view sharing for this subscription, it follows the procedures 496 defined here. 498 4.1. Authentication and Authorization 500 First, the presence agent MUST have received the SUBSCRIBE request 501 over a mutually authenticated TLS connection. If it had not, view 502 sharing cannot be utilized for this subscription. The presence agent 503 MUST check that the subjectAltName in the certificate of its peer 504 contains a domain name that is a match for the domain of the URI of 505 the watcher. If they are not a match, view sharing cannot be 506 utilized for this subscription. 508 Assuming they are a match, the presence agent MUST check a configured 509 list of peer domains for which this extension is to be applied. 510 Because of the potential privacy disclosures involved in unauthorized 511 use of this facility, it can only be used between pairs of domains 512 which have a pre-arranged agreement to utilize it. If the domain of 513 the watcher W matches one of the configured list of peer domains, the 514 presence agent is permitted to utilize this extension. If not, the 515 extension MUST NOT be used. 517 4.2. Processing Initial SUBSCRIBE Requests 519 First, the subscription is processed as it normally would be, 520 including authorization and policy around the presence document to be 521 delivered to the watcher. Furthermore, if the presence agent wishes 522 to utilize view sharing for this subscription, it MUST include a 523 Require header field in the first NOTIFY request (and indeed any 524 subsequent ones) it sends confirming this subscription, and that 525 NOTIFY MUST contain the "view-share" option tag. 527 Furthermore, the initial state sent by the presence agent MUST 528 include an ACL document. It is formatted according to the rules and 529 considerations in Section 5. 531 The initial state sent by the presence agent might include an actual 532 presence document. In particular, a presence document MUST be sent 533 if one of the following is true: 535 o There is only one subscription from the watching domain to this 536 presentity that has the view associated with the watcher. 538 o There is more than one subscription from the watching domain to 539 this presentity with the same view, but the User-Agent header 540 field in the request differs between them. 542 If one of these conditions is not true, the presence agent SHOULD NOT 543 send an initial presence document on this subscription. 545 OPEN ISSUE: This bit about user agent is trying to address the 546 case where there are a multiplicity of RLS in the originating 547 domain, each of which serves a different subset of the watcher 548 population. If two watchers get the same view, but are served by 549 different RLS, presence state must be sent to each. There needs 550 to be some way to indicate to the presence agent that 551 subscriptions come from different RLS. Other choices besides 552 User-Agent are the Via header field or the TLS certificate. There 553 are pros and cons to each choice. Possibly a separate header 554 field for this? 556 If an ACL and a presence document are to be delivered, they MUST be 557 delivered in a separate NOTIFY request (unless the subscriber 558 indicated support for multipart, in which case the content MAY be 559 included in a single NOTIFY with mulitpart content). 561 4.3. SUBSCRIBE Refreshes 563 When the presence agent receives a SUBSCRIBE refresh, it MUST send 564 the most recent ACL document, and if presence documents are being 565 sent for this subscription, the most recent presence document. 567 4.4. Policy Changes 569 There are several different types of policy changes that can occur: 571 o If the definitions for a particular rule change, the presence 572 agent MUST assign a new rule ID for that rule. For each 573 subscription to a presentity which contained that rule, the 574 presence agent MUST send an updated ACL which includes a rule with 575 this new rule ID. 577 o If some watcher W was previously associated with rule X and is now 578 associated with rule Y, the presence agent checks if it has any 579 subscriptions from watcher W. If it does, it MUST send an updated 580 ACL on that subscription. Based on the rules in Section 5, this 581 ACL will contain rule Y and will at least include W amongst the 582 list of members. Furthermore, if there were subscriptions from 583 other watchers, but the presence agent had previously sent an ACL 584 on the subscription which was a match for W, it MUST send an 585 updated ACL on that subscription. This updated ACL MAY omit a 586 statement about rule Y or MAY include it. However, the updated 587 ACL MUST NOT claim that watcher W will receive rule X. 589 o If some watcher W was previously associated with rule X and is now 590 blocked, the presence agent checks if it has any subscriptions 591 from watcher W. If it does, it MUST terminate the back-end 592 subscription. If it doesn't, but it has a subscription from some 593 other watcher which had included a rule that was a match for W, 594 the presence agent MUST send an updated ACL on that subscription. 595 This updated ACL MAY omit any statement about watcher W, or MAY 596 include them as part of a blocked rule in that ACL. 598 o If some watcher W was previously blocked and is now permitted and 599 associated with some rule X, the presence agent checks if it had 600 any subscriptions from some other watcher which included a blocked 601 rule that matched watcher W. If it had, it MUST send an updated 602 ACL on that subscription. That updated ACL MAY omit any statement 603 about watcher W, or MAY indicate that watcher W is now associated 604 with rule X. 606 Of course, a policy change will also potentially alter the presence 607 documents that are associated with a view. If so, the presence agent 608 MUST send an updated document on a subscription if one of the 609 following is true: 611 o There is only one subscription from the watching domain to this 612 presentity that has the view associated with the watcher. 614 o There is more than one subscription from the watching domain to 615 this presentity with the same view, but the User-Agent header 616 field in the request differs between them. 618 If neither is true, the presence agent MUST select one subscription 619 amongst the several which share the same presentity, view, and User- 620 Agent header field, and sent an updated notification on that 621 subscription. The choice of subscriptions is arbitrary and MAY 622 change for each notification. 624 4.5. Presence State Changes 626 If the state of some presentity changes, the presence agent may need 627 to send an updated notification on a subscription. The presence 628 agent MUST send an update on a subscription if one of the following 629 is true: 631 o There is only one subscription from the watching domain to this 632 presentity that has the view associated with the watcher. 634 o There is more than one subscription from the watching domain to 635 this presentity with the same view, but the User-Agent header 636 field in the request differs between them. 638 If neither is true, the presence agent MUST select one subscription 639 amongst the several which share the same presentity, view, and User- 640 Agent header field, and sent an updated notification on that 641 subscription. The choice of subscriptions is arbitrary and MAY 642 change for each notification. 644 5. ACL Format 646 An ACL document is an XML [W3C.REC-xml-20001006] document that MUST 647 be well-formed and MUST be valid according to schemas, including 648 extension schemas, available to the validater and applicable to the 649 XML document. ACL documents MUST be based on XML 1.0 and MUST be 650 encoded using UTF-8. This specification makes use of XML namespaces 651 for identifying ACL documents and document fragments. The namespace 652 URI for elements defined by this specification is a URN [RFC2141], 653 using the namespace identifier 'ietf' defined by RFC 2648 [RFC2648] 654 and extended by RFC 3688 [RFC3688]. This URN is: 656 urn:ietf:params:xml:ns:aclinfo 658 5.1. Document Structure and Semantics 660 An ACL document informs a watching domain of the set of views that 661 can be received by that domain, and associates specific watchers with 662 specific views. It is very important to understand that the ACL 663 document does not convey the actual processing that will be applied 664 by the serving domain. It does not indicate, for example, whether 665 geolocation is present in a presence document, or which rich presence 666 [RFC4480] data elements will be conveyed. It merely provides 667 grouping - indicating which watchers from the watching domain will 668 receive the same view. 670 Each ACL document starts with the enclosing root element . 671 This contains the list of rules defined by the ACL. Each rule is 672 represented by the element. Each rule represents a specific 673 view, which is generated by the presence server based on its 674 authorization, composition and filtering policies. Each rule is 675 associated with a rule ID, which is a mandatory attribute of the 676 element. This ID is scoped within a single presentity. That 677 is, the IDs for two rules for different presentities are unrelated. 679 The element also contains an optional "blocked" boolean 680 attribute. If "true", it means that the rule specifies that the 681 associated set of watchers will be rejected, should they subscribe. 682 This can be used by the watching domain to avoid performing back-end 683 subscriptions to users which will only be blocked anyway. 685 Each contains the set of users that will receive the 686 corresponding view. This can be described by an enumerated set or by 687 a default. If it is an enumerated set, the is followed by a 688 sequence of elements, each of which contains a SIP URI for 689 the watcher that will receive that view. 691 The default view is specified by including a single child element for 692 - . The default view applies to all watchers except 693 those enumerated by other rules. For this reason, an ACL document 694 which contains a default view MUST include the rule IDs and 695 associated members for all other views that are delivered to 696 watchers. For example, consider a presentity that has three views. 697 View 1 is delivered to watchers A and B. View 2 is delivered to 698 watcher C. View 3 is delivered to everyone else. An ACL document 699 that includes the default view must also include views 1 and 2 with 700 watchers A, B, and C. 702 In contrast, an ACL document that does not include a default does not 703 need to include all views, and it does not need to include all 704 members for a particular view. Using the example above, it is valid 705 to include an ACL document which includes only view 1 with watcher 1. 707 If two URI are present within elements within the same 708 , it represents a contract by the presence server that both 709 users MUST get the same view. Formally, if the presence server were 710 to receive a subscription from each watcher, both subscriptions would 711 be accepted or both would be rejected, and if accepted, each 712 subscription would receive semantically identical presence documents 713 at approximately the same time. 715 Even if two users will receive the same view, a presence server MAY 716 assign each to a different view ID. There is no requirement that two 717 unique views actually contain different presence data. The only 718 requirement is that, if two users are listed within the same rule, 719 that they do in fact receive the same view. 721 An ACL document delivered in a subscription from watcher W MUST 722 include the view associated with watcher W and MUST include watcher W 723 explicitly in a element or implicitly by presence of an 724 element. 726 5.2. Trust Considerations when Construcing ACLs 728 The semantics above give very little guidance about what a presence 729 server should include in an ACL. The amount of information to convey 730 depends on the level of trust between the watching and serving 731 domains. 733 Optimal performance is achieved when the ACL document for a 734 presentity includes all views that the server might ever deliver, and 735 includes all members for each view, including any defaults and 736 blocked rules. However, this informs the watching domain of the set 737 of allowed and blocked watchers, and associated groupings amongst 738 watchers. 740 Slightly worse performance is achieved when the ACL document for a 741 presentity sent in a subscription from watcher W includes only a 742 single view - the one for watcher W - along with the full set of 743 watchers which will also receive that view, assuming it is not the 744 default view. If the view is the default view, the document can 745 include just watcher W. This approach will cause back-end 746 subscriptions from every watcher that will receive the default, but 747 it discloses less information to the watching domain. In particular, 748 the full set and number of views is never known by the watching 749 domain. The fact that a view is default is never known by the 750 watching domain. The full set of users that are permitted to view 751 the presence of the presentity is never disclosed to the watching 752 domain. The performance of this approach is still reasonably good 753 when the default rule is blocked. However it is much less effective 754 when the default is not blocked, and many watchers receive the 755 default. 757 Another choice for construction of ACL documents is to include, in a 758 subscription from watcher W, a single rule containing the rule ID for 759 the view that watcher W will receive, along with a single member - W. 760 This approach will still result in a back-end subscription from each 761 watcher. However, a single notification is sent for each view, 762 rather than one per watcher. The benefit of this construction is 763 that it provides the watching domain no additional information about 764 the authorization policies of the presentity than if this extension 765 were not in use at all. 767 5.3. Example Documents 769 The example document in Figure 2 shows the case when there is maximum 770 trust between domains. The full set of watchers, include a blocked 771 default, is included. 773 774 775 776 777 sip:user1@example.com 778 sip:user2@example.com 779 sip:user3@example.com 780 sip:user4@example.com 781 sip:user5@example.com 782 783 784 sip:user6@example.com 785 786 787 sip:user7@example.com 788 sip:user8@example.com 789 sip:user9@example.comm 790 sip:user10@example.com 791 sip:user11@example.com 792 793 794 795 796 798 Figure 2: Example with Maximum Trust 800 The example in Figure 3 shows a moderate level of trust. This ACL 801 only shows the view associated with the watcher user1. 803 804 805 806 807 sip:user1@example.com 808 sip:user2@example.com 809 sip:user3@example.com 810 sip:user4@example.com 811 sip:user5@example.com 812 813 815 Figure 3: Example with Partial Trust 817 The example in Figure 4 shows the minimal level of trust. This ACL 818 would be sent in a subscription to user1. 820 821 822 823 824 sip:user1@example.com 825 826 828 Figure 4: Example with Minimal Trust 830 5.4. Rule Determination Algorithm 832 Several steps in the processing of the ACL require that the RLS in 833 the watching domain execute the rule determination algorithm for 834 watcher W on an ACL set. This algorithm is a simple algorithm which 835 takes, as input, a watcher W with a given SIP URI, and a set of ACL 836 documents Ai, and returns as output, a rule ID R, which is the rule 837 ID for the view that, according to the set of ACLs, watcher W should 838 receive. 840 The algorithm proceeds as follows. First, each Ai is matched to W. 841 ACL Ai is a match for watcher W if: 843 o ACL Ai contains a tag whose URI is a match, based on URI 844 equality, for W, or 846 o none of the tags in Ai contain a URI that is a match, 847 based on URI equality, for W, but there is an element in 848 Ai 850 If no ACL Ai matched, the algorithm returns a null result. 852 For each ACL Ai that matches based on the rules above, take the id of 853 the enclosing element that contained the or 854 element that caused the match. For ACL Ai, this is rule Ri. For 855 example, consider the following ACL: 857 858 859 860 sip:user1@example.com 861 sip:user2@example.com 862 863 864 sip:user3@example.com 865 866 867 868 869 871 If this document is A1, and the watcher is sip:user3@example.com, the 872 associated rule R1 is 2. If the watcher is sip:user1@example.com or 873 sip:user2@example.com, the rule R1 is 1. If the watcher is anyone 874 else from example.com, such as sip:user4@example.com, the rule R1 is 875 3. 877 If all Ri are equal, denote R = Ri. Thus, R is the rule ID 878 associated with this watcher. Normally, all Ri will be equal. 879 However, during transient periods of changes in authorization state, 880 it is possible that inconsistent ACL documents exist. In that case, 881 R is assigned the value Ri from the ACL Ai which is the most recently 882 received amonst all ACL. 884 5.5. XML Schema 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 909 6. Performance Analysis 911 This section considers the performance improvement of the mechanism 912 when it is maximally exercised. In that case, the full ACL, 913 including blocked senders, is returned in the first subscription to a 914 presentity. This analysis assumes there is a single, monolithic 915 presence server serving each domain. 917 The optimizations improve ramp-up, steady state, and termination 918 message loads. IN particular, each of those loads, without the 919 optimization described here, is proportional to C04, the total number 920 of federated presentities per watcher. If we assume symmetry, such 921 that the number of federated presentities per watcher is equal to the 922 number of watchers per federated presentity, then each of the load 923 figures is reduced by C04. That is, the system behaves identically 924 to the case where there is a single watcher per federated presentity, 925 and assuming symmetric, the same as if there is a single federated 926 presentity per watcher - e.g., C04 = 1. 928 Consider then the very large network peering model in 930 [I-D.ietf-simple-interdomain-scaling-analysis]. In this model, the 931 assumption is two large peering domains with 20 million users each, 932 with a value of 10 for C04. With this optimization, the number of 933 steady state notifications due to presence state changes drops from 934 18.4 billion per day to 1.84 billion per day. The number of messages 935 per second overall is reduced from 654,167 per second to 65,417 per 936 second. Still a big number, of course, but it can't actually get 937 much smaller. 939 Indeed, it can be readily shown that, assuming the federated domains 940 do not actually share raw presence inputs and the actual policies 941 that govern operation of their servers, no protocol can do better 942 (constants, such as mesage size and the need for protocol responses 943 and acknowledgements aside). Consider a domain with N presentities. 944 Each presentity changes state P times per hour. Every time the state 945 changes, the domain applies its authorization and composition 946 policies. The resulting presence document cannot be known to the 947 watching domain. Thus, there must be at least one message from the 948 serving to watching domain, per view, in order to inform it of that 949 view. This means that the steady state rate of messages can never be 950 better than N*P, and this is exactly the factor governing the rate of 951 messages when this optimization is applied. 953 7. Requirements Analysis 955 This section analyzes the requirements in 956 [I-D.houri-sipping-presence-scaling-requirements] to show how they 957 are met by the mechanism proposed here. 959 REQ-001: The solution should not hinder the ability of existing 960 SIMPLE clients and/or servers from peering with a domain or client 961 implementing the solution. No changes may be required of existing 962 servers to interoperate. This requirement is met by usage of the 963 Supported and Require mechanisms and SIP which negotiate its 964 usage. 966 REQ-002: It does NOT constrain any existing RFC functional or 967 security requirements for presence. The mechanism does not change 968 anything that is possible without it. It does, however, introduce 969 new privacy considerations, described below in Section 8. 971 REQ-003: Systems that are not using the new additions to the 972 protocol should operate at the same level as they do today. This 973 requirement is met by usage of the Supported and Require 974 mechanisms in SIP. 976 REQ-004: The solution does not limit the ability for presentities to 977 present different views of presence to different watchers. This 978 requirement is met by usage of the ACL document, which allows the 979 serving domain to associate a watcher with any view it likes, and 980 to change it over time. 982 REQ-005: The solution does not restrict the ability of a presentity 983 to obtain its list of watchers. The mechanism does allow a 984 presence server to know the list of watchers, at the expense of 985 non-optimal performance. In particular, it will receive a 986 subscription from each watcher. However, it only generates one 987 notification per view on presence changes. The fully optimized 988 solution will result in a loss of knowledge of the set of 989 watchers. However, it is a policy decision at the presence agent 990 about whether it would like to make this tradeoff. 992 REQ-006: The solution MUST NOT create any new or make worse any 993 existing privacy holes. This requirement is met, but only when 994 carefully provisioned. See Section 8. 996 REQ-007: It is highly desirable for any presence system (intra or 997 inter-domain) to scale linearly as number of watchers and 998 presentities increase linearly. When the most optimal technique 999 is used, there is always one subscription per view per presentity, 1000 independent of the number of watchers in the remote domain or the 1001 number of averages buddies per buddy list. Since the number of 1002 views is not proportional to the number of users, the total 1003 traffic volume in a domain is linear with its number of 1004 presentities, and is independent of the number of users in the 1005 peering domain. 1007 REQ-008: The solution SHOULD NOT require significantly more state in 1008 order to implement the solution. The mechanism requires storage 1009 of the ACL, which has a size exactly equal to the number of 1010 subscriptions that would be required if the extension were not in 1011 place. Thus the memory usage is not worsened compared to the 1012 baseline. 1014 REQ-009: It MUST be able to scale to tens of millions of concurrent 1015 users in each domain and in each peer domain. The analysis in 1016 Section 6 shows that, when fully utilized, this mechanism is the 1017 best that can possibly be achieved in any system that does not 1018 actually share policies and raw presence data. 1020 REQ-010: It MUST support a very high level of watcher/presentity 1021 intersections in various intersection models. The mechanism is 1022 optimized for this case. 1024 REQ-011: Protocol changes MUST NOT prohibit optimizations in 1025 different deployment models esp. where there is a high level of 1026 cross subscriptions between the domains. Since standard SIP 1027 techniques are utilized to negotiate the extension, other 1028 mechansims can be defined in the future. 1030 REQ-012: New functionalities and extensions to the presence protocol 1031 SHOULD take into account scalability with respect to the number of 1032 messages, state size and management and processing load. That is 1033 exactly what this extension targets. 1035 REQ-013: The solution SHOULD allow for arbitrary federation 1036 topologies including direct peering and intermediary routing. The 1037 mechanism is optimized for direct peering. It can work in 1038 intermediary routing cases as well. 1040 8. Security Considerations 1042 The principal question with the specification is whether it alters 1043 the privacy characteristics of a non-optimized federated system. 1045 Consider first the case where the serving domain is using the minimal 1046 trust model. In that case, the ACL provided to the watching 1047 information does not carry any information that the watching domain 1048 doesn't already know. It merely points out when two watchers share 1049 the same view. This is something that the watching domain could have 1050 already ascertained by comparing presence documents delivered to each 1051 watcher. The ACL makes this task easier, but nonetheless the 1052 watching domain could have already ascertained it. Consequently, 1053 there is no change whatsoever in the level of privacy afforded by the 1054 optimization when this mode is used. 1056 However, when an ACL is provided that includes other users besides 1057 the actual watcher, this provides additional information to the 1058 watching domain. This is, however, information that the watching 1059 domain could find out anyway. If it generated a subscription from 1060 each of its users to the presentity it would be able to determine who 1061 from its domain is allowed to subscribe and what view they would 1062 receive. This would be an expensive operation to be sure, but it is 1063 possible. Consequently, the optimization doesn't really provide 1064 anything new to the originating domain, even in this case. 1066 However, there is an attack possible when the information is divulged 1067 to an end user. Consider a watching domain that doesn't actually 1068 implement this extension at all. A user within the domain uses a 1069 client that generates a subscription to a presentity in a remote 1070 domain. This subscription uses an outbound proxy in the watching 1071 domain. The outbound proxy is just a proxy, and therefore doesn't 1072 remove or modify the Supported header field in the request. The 1073 serving domain accepts the subscription and sends an ACL that 1074 contains the full set of watchers that are permitted in the 1075 originating domain. The original watcher now knows the set of other 1076 authorized buddies within their own domain, and what views they will 1077 see. While this is information that the domain overall would have 1078 access to, it is not information an end user would normally have 1079 access to. Consequently, this is a more serious privacy violation. 1081 It is for this reason that this specification requires that both 1082 sides of the federated link be explicitly provisioned to utilize this 1083 optimization. In the attack above, the watching domain would not 1084 have set up a peering relationship with the serving domain. If it 1085 had, it would have an RLS and would not have permitted the user to 1086 directly subscribe in this way. Thus, when the subscription is 1087 received by the serving domain, it will find that it has no agreement 1088 with the originating domain, and would not utilize view sharing. 1089 This thwarts the attack. 1091 This remedy is not optimal because it requires on provisioning to 1092 prevent. There does not appear to be any easy cryptographic means to 1093 prevent it, however. 1095 9. IANA Considerations 1097 There are several IANA considerations associated with this 1098 specification. 1100 9.1. MIME Type Registration 1102 This specification requests the registration of a new MIME type 1103 according to the procedures of RFC 2048 [RFC2048] and guidelines in 1104 RFC 3023 [RFC3023]. 1106 MIME media type name: application 1108 MIME subtype name: aclinfo+xml 1110 Mandatory parameters: none 1112 Optional parameters: Same as charset parameter application/xml as 1113 specified in RFC 3023 [RFC3023]. 1115 Encoding considerations: Same as encoding considerations of 1116 application/xml as specified in RFC 3023 [RFC3023]. 1118 Security considerations: See Section 10 of RFC 3023 [RFC3023] and 1119 Section 8 of RFC XXXX [[NOTE TO IANA/RFC-EDITOR: Please replace 1120 XXXX with the RFC number of this specification]]. 1122 Interoperability considerations: none. 1124 Published specification: RFC XXXX [[NOTE TO IANA/RFC-EDITOR: 1125 Please replace XXXX with the RFC number of this specification]] 1127 Applications which use this media type: This document type has 1128 been used to support subscriptions to lists of users [RFC4662] for 1129 SIP-based presence [RFC3856]. 1131 Additional Information: 1133 Magic Number: None 1135 File Extension: .acl 1137 Macintosh file type code: "TEXT" 1139 Personal and email address for further information: Jonathan 1140 Rosenberg, jdrosen@jdrosen.net 1142 Intended usage: COMMON 1144 Author/Change controller: The IETF. 1146 9.2. URN Sub-Namespace Registration 1148 This section registers a new XML namespace, as per the guidelines in 1149 RFC 3688 [RFC3688]. 1151 URI: The URI for this namespace is urn:ietf:params:xml:ns:aclinfo. 1153 Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org), 1154 Jonathan Rosenberg (jdrosen@jdrosen.net). 1156 XML: 1158 BEGIN 1159 1160 1162 1163 1164 1166 ACL Info Namespace 1167 1168 1169

Namespace for ACL Info

1170

urn:ietf:params:xml:ns:aclinfo

1171

See RFCXXXX [NOTE 1172 TO IANA/RFC-EDITOR: Please replace XXXX with the RFC number of this 1173 specification.].

1174 1175 1176 END 1178 9.3. Schema Registration 1180 This section registers an XML schema per the procedures in [RFC3688]. 1182 URI: urn:ietf:params:xml:schema:aclinfo 1184 Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org), 1185 Jonathan Rosenberg (jdrosen@jdrosen.net). 1187 The XML for this schema can be found as the sole content of 1188 Section 5.5. 1190 10. References 1192 10.1. Normative References 1194 [RFC4662] Roach, A., Campbell, B., and J. Rosenberg, "A Session 1195 Initiation Protocol (SIP) Event Notification Extension for 1196 Resource Lists", RFC 4662, August 2006. 1198 [RFC4474] Peterson, J. and C. Jennings, "Enhancements for 1199 Authenticated Identity Management in the Session 1200 Initiation Protocol (SIP)", RFC 4474, August 2006. 1202 [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. 1204 [RFC2648] Moats, R., "A URN Namespace for IETF Documents", RFC 2648, 1205 August 1999. 1207 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 1208 January 2004. 1210 [RFC2048] Freed, N., Klensin, J., and J. Postel, "Multipurpose 1211 Internet Mail Extensions (MIME) Part Four: Registration 1212 Procedures", BCP 13, RFC 2048, November 1996. 1214 [RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media 1215 Types", RFC 3023, January 2001. 1217 [W3C.REC-xml-20001006] 1218 Maler, E., Paoli, J., Bray, T., and C. Sperberg-McQueen, 1219 "Extensible Markup Language (XML) 1.0 (Second Edition)", 1220 World Wide Web Consortium FirstEdition REC-xml-20001006, 1221 October 2000, 1222 . 1224 10.2. Informative References 1226 [RFC2778] Day, M., Rosenberg, J., and H. Sugano, "A Model for 1227 Presence and Instant Messaging", RFC 2778, February 2000. 1229 [RFC3863] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, 1230 W., and J. Peterson, "Presence Information Data Format 1231 (PIDF)", RFC 3863, August 2004. 1233 [RFC4479] Rosenberg, J., "A Data Model for Presence", RFC 4479, 1234 July 2006. 1236 [RFC3856] Rosenberg, J., "A Presence Event Package for the Session 1237 Initiation Protocol (SIP)", RFC 3856, August 2004. 1239 [RFC4480] Schulzrinne, H., Gurbani, V., Kyzivat, P., and J. 1240 Rosenberg, "RPID: Rich Presence Extensions to the Presence 1241 Information Data Format (PIDF)", RFC 4480, July 2006. 1243 [I-D.ietf-simple-interdomain-scaling-analysis] 1244 Houri, A., "Presence Interdomain Scaling Analysis for SIP/ 1245 SIMPLE", draft-ietf-simple-interdomain-scaling-analysis-01 1246 (work in progress), July 2007. 1248 [I-D.ietf-sip-subnot-etags] 1249 Niemi, A., "An Extension to Session Initiation Protocol 1250 (SIP) Events for Conditional Event Notification", 1251 draft-ietf-sip-subnot-etags-00 (work in progress), 1252 May 2007. 1254 [I-D.houri-sipping-presence-scaling-requirements] 1255 Houri, A., "Scaling Requirements for Presence in SIP/ 1256 SIMPLE", 1257 draft-houri-sipping-presence-scaling-requirements-00 (work 1258 in progress), July 2007. 1260 Authors' Addresses 1262 Jonathan Rosenberg 1263 Cisco 1264 Edison, NJ 1265 US 1267 Phone: +1 973 952-5000 1268 Email: jdrosen@cisco.com 1269 URI: http://www.jdrosen.net 1271 Steve Donovan 1272 Cisco 1273 Richardson, TX 1274 US 1276 Email: stdonova@cisco.com 1278 Kathleen McMurry 1279 Cisco 1280 Richardson, TX 1281 US 1283 Email: kmcmurry@cisco.com 1285 Full Copyright Statement 1287 Copyright (C) The IETF Trust (2007). 1289 This document is subject to the rights, licenses and restrictions 1290 contained in BCP 78, and except as set forth therein, the authors 1291 retain all their rights. 1293 This document and the information contained herein are provided on an 1294 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 1295 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 1296 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 1297 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1298 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1299 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1301 Intellectual Property 1303 The IETF takes no position regarding the validity or scope of any 1304 Intellectual Property Rights or other rights that might be claimed to 1305 pertain to the implementation or use of the technology described in 1306 this document or the extent to which any license under such rights 1307 might or might not be available; nor does it represent that it has 1308 made any independent effort to identify any such rights. Information 1309 on the procedures with respect to rights in RFC documents can be 1310 found in BCP 78 and BCP 79. 1312 Copies of IPR disclosures made to the IETF Secretariat and any 1313 assurances of licenses to be made available, or the result of an 1314 attempt made to obtain a general license or permission for the use of 1315 such proprietary rights by implementers or users of this 1316 specification can be obtained from the IETF on-line IPR repository at 1317 http://www.ietf.org/ipr. 1319 The IETF invites any interested party to bring to its attention any 1320 copyrights, patents or patent applications, or other proprietary 1321 rights that may cover technology that may be required to implement 1322 this standard. Please address the information to the IETF at 1323 ietf-ipr@ietf.org. 1325 Acknowledgment 1327 Funding for the RFC Editor function is provided by the IETF 1328 Administrative Support Activity (IASA).