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1 SIPPING J. Rosenberg
2 Internet-Draft Cisco Systems
3 Expires: May 5, 2005 H. Schulzrinne
4 Columbia University
5 R. Mahy, Ed.
6 Airespace
7 Nov 4, 2004
9 An INVITE Inititiated Dialog Event Package for the Session
10 Initiation Protocol (SIP)
11 draft-ietf-sipping-dialog-package-05.txt
13 Status of this Memo
15 This document is an Internet-Draft and is subject to all provisions
16 of section 3 of RFC 3667. By submitting this Internet-Draft, each
17 author represents that any applicable patent or other IPR claims of
18 which he or she is aware have been or will be disclosed, and any of
19 which he or she become aware will be disclosed, in accordance with
20 RFC 3668.
22 Internet-Drafts are working documents of the Internet Engineering
23 Task Force (IETF), its areas, and its working groups. Note that
24 other groups may also distribute working documents as
25 Internet-Drafts.
27 Internet-Drafts are draft documents valid for a maximum of six months
28 and may be updated, replaced, or obsoleted by other documents at any
29 time. It is inappropriate to use Internet-Drafts as reference
30 material or to cite them other than as "work in progress."
32 The list of current Internet-Drafts can be accessed at
33 http://www.ietf.org/ietf/1id-abstracts.txt.
35 The list of Internet-Draft Shadow Directories can be accessed at
36 http://www.ietf.org/shadow.html.
38 This Internet-Draft will expire on May 5, 2005.
40 Copyright Notice
42 Copyright (C) The Internet Society (2004).
44 Abstract
46 This document defines a dialog event package for the SIP Events
47 architecture, along with a data format used in notifications for this
48 package. The dialog package allows users to subscribe to another
49 user, an receive notifications about the changes in state of INVITE
50 initiated dialogs that the user is involved in.
52 Table of Contents
54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
55 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
56 3. Dialog Event Package . . . . . . . . . . . . . . . . . . . . . 5
57 3.1 Event Package Name . . . . . . . . . . . . . . . . . . . . 5
58 3.2 Event Package Parameters . . . . . . . . . . . . . . . . . 5
59 3.3 SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . . 6
60 3.4 Subscription Duration . . . . . . . . . . . . . . . . . . 7
61 3.5 NOTIFY Bodies . . . . . . . . . . . . . . . . . . . . . . 7
62 3.6 Notifier Processing of SUBSCRIBE Requests . . . . . . . . 7
63 3.7 Notifier Generation of NOTIFY Requests . . . . . . . . . . 8
64 3.7.1 The Dialog State Machine . . . . . . . . . . . . . . . 9
65 3.7.2 Applying the state machine . . . . . . . . . . . . . . 12
66 3.8 Subscriber Processing of NOTIFY Requests . . . . . . . . . 13
67 3.9 Handling of Forked Requests . . . . . . . . . . . . . . . 13
68 3.10 Rate of Notifications . . . . . . . . . . . . . . . . . . 14
69 3.11 State Agents . . . . . . . . . . . . . . . . . . . . . . . 14
70 4. Dialog Information Format . . . . . . . . . . . . . . . . . . 14
71 4.1 Structure of Dialog Information . . . . . . . . . . . . . 14
72 4.1.1 Dialog Element . . . . . . . . . . . . . . . . . . . . 15
73 4.1.2 State . . . . . . . . . . . . . . . . . . . . . . . . 16
74 4.1.3 Duration . . . . . . . . . . . . . . . . . . . . . . . 16
75 4.1.4 Replaces . . . . . . . . . . . . . . . . . . . . . . . 16
76 4.1.5 Referred-By . . . . . . . . . . . . . . . . . . . . . 17
77 4.1.6 Local and Remote elements . . . . . . . . . . . . . . 17
78 4.1.6.1 Identity . . . . . . . . . . . . . . . . . . . . . 17
79 4.1.6.2 Target . . . . . . . . . . . . . . . . . . . . . . 17
80 4.1.6.3 Session Description . . . . . . . . . . . . . . . 18
81 4.2 Sample Notification Body . . . . . . . . . . . . . . . . . 19
82 4.3 Constructing Coherent State . . . . . . . . . . . . . . . 19
83 4.4 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 20
84 5. Definition of new media feature parameters . . . . . . . . . . 23
85 5.1 The "sip.byeless" parameter . . . . . . . . . . . . . . . 23
86 5.2 The "sip.rendering" parameter . . . . . . . . . . . . . . 24
87 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
88 6.1 Basic Example . . . . . . . . . . . . . . . . . . . . . . 24
89 6.2 Emulating a Shared-Line phone system . . . . . . . . . . . 27
90 6.3 Minimal Dialog Information with Privacy . . . . . . . . . 31
91 7. Security Considerations . . . . . . . . . . . . . . . . . . . 32
92 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
93 8.1 application/dialog-info+xml MIME Registration . . . . . . 33
94 8.2 URN Sub-Namespace Registration for
95 urn:ietf:params:xml:ns:dialog-info . . . . . . . . . . . . 33
96 8.3 Schema Registration . . . . . . . . . . . . . . . . . . . 34
97 8.4 Media Feature Parameter Registration . . . . . . . . . . . 34
98 8.4.1 sip.byeless . . . . . . . . . . . . . . . . . . . . . 34
99 8.4.2 sip.rendering . . . . . . . . . . . . . . . . . . . . 35
100 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 36
101 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
102 10.1 Normative References . . . . . . . . . . . . . . . . . . . . 36
103 10.2 Informative References . . . . . . . . . . . . . . . . . . . 37
104 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 37
105 Intellectual Property and Copyright Statements . . . . . . . . 39
107 1. Introduction
109 The SIP Events framework [1] defines general mechanisms for
110 subscription to, and notification of, events within SIP networks. It
111 introduces the notion of a package, which is a specific
112 "instantiation" of the events mechanism for a well-defined set of
113 events. Packages have been defined for user presence [16], watcher
114 information [17], and message waiting indicators [18], amongst
115 others. Here, we define an event package for INVITE initiated
116 dialogs. Dialogs refer to the SIP relationship established between
117 two SIP peers [2]. Dialogs can be created by many methods, although
118 RFC 3261 defines only one - the INVITE method. RFC 3265 defines the
119 SUBSCRIBE and NOTIFY methods, which also create dialogs. However,
120 the usage of this package to model transitions in the state of those
121 dialogs is out of the scope of this specification.
123 There are a variety of applications enabled through the knowledge of
124 INVITE dialog state. Some examples include:
125 Automatic Callback: In this basic Public Switched Telephone Network
126 (PSTN) application, user A calls user B. User B is busy. User A
127 would like to get a callback when user B hangs up. When B hangs
128 up, user A's phone rings. When A picks it up, they here ringing,
129 and are being connected to B. To implement this with SIP, a
130 mechanism is required for B to receive a notification when the
131 dialogs at A are complete.
132 Presence-Enabled Conferencing: In this application, a user A wishes
133 to set up a conference call with users B and C. Rather than
134 scheduling it, it is to be created automatically when A, B and C
135 are all available. To do this, the server providing the
136 application would like to know whether A, B and C are "online",
137 not idle, and not in a phone call. Determining whether or not A,
138 B and C are in calls can be done in two ways. In the first, the
139 server acts as a call stateful proxy for users A, B and C, and
140 therefore knows their call state. This won't always be possible,
141 however, and it introduces scalability, reliability, and
142 operational complexities. Rather, the server would subscribe to
143 the dialog state of those users, and receive notifications as it
144 changes. This enables the application to be provided in a
145 distributed way; the server need not reside in the same domain as
146 the users.
147 IM Conference Alerts: In this application, a user can get an Instant
148 Message (IM) sent to their phone whenever someone joins a
149 conference that the phone is involved in. The IM alerts are
150 generated by an application separate from the conference server.
152 In general, the dialog package allows for construction of distributed
153 applications, where the application requires information on dialog
154 state, but is not co-resident with the end user on which that state
155 resides.
157 In addition, this document also defines two new callee capabilities
158 [10] feature parameters: "sip.byeless", which indicates that a SIP
159 User Agent (UA) is not capable of terminating a session itself (for
160 example as with some announcement or recording services, and in some
161 call centers)in which the UA is no longer interested in
162 participating; and "sip.rendering", which positively describes if the
163 User Agent is rendering any of the media it is receiving.
165 2. Terminology
167 In this document, the key words "MUST", "MUST NOT", "REQUIRED",
168 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
169 and "OPTIONAL" are to be interpreted as described in RFC 2119 [9] and
170 indicate requirement levels for compliant implementations.
172 3. Dialog Event Package
174 This section provides the details for defining a SIP Events package,
175 as specified by [1].
177 3.1 Event Package Name
179 The name of this event package is "dialog". This package name is
180 carried in the Event and Allow-Events header, as defined in [1].
182 3.2 Event Package Parameters
184 This package defines four Event Package parameters. They are
185 call-id, to-tag, from-tag, and include-session-description. If a
186 subscription to a specific dialog is requested, all of the first
187 three of these parameters MUST be present. They identify the dialog
188 that is being subscribed to. The to-tag is matched against the local
189 tag, the from-tag is matched against the remote tag, and the call-id
190 is matched against the Call-ID. The include-session-description
191 parameter indicates if the subscriber would like to receive the
192 session descriptions associated with the subscribed dialog or
193 dialogs.
195 It is also possible to subscribe to the set of dialogs created as a
196 result of a single INVITE sent by a UAC. In that case, the call-id
197 and to-tag MUST be present. The to-tag is matched against the local
198 tag, and the call-id is matched against the Call-ID.
200 The ABNF for these parameters is shown below. It refers to many
201 constructions from the ABNF of RFC3261, such as EQUAL, DQUOTE, and
202 token.
204 call-id = "call-id" EQUAL ( token / DQUOTE callid DQUOTE )
205 ;; NOTE: any DQUOTEs inside callid MUST be escaped!
206 from-tag = "from-tag" EQUAL token
207 to-tag = "to-tag" EQUAL token
208 with-sessd = "include-session-description"
210 Any callids which contain embedded double-quotes MUST escape those
211 double-quotes using the backslash-quoting mechanism. Note that the
212 call-id parameter may need to be expressed as a quoted string. This
213 is because the ABNF for callid and word (which is used by callid)
214 allow for some characters (such as "@", "[", and ":") which are not
215 allowed within a token.
217 3.3 SUBSCRIBE Bodies
219 A SUBSCRIBE for a dialog package MAY contain a body. This body
220 defines a filter to apply to the subscription. Filter documents are
221 not specified in this document, and at the time of writing, are
222 expected to be the subject of future standardization activity.
224 A SUBSCRIBE for a dialog package MAY be sent without a body. This
225 implies the default subscription filtering policy. The default
226 policy is:
227 o If the Event header field contained dialog identifiers,
228 notifications are generated every time there is a change in the
229 state of any matching dialogs for the user identified in the
230 request URI of the SUBSCRIBE.
231 o If there were no dialog identifiers in the Event header field,
232 notifications are generated every time there is any change in the
233 state of any dialogs for the user identified in the request URI of
234 the SUBSCRIBE with the following exceptions. If the target
235 (Contact) URI of a subscriber is equivalent to the remote target
236 URI of a specific dialog, then the dialog element for that dialog
237 is suppressed for that subscriber. (The subscriber is already a
238 party in the dialog directly, so these notifications are
239 superfluous.) If no dialogs remain after supressing dialogs, the
240 entire notification to that subscriber is supressed and the
241 version number in the dialog-info element is not incremented for
242 that subscriber. Implicit filtering for one subscriber does not
243 affect notifications to other subscribers.
244 o Notifications do not normally contain full state; rather, they
245 only indicate the state of the dialog whose state has changed.
246 The exceptions are a NOTIFY sent in response to a SUBSCRIBE, and a
247 NOTIFY that contains no dialog elements. These NOTIFYs contain
248 the complete view of dialog state.
249 o The notifications contain the identities of the participants in
250 the dialog, the target URIs, and the dialog identifiers. Session
251 descriptions are not included normally unless explicitly requested
252 and/or explicitly authorized.
254 3.4 Subscription Duration
256 Dialog state changes fairly quickly; once established, a typical
257 phone call lasts a few minutes (this is different for other session
258 types, of course). However, the interval between new calls is
259 typically infrequent. As such, we arbitrarily choose a default
260 duration of one hour. Clients SHOULD specify an explicit duration.
262 There are two distinct use cases for dialog state. The first is when
263 a subscriber is interested in the state of a specific dialog or
264 dialogs (and they are authorized to find out about just the state of
265 those dialogs). In that case, when the dialogs terminate, so too
266 does the subscription. In these cases, the value of the subscription
267 duration is largely irrelevant, and SHOULD be longer than the typical
268 duration of a dialog, about two hours would cover most dialogs.
270 In another case, a subscriber is interested in the state of all
271 dialogs for a specific user. In these cases, a shorter interval
272 makes more sense. The default is one hour for these subscriptions.
274 3.5 NOTIFY Bodies
276 As described in RFC 3265 [1], the NOTIFY message will contain bodies
277 that describe the state of the subscribed resource. This body is in
278 a format listed in the Accept header field of the SUBSCRIBE, or a
279 package-specific default if the Accept header field was omitted from
280 the SUBSCRIBE.
282 In this event package, the body of the notification contains a dialog
283 information document. This document describes the state of one or
284 more dialogs associated with the subscribed resource. All
285 subscribers and notifiers MUST support the
286 "application/dialog-info+xml" data format described in Section 4.
287 The subscribe request MAY contain an Accept header field. If no such
288 header field is present, it has a default value of
289 "application/dialog-info+xml". If the header field is present, it
290 MUST include "application/dialog-info+xml", and MAY include any other
291 types capable of representing dialog state.
293 Of course, the notifications generated by the server MUST be in one
294 of the formats specified in the Accept header field in the SUBSCRIBE
295 request.
297 3.6 Notifier Processing of SUBSCRIBE Requests
299 The dialog information for a user contains sensitive information.
301 Therefore, all subscriptions SHOULD be authenticated and then
302 authorized before approval. All implementors of this package MUST
303 support the digest authentication mechanism as a baseline.
304 Authorization policy is at the discretion of the administrator, as
305 always. However, a few recommendations can be made.
307 It is RECOMMENDED that, if the policy of user B is that user A is
308 allowed to call them, dialog subscriptions from user A be allowed.
309 However, the information provided in the notifications does not
310 contain any dialog identification information; merely an indication
311 of whether the user is in at least one call, or not. Specifically,
312 they should not be able to find out any more information than if they
313 sent an INVITE. (This concept of a "virtual" dialog is discussed
314 more in Section 3.7.2, and an example of such a notification body is
315 shown below.)
316
317
320
323
325 It is RECOMMENDED that if a user agent registers with the
326 address-of-record X, that this user agent authorize subscriptions
327 that come from any entity that can authenticate itself as X.
328 Complete information on the dialog state SHOULD be sent in this case.
329 This authorization behavior allows a group of devices representing a
330 single user to all become aware of each other's state. This is
331 useful for applications such as single-line-extension.
332 Note that many implementations of "shared-lines" have a feature
333 which allows details of calls on a shared address-of-record to be
334 made private. This is a completely reasonable authorization
335 policy which could result in notifications which contain only the
336 id attribute of the dialog element and the state element when
337 shared-line privacy is requested, and notifications with more
338 complete information when shared-line privacy is not requested.
340 3.7 Notifier Generation of NOTIFY Requests
342 Notifications are generated for the dialog package when an INVITE
343 request is sent, when a new dialog comes into existence at a UA, or
344 when the state or characteristics of an existing dialog changes.
345 Therefore, a model of dialog state is needed in order to determine
346 precisely when to send notifications, and what their content should
347 be. The SIP specification has a reasonably well defined lifecycle
348 for dialogs. However, it is not explicitly modelled. This
349 specification provides an explicit model of dialog state through a
350 finite state machine.
352 It is RECOMMENDED that NOTIFY requests only contain information on
353 the dialogs whose state or participation information has changed.
354 However, if a notifier receives a SUBSCRIBE request, the triggered
355 NOTIFY SHOULD contain the state of all dialogs that the subscriber is
356 authorized to see.
358 3.7.1 The Dialog State Machine
360 Modelling of dialog state is complicated by two factors. The first
361 is forking, which can cause a single INVITE to generate many dialogs
362 at a UAC. The second is the differing views of state at the UAC and
363 UAS. We have chosen to handle the first issue by extending the
364 dialog FSM to include the states between transmission of the INVITE
365 and the creation of actual dialogs through receipt of 1xx and 2xx
366 responses. As a result, this specification supports the notion of
367 dialog state for dialogs before they are fully instantiated.
369 We have also chosen to use a single FSM for both UAC and UAS.
371 +----------+ +----------+
372 | | 1xx-notag | |
373 | |----------->| |
374 | Trying | |Proceeding|-----+
375 | |---+ +-----| | |
376 | | | | | | |
377 +----------+ | | +----------+ |
378 | | | | | |
379 | | | | | |
380 +<--C-----C--+ |1xx-tag |
381 | | | | |
382 cancelled| | | V |
383 rejected| | |1xx-tag +----------+ |
384 | | +------->| | |2xx
385 | | | | |
386 +<--C--------------| Early |-----C---+ 1xx-tag
387 | | replaced | | | | w/new tag
388 | | | |<----C---+ (new FSM
389 | | +----------+ | instance
390 | | 2xx | | created)
391 | +----------------+ | |
392 | | |2xx |
393 | | | |
394 V V V |
395 +----------+ +----------+ |
396 | | | | |
397 | | | | |
398 |Terminated|<-----------| Confirmed|<----+
399 | | error | |
400 | | timeout | |
401 +----------+ replaced +----------+
402 local-bye | ^
403 remote-bye | |
404 | |
405 +------+
406 2xx w. new tag
407 (new FSM instance
408 created)
410 Figure 3
412 The FSM for dialog state is shown in Figure 3. The FSM is best
413 understood by considering the UAC and UAS cases separately.
415 The FSM is created in the "trying" state when the UAC sends an INVITE
416 request. Upon receipt of a 1xx without a tag, the FSM transitions to
417 the "proceeding" state. Note that there is no actual dialog yet, as
418 defined by the SIP specification. However, there is a "half-dialog",
419 in the sense that two of the three components of the dialog ID are
420 known (the call identifier and local tag). If a 1xx with a tag is
421 received, the FSM transitions to the early state. The full dialog
422 identifier is now defined. Had a 2xx been received, the FSM would
423 have transitioned to the "confirmed" state.
425 If, after transitioning to the "early" or "confirmed" states, the UAC
426 receives another 1xx or 2xx respectively with a different tag,
427 another instance of the FSM is created, initialized into the "early"
428 or "confirmed" state respectively. The benefit of this approach is
429 that there will be a single FSM representing the entire state of the
430 invitation and resulting dialog when dealing with the common case of
431 no forking.
433 If the UAC should send a CANCEL, and then subsequently receive a 487
434 to its INVITE transaction, all FSMs spawned from that INVITE
435 transition to the "terminated" state with the event "cancelled". If
436 the UAC receives a new invitation (with a Replaces [13] header) which
437 replaces the current Early or Confirmed dialog, all INVITE
438 transactions spawned from the replaced invitation transition to the
439 "terminated" state with the event "replaced". If the INVITE
440 transaction terminates with a non-2xx response for any other reason,
441 all FSMs spawned from that INVITE transition to the terminated state
442 with the event "rejected".
444 Once in the confirmed state, the call is active. It can transition
445 to the terminated state if the UAC sends a BYE or receives a BYE
446 (corresponding to the "local-bye" and "remote-bye" events as
447 appropriate), if a mid-dialog request generates a 481 or 408 response
448 (corresponding to the "error" event), or a mid-dialog request
449 generates no response (corresponding to the "timeout" event).
451 From the perspective of the UAS, when an INVITE is received, the FSM
452 is created in the "trying" state. If it sends a 1xx without a tag,
453 the FSM transitions to the "proceeding" state. If a 1xx is sent with
454 a tag, the FSM transitions to the "early" state, and if a 2xx is
455 sent, it transitions to the "confirmed" state. If the UAS should
456 receive a CANCEL request and then generate a 487 response to the
457 INVITE (which can occur in the proceeding and early states), the FSM
458 transitions to the terminated state with the event "cancelled". If
459 the UAS should generate any other non-2xx final response to the
460 INVITE request, the FSM transitions to the terminated state with the
461 event "rejected". If the UAS receives a new invitation (with a
462 Replaces [13] header) which replaces the current Confirmed dialog,
463 the replaced invitation transition transitions to the "terminated"
464 state with the event "replaced". Once in the "confirmed" state, the
465 other transitions to the "terminated" state occur for the same
466 reasons they do in the case of UAC.
468 There should never be a transition from the "trying" state to the
469 "terminated" state with the event "cancelled", since the SIP
470 specification prohibits transmission of CANCEL until a provisional
471 response is received. However, this transition is defined in the
472 FSM just to unify the transitions from trying, proceeding, and
473 early to the terminated state.
475 3.7.2 Applying the state machine
477 The notifier MAY generate a NOTIFY request on any event transition of
478 the FSM. Whether it does or not is policy dependent. However, some
479 general guidelines are provided.
481 When the subscriber is unauthenticated, or is authenticated, but
482 represents a third party with no specific authorization policies, it
483 is RECOMMENDED that subscriptions to an individual dialog, or to a
484 specific set of dialogs, is forbidden. Only subscriptions to all
485 dialogs (i.e., there are no dialog identifiers in the Event header
486 field) are permitted. In that case, actual dialog states across all
487 dialogs will not be reported. Rather, a single "virtual" dialog FSM
488 be used, and event transitions on that FSM be reported.
490 If there is any dialog at the UA whose state is "confirmed", the
491 virtual FSM is in the "confirmed" state. If there are no dialogs at
492 the UA in the confirmed state, but there is at least one in the
493 "early" state, the virtual FSM is in the "early" or "confirmed"
494 state. If there are no dialogs in the confirmed or early states, but
495 there is at least one in the "proceeding" state, the virtual FSM is
496 in the "proceeding", "early" or "confirmed" state. If there are no
497 dialogs in the confirmed, early, or proceeding states, but there is
498 at least one in the "trying" state, the virtual FSM is in the
499 "trying", "proceeding", "early" or "confirmed" state. The choice
500 about which state to use depends on whether the UA wishes to let
501 unknown users know that their phone is ringing, as opposed to in an
502 active call.
504 It is RECOMMENDED that, in the absence of any preference, "confirmed"
505 is used in all cases (as shown in the example in Section 3.6.
506 Furthermore, it is RECOMMENDED that the notifications of changes in
507 the virtual FSM machine not convey any information except the state
508 of the FSM and its event transitions - no dialog identifiers (which
509 are ill-defined in this model in any case). The use of this virtual
510 FSM allows for minimal information to be conveyed. A subscriber
511 cannot know how many calls are in progress, or with whom, just that
512 there exists a call. This is the same information they would receive
513 if they simply sent an INVITE to the user instead; a 486 response
514 would indicate that they are on a call.
516 When the subscriber is authenticated, and has authenticated itself
517 with the same address-of-record that the UA itself uses, if no
518 explicit authorization policy is defined, it is RECOMMENDED that all
519 state transitions on dialogs that have been subscribed to (which is
520 either all of them, if no dialog identifiers were present in the
521 Event header field, or a specific set of them identified by the Event
522 header field parameters) be reported, along with complete dialog IDs.
524 The notifier SHOULD generate a NOTIFY request on any change in the
525 characteristics associated with the dialog. Since these include
526 Contact URIs, Contact parameters and session descriptions, receipt of
527 re-INVITEs and UPDATE requests [3] which modify this information MAY
528 trigger notifications.
530 3.8 Subscriber Processing of NOTIFY Requests
532 The SIP Events framework expects packages to specify how a subscriber
533 processes NOTIFY requests in any package specific ways, and in
534 particular, how it uses the NOTIFY requests to contruct a coherent
535 view of the state of the subscribed resource.
537 Typically, the NOTIFY for the dialog package will only contain
538 information about those dialogs whose state has changed. To
539 construct a coherent view of the total state of all dialogs, a
540 subscriber to the dialog package will need to combine NOTIFYs
541 received over time.
543 Notifications within this package can convey partial information;
544 that is, they can indicate information about a subset of the state
545 associated with the subscription. This means that an explicit
546 algorithm needs to be defined in order to construct coherent and
547 consistent state. The details of this mechanism are specific to the
548 particular document type. See Section 4.3 for information on
549 constructing coherent information from an application/dialog-info+xml
550 document.
552 3.9 Handling of Forked Requests
554 Since dialog state is distributed across the UA for a particular
555 user, it is reasonable and useful for a SUBSCRIBE request for dialog
556 state to fork, and reach multiple UA.
558 As a result, a forked SUBSCRIBE request for dialog state can install
559 multiple subscriptions. Subscribers to this package MUST be prepared
560 to install subscription state for each NOTIFY generated as a result
561 of a single SUBSCRIBE.
563 3.10 Rate of Notifications
565 For reasons of congestion control, it is important that the rate of
566 notifications not become excessive. As a result, it is RECOMMENDED
567 that the server not generate notifications for a single subscriber at
568 a rate faster than once every 1 second.
570 3.11 State Agents
572 Dialog state is ideally maintained in the user agents in which the
573 dialog resides. Therefore, the elements that maintain the dialog are
574 the ones best suited to handle subscriptions to it. However, in some
575 cases, a network agent may also know the state of the dialogs held by
576 a user. As such, state agents MAY be used with this package.
578 4. Dialog Information Format
580 Dialog information is an XML document [4] that MUST be well-formed
581 and SHOULD be valid. Dialog information documents MUST be based on
582 XML 1.0 and MUST be encoded using UTF-8. This specification makes
583 use of XML namespaces for identifying dialog information documents
584 and document fragments. The namespace URI for elements defined by
585 this specification is a URN [5], using the namespace identifier
586 'ietf' defined by [6] and extended by [7]. This URN is:
588 urn:ietf:params:xml:ns:dialog-info
590 A dialog information document begins with the root element tag
591 "dialog-info".
593 4.1 Structure of Dialog Information
595 A dialog information document starts with a dialog-info element.
596 This element has three mandatory attributes:
597 version: This attribute allows the recipient of dialog information
598 documents to properly order them. Versions start at 0, and
599 increment by one for each new document sent to a subscriber.
600 Versions are scoped within a subscription. Versions MUST be
601 representable using a 32 bit integer.
602 state: This attribute indicates whether the document contains the
603 full dialog information, or whether it contains only information
604 on those dialogs which have changed since the previous document
605 (partial).
606 entity: This attribute contains a URI that identifies the user whose
607 dialog information is reported in the remainder of the document.
608 This user is referred to as the "observed user".
610 The dialog-info element has a series of zero or more dialog
611 sub-elements. Each of those represents a specific dialog.
612
613
616
618 4.1.1 Dialog Element
620 The dialog element reports information on a specific dialog or
621 "half-dialog". It has single mandatory attribute: id. The id
622 attribute provides a single string that can be used as an identifier
623 for this dialog or "half-dialog". This is a different identifier
624 than the dialog ID defined in RFC 3261 [2], but related to it.
626 For a caller, the id is created when an INVITE request is sent. When
627 a 1xx with a tag, or a 2xx is received, the dialog is formally
628 created. The id remains unchanged. However, if an additional 1xx or
629 2xx is received, resulting in the creation of another dialog (and
630 resulting FSM), that dialog is allocated a new id.
632 For a callee, the id is created when an INVITE outside of an existing
633 dialog is received. When a 2xx or a 1xx with a tag is sent, creating
634 the dialog, the id remains unchanged.
636 The id MUST be unique amongst all dialogs at a UA.
638 There are a number of optional attributes which provide
639 identification information about the dialog:
640 call-id: This attribute is a string which represents the call-id
641 component of the dialog identifier. (Note that single and double
642 quotes inside a call-id must be escaped using "e; for " and
643 ' for ' .)
644 local-tag: This attribute is a string which represents the local-tag
645 component of the dialog identifier.
646 remote-tag: This attribute is a string which represents the
647 remote-tag component of the dialog identifier. The remote tag
648 attribute won't be present if there is only a "half-dialog",
649 resulting from the generation of an INVITE for which no final
650 responses or provisional responses with tags has been received.
651 direction: This attribute is either initiator or recipient, and
652 indicates whether the observed user was the initiator of the
653 dialog, or the recipient of the INVITE that created it.
655
656
659
663
665 The sub-elements of the dialog element provide additional information
666 about the dialog. Some of these sub-elements provide more detail
667 about the dialog itself, while the local and remote sub-elements
668 describe characteristics of the participants involved in the dialog.
669 The only mandatory sub-element is the state element.
671 4.1.2 State
673 The state element indicates the state of the dialog. Its value is an
674 enumerated type describing one of the states in the FSM above. It
675 has an optional event attribute that can be used to indicate the
676 event which caused any transition into the terminated state, and an
677 optional code attribute that indicates the response code associated
678 with any transition caused by a response to the original INVITE.
680 terminated
682 4.1.3 Duration
684 The duration element contains the amount of time, in seconds, since
685 the FSM was created.
687 145
689 4.1.4 Replaces
691 The replaces element is used to correlate a new dialog with one it
692 replaced as a result of an invitation with a Replaces header. This
693 element is present in the replacement dialog only (the newer dialog)
694 and contains attributes with the call-id, local-tag, and remote-tag
695 of the replaced dialog.
697
700 4.1.5 Referred-By
702 The referred-by element is used to correlate a new dialog with a
703 REFER [12] request which triggered it. The element is present in a
704 dialog which was triggered by a REFER request which contained a
705 Referred-By [11] header and contains the (optional) display name
706 attribute and the Referred-By URI as its value.
708 sip:bob@example.com
710 4.1.6 Local and Remote elements
712 The local and remote elements are sub-elements of the dialog element
713 which contain information about the local and remote participants
714 respectively. They both have a number of optional sub-elements which
715 indicate the identity conveyed by the participant, the target URI,
716 the feature-tags of the target, and the session-description of the
717 participant.
719 4.1.6.1 Identity
721 The identity element indicates a local or remote URI, as defined in
722 [2] as appropriate. It has an optional attribute, display, that
723 contains the display name from the appropriate URI.
724 Note that multiple identities (for example a sip: URI and a tel:
725 URI) could be included if they all correspond to the participant.
726 To avoid repeating identity information in each request, the
727 subscriber can assume that the identity URIs are the same as in
728 previous notifications if no identity elements are present in the
729 corresponding local or remote element. If any identity elements
730 are present in the local or remote part of a notification, the new
731 list of identity tags completely supersedes the old list in the
732 corresponding part.
734
735 sip:anonymous@anonymous.invalid
737 4.1.6.2 Target
739 The target contains the local or remote target URI as constructed by
740 the user agent for this dialog, as defined in RFC 3261 [2] in a "uri"
741 attribute.
743 It can contain a list of Contact header parameters in param
744 sub-elements (such as those defined in [10]. The param element
745 contains two required attributes, pname and pval. (Boolean
746 parameters are represented by the explicit pval values "true" and
747 "false" [for example when a feature parameter is explicitly
748 negated]). The param element itself has no contents. To avoid
749 repeating Contact information in each request, the subscriber can
750 assume that the target URI and parameters are the same as in previous
751 notifications if no target element is present in the corresponding
752 local or remote element. If a target element is present in the local
753 or remote part of a notification, the new target tag and list of an
754 parameter tags completely supersedes the old target and parameter
755 list in the corresponding part.
757
758
759
760
762 4.1.6.3 Session Description
764 The session-description element contains the session description used
765 by the observed user for its end of the dialog. This element should
766 generally NOT be included in the notifications, unless explicitly
767 requested by the subscriber. It has a single attribute, type, which
768 indicates the MIME media type of the session description. To avoid
769 repeating session description information in each request, the
770 subscriber can assume that the session description is the same as in
771 previous notifications if no session description element is present
772 in the corresponding local or remote element.
774 4.2 Sample Notification Body
776
777
781
796
798 4.3 Constructing Coherent State
800 The dialog information subscriber maintains a table for the list of
801 dialogs. The table contains a row for each dialog. Each row is
802 indexed by an ID, present in the "id" attribute of the "dialog"
803 element. The contents of each row contain the state of that dialog
804 as conveyed in the document. The table is also associated with a
805 version number. The version number MUST be initialized with the
806 value of the "version" attribute from the "dialog-info" element in
807 the first document received. Each time a new document is received,
808 the value of the local version number, and the "version" attribute in
809 the new document, are compared. If the value in the new document is
810 one higher than the local version number, the local version number is
811 increased by one, and the document is processed. If the value in the
812 document is more than one higher than the local version number, the
813 local version number is set to the value in the new document, and the
814 document is processed. If the document did not contain full state,
815 the subscriber SHOULD generate a refresh request to trigger a full
816 state notification. If the value in the document is less than the
817 local version, the document is discarded without processing.
819 The processing of the dialog information document depends on whether
820 it contains full or partial state. If it contains full state,
821 indicated by the value of the "state" attribute in the "dialog-info"
822 element, the contents of the table are flushed. They are repopulated
823 from the document. A new row in the table is created for each
824 "dialog" element. If the document contains partial state, as
825 indicated by the value of the "state" attribute in the "dialog-info"
826 element, the document is used to update the table. For each "dialog"
827 element in the document, the subscriber checks to see whether a row
828 exists for that dialog. This check is done by comparing the ID in
829 the "id" attribute of the "dialog" element with the ID associated
830 with the row. If the dialog doesn't exist in the table, a row is
831 added, and its state is set to the information from that "dialog"
832 element. If the dialog does exist, its state is updated to be the
833 information from that "dialog" element. If a row is updated or
834 created, such that its state is now terminated, that entry MAY be
835 removed from the table at any time.
837 4.4 Schema
839 The following is the schema for the application/dialog-info+xml type:
841
842
848
849
851
852
853
854
856
858
859
861
862
863
864
865
866
867
869
870
871
872
873
874
875
876
877
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881
883
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899
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913
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917
918
919
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921
922
923
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927
928
929
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932
933
935
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938
939
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941
942
943
945
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949
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961
962
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964
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971
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975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
998 5. Definition of new media feature parameters
1000 5.1 The "sip.byeless" parameter
1002 The "sip.byeless" media feature parameter is a new boolean parameter,
1003 defined in this document, which provides a positive indication that
1004 the User Agent setting the parameter is unable to terminate sessions
1005 on its own (for example, by sending a BYE request). For example,
1006 continuous announcement services and certain recording services are
1007 unable to determine when it would be desirable to terminate a session
1008 and therefore do not have the ability to terminate sessions at all.
1009 Also, many human call centers are configured so that they never
1010 terminate sessions. (This is to prevent call center agents from
1011 accidentally disconnecting the caller.)
1012 Contact:
1013 ;automaton;+sip.byeless
1015 5.2 The "sip.rendering" parameter
1017 The "sip.rendering" media feature parameter is a new string
1018 parameter, defined in this document, which can provide a positive
1019 indication whether the User Agent setting the parameter is currently
1020 rendering any of the media it is receiving in the context of a
1021 specific session. It MUST only be used in a Contact header field in
1022 a dialog created using the INVITE request. (Note that per [10] this
1023 parameter name must be preceeded by a "+" character when used in a
1024 SIP Contact header field.)
1026 This parameter has three legal values: "yes", "no", and "unknown".
1027 The value "yes" indicates positive knowledge that the User Agent is
1028 rendering at least one of the streams of media that it is receiving.
1029 The value "no" indicates positive knowledge that the User Agent is
1030 rendering none of the media that it is receiving. The value
1031 "unknown" indicates that the User Agent does not know whether the
1032 media associated with the session is being rendered. (which may be
1033 the case if the User Agent is acting as a 3pcc (Third Party Call
1034 Control) [19] controller).
1036 The "sip.rendering" parameter is useful in applications such as
1037 shared appearances, conference status monitoring, or as an input to
1038 user presence.
1040 Contact:
1041 ;automaton;+sip.rendering="no"
1043 6. Examples
1045 6.1 Basic Example
1047 For example, if a UAC sends an INVITE that looks like, in part:
1049 INVITE sip:bob@example.com SIP/2.0
1050 Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8
1051 Max-Forwards: 70
1052 To: Bob
1053 From: Alice ;tag=1928301774
1054 Call-ID: a84b4c76e66710
1055 CSeq: 314159 INVITE
1056 Contact:
1057 Content-Type: application/sdp
1058 Content-Length: 142
1060 [SDP not shown]
1062 The XML document in a notification from Alice might look like:
1064
1065
1069
1073
1075 If the following 180 response is received:
1077 SIP/2.0 180 Ringing
1078 Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8
1079 To: Bob ;tag=456887766
1080 From: Alice ;tag=1928301774
1081 Call-ID: a84b4c76e66710
1082 CSeq: 314159 INVITE
1083 Contact:
1085 The XML document in a notification might look like:
1087
1088
1092
1097
1099 If it receives a second 180 with a different tag:
1101 SIP/2.0 180 Ringing
1102 Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8
1103 To: Bob ;tag=hh76a
1104 From: Alice ;tag=1928301774
1105 Call-ID: a84b4c76e66710
1106 CSeq: 314159 INVITE
1107 Contact:
1109 This results in the creation of a second dialog:
1111
1112
1116
1121
1126
1128 If a 200 OK is received on the second dialog, it moves to confirmed:
1130
1131
1135
1140
1142 32 seconds later, the other early dialog terminates because no 2xx is
1143 received for it. This implies that it was successfully cancelled,
1144 and therefore the following notification is sent:
1146
1147
1151
1156
1158 6.2 Emulating a Shared-Line phone system
1160 The following example shows how a SIP telephone user agent can
1161 provide detailed state information and also emulate a shared-line
1162 telephone system (the phone "lies" about having a dialog while it is
1163 merely offhook).
1165 Idle:
1167
1168
1171
1173 Seized:
1175
1176
1179
1182
1184 Dialing:
1186
1187
1190
1203
1205 Ringing:
1207
1208
1211
1219
1221 Answered (by voicemail):
1223
1224
1227
1232
1244
1246 Alice requests voicemail for Bob's attendant.
1247 (Alice presses "0" in North America / "9" in Europe)
1248 Voicemail completes a transfer with Cathy
1250
1251
1254
1259
1284
1286 Alice and Cathy talk, Cathy adds Alice to a local conference.
1288
1289
1292
1302
1304 Alice puts Cathy on hold
1306
1307
1310
1320
1321 Cathy hangs up
1323
1324
1327
1332
1335
1337 Alice hangs up:
1339
1340
1343
1345 6.3 Minimal Dialog Information with Privacy
1347 The following example shows the same user agent providing minimal
1348 information to maintain privacy for services like automatic callback.
1350 Onhook:
1352
1353
1356
1358 Offhook: (implementation/policy choice for Alice to transition
1359 to this "state" when "seized", when Trying, when Proceeding,
1360 or when Confirmed.)
1362
1363
1366
1369
1371 Onhook: (implementation/policy choice for Alice to transition to
1372 this "state" when terminated, or when no longer "seized")
1374
1375
1378
1380 7. Security Considerations
1382 Subscriptions to dialog state can reveal sensitive information. For
1383 this reason, Section 3.6 discusses authentication and authorization
1384 of subscriptions, and provides guidelines on sensible authorization
1385 policies. All implementations of this package MUST support the
1386 digest authentication mechanism.
1388 Since the data in notifications is sensitive as well, end-to-end SIP
1389 encryption mechanisms using S/MIME MAY be used to protect it. User
1390 Agents that implement the dialog package SHOULD also implement SIP
1391 over TLS [15] and the sips: scheme.
1393 8. IANA Considerations
1395 This document registers a new MIME type, application/dialog-info+xml;
1396 a new XML namespace; and two new media feature parameters in the SIP
1397 tree.
1399 8.1 application/dialog-info+xml MIME Registration
1400 MIME media type name: application
1401 MIME subtype name: dialog-info+xml
1402 Mandatory parameters: none
1403 Optional parameters: Same as charset parameter application/xml as
1404 specified in RFC 3023 [8].
1405 Encoding considerations: Same as encoding considerations of
1406 application/xml as specified in RFC 3023 [8].
1407 Security considerations: See Section 10 of RFC 3023 [8] and Section 7
1408 of this specification.
1409 Interoperability considerations: none.
1410 Published specification: This document.
1411 Applications which use this media type: This document type has been
1412 used to support SIP applications such as call return and
1413 auto-conference.
1414 Additional Information:
1415 Magic Number: None
1416 File Extension: .dif or .xml
1417 Macintosh file type code: "TEXT"
1418 Personal and email address for further information: Jonathan
1419 Rosenberg,
1420 Intended usage: COMMON
1421 Author/Change controller: The IETF.
1423 8.2 URN Sub-Namespace Registration for
1424 urn:ietf:params:xml:ns:dialog-info
1426 This section registers a new XML namespace, as per the guidelines in
1427 [7].
1428 URI: The URI for this namespace is
1429 urn:ietf:params:xml:ns:dialog-info.
1430 Registrant Contact: IETF, SIPPING working group, ,
1431 Jonathan Rosenberg .
1432 XML:
1434 BEGIN
1435
1436
1438
1439
1440
1442 Dialog Information Namespace
1443
1444
1445 Namespace for Dialog Information
1446 urn:ietf:params:xml:ns:dialog-info
1447 See RFCXXXX.
1448
1449
1450 END
1452 8.3 Schema Registration
1454 This specification registers a schema, as per the guidelines in in
1455 [7].
1456 URI: please assign.
1457 Registrant Contact: IETF, SIPPING Working Group
1458 (sipping@ietf.org), Jonathan Rosenberg (jdrosen@jdrosen.net).
1459 XML: The XML can be found as the sole content of Section 4.4.
1461 8.4 Media Feature Parameter Registration
1463 This section registers two new media feature tags, per the procedures
1464 defined in RFC 2506 [14]. The tags are placed into the sip tree,
1465 which is defined in [10].
1467 8.4.1 sip.byeless
1468 Media feature tag name sip.byeless
1469 ASN.1 Identifier New assignment by IANA.
1470 Summary of the media feature indicated by this tag This feature tag
1471 is a boolean flag. When set it indicates that the device is
1472 incapable of terminating a session autonomously.
1473 Values appropriate for use with this feature tag Boolean.
1474 The feature tag is intended primarily for use in the following
1475 applications, protocols, services, or negotiation mechanisms This
1476 feature tag is most useful in a communications application for
1477 describing the capabilities of an application, such as an
1478 announcement service, recording service, conference, or call
1479 center.
1481 Examples of typical use Call centers and media services.
1482 Related standards or documents RFC XXXX [[Note to IANA: Please
1483 replace XXXX with the RFC number of this specification.]]
1484 Security Considerations This media feature tag can be used in ways
1485 which affect application behaviors or may reveal private
1486 information. For example, a conferencing or other application may
1487 decide to terminate a call prematurely if this media feature tag
1488 is set. Therefore, if an attacker can modify the values of this
1489 tag, they may be able to affect the behavior of applications. As
1490 a result of this, applications which utilize this media feature
1491 tag SHOULD provide a means for ensuring its integrity. Similarly,
1492 this feature tag should only be trusted as valid when it comes
1493 from the user or user agent described by the tag. As a result,
1494 protocols for conveying this feature tag SHOULD provide a
1495 mechanism for guaranteeing authenticity.
1497 8.4.2 sip.rendering
1498 Media feature tag name sip.rendering
1499 ASN.1 Identifier New assignment by IANA.
1500 Summary of the media feature indicated by this tag This feature tag
1501 contains one of three string values indicating if the device is
1502 rendering any media from the current session ("yes"), none of the
1503 media from the current session ("no"), or if this status is not
1504 known to the device ("unknown").
1505 Values appropriate for use with this feature tag String.
1506 The feature tag is intended primarily for use in the following
1507 applications, protocols, services, or negotiation mechanisms This
1508 feature tag is most useful in a communications application, for
1509 describing the state of a device (such as a phone or PDA) during a
1510 multimedia session.
1511 Examples of typical use Conferencing, telephone shared-line
1512 emulation, and presence applications.
1513 Related standards or documents RFC XXXX [[Note to IANA: Please
1514 replace XXXX with the RFC number of this specification.]]
1515 Security Considerations This media feature tag can be used in ways
1516 which affect application behaviors or may reveal private
1517 information. For exmaple, a conferencing or other application may
1518 decide to terminate a call prematurely if this media feature tag
1519 is set to "no". Therefore, if an attacker can modify the values
1520 of this tag, they may be able to affect the behavior of
1521 applications. As a result of this, applications which utilize
1522 this media feature tag SHOULD provide a means for ensuring its
1523 integrity. Similarly, this feature tag should only be trusted as
1524 valid when it comes from the user or user agent described by the
1525 tag. As a result, protocols for conveying this feature tag SHOULD
1526 provide a mechanism for guaranteeing authenticity.
1528 9. Acknowledgements
1530 The authors would like to thank Sean Olson for his comments.
1532 10. References
1534 10.1 Normative References
1536 [1] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
1537 Notification", RFC 3265, June 2002.
1539 [2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
1540 Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
1541 Session Initiation Protocol", RFC 3261, June 2002.
1543 [3] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE
1544 Method", RFC 3311, October 2002.
1546 [4] Paoli, J., Sperberg-McQueen, C., Bray, T. and E. Maler,
1547 "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
1548 FirstEdition REC-xml-20001006, October 2000.
1550 [5] Moats, R., "URN Syntax", RFC 2141, May 1997.
1552 [6] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
1553 August 1999.
1555 [7] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
1556 January 2004.
1558 [8] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC
1559 3023, January 2001.
1561 [9] Bradner, S., "Key words for use in RFCs to Indicate Requirement
1562 Levels", BCP 14, RFC 2119, March 1997.
1564 [10] Rosenberg, J., Schulzrinne, H. and P. Kyzivat, "Indicating User
1565 Agent Capabilities in the Session Initiation Protocol (SIP)",
1566 RFC 3840, August 2004.
1568 [11] Sparks, R., "The Session Initiation Protocol (SIP) Referred-By
1569 Mechanism", RFC 3892, September 2004.
1571 [12] Sparks, R., "The Session Initiation Protocol (SIP) Refer
1572 Method", RFC 3515, April 2003.
1574 [13] Mahy, R., Biggs, B. and R. Dean, "The Session Initiation
1575 Protocol (SIP) "Replaces" Header", RFC 3891, September 2004.
1577 [14] Holtman, K., Mutz, A. and T. Hardie, "Media Feature Tag
1578 Registration Procedure", BCP 31, RFC 2506, March 1999.
1580 [15] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
1581 2246, January 1999.
1583 10.2 Informative References
1585 [16] Rosenberg, J., "A Presence Event Package for the Session
1586 Initiation Protocol (SIP)", RFC 3856, August 2004.
1588 [17] Rosenberg, J., "A Watcher Information Event Template-Package
1589 for the Session Initiation Protocol (SIP)", RFC 3857, August
1590 2004.
1592 [18] Mahy, R., "A Message Summary and Message Waiting Indication
1593 Event Package for the Session Initiation Protocol (SIP)", RFC
1594 3842, August 2004.
1596 [19] Rosenberg, J., Peterson, J., Schulzrinne, H. and G. Camarillo,
1597 "Best Current Practices for Third Party Call Control (3pcc) in
1598 the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April
1599 2004.
1601 [20] Rosenberg, J., "Obtaining and Using Globally Routable User
1602 Agent (UA) URIs (GRUU) in the Session Initiation Protocol
1603 (SIP)", draft-ietf-sip-gruu-02 (work in progress), July 2004.
1605 [21] Sparks, R. and A. Johnston, "Session Initiation Protocol Call
1606 Control - Transfer", draft-ietf-sipping-cc-transfer-03 (work in
1607 progress), October 2004.
1609 Authors' Addresses
1611 Jonathan Rosenberg
1612 Cisco Systems
1613 600 Lanidex Plaza
1614 Parsippany, NJ 07054
1615 US
1617 Phone: +1 973 952-5000
1618 EMail: jdrosen@cisco.com
1619 URI: http://www.jdrosen.net
1620 Henning Schulzrinne
1621 Columbia University
1622 M/S 0401
1623 1214 Amsterdam Ave.
1624 New York, NY 10027
1625 US
1627 EMail: schulzrinne@cs.columbia.edu
1628 URI: http://www.cs.columbia.edu/~hgs
1630 Rohan Mahy (editor)
1631 Airespace
1632 110 Nortech Parkway
1633 San Jose, CA 95134
1634 USA
1636 EMail: rohan@ekabal.com
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