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--------------------------------------------------------------------------------
2 Internet Engineering Task Force SIPPING WG
3 Internet Draft J. Rosenberg
4 dynamicsoft
5 H. Schulzrinne
6 Columbia U.
7 draft-ietf-sipping-dialog-package-00.txt
8 June 24, 2002
9 Expires: December 2002
11 A Session Initiation Protocol (SIP) Event Package for Dialog State
13 STATUS OF THIS MEMO
15 This document is an Internet-Draft and is in full conformance with
16 all provisions of Section 10 of RFC2026.
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 To view the list Internet-Draft Shadow Directories, see
32 http://www.ietf.org/shadow.html.
34 Abstract
36 This document defines a dialog event package for the SIP Events
37 architecture, along with a data format used in notifications for this
38 package. The dialog package allows users to subscribe to another
39 user, an receive notifications about the changes in state of INVITE
40 initiated dialogs that the user is involved in.
42 Table of Contents
44 1 Introduction ........................................ 4
45 2 Dialog Event Package ................................ 5
46 2.1 Event Package Name .................................. 5
47 2.2 Event Package Parameters ............................ 5
48 2.3 SUBSCRIBE Bodies .................................... 5
49 2.4 Subscription Duration ............................... 5
50 2.5 NOTIFY Bodies ....................................... 6
51 2.6 Notifier Processing of SUBSCRIBE Requests ........... 6
52 2.7 Notifier Generation of NOTIFY Requests .............. 7
53 2.7.1 The Dialog State Machine ............................ 7
54 2.7.2 Applying the state machine .......................... 9
55 2.8 Subscriber Processing of NOTIFY Requests ............ 10
56 2.9 Handling of Forked Requests ......................... 11
57 2.10 Rate of Notifications ............................... 11
58 2.11 State Agents ........................................ 11
59 3 Dialog Information Format ........................... 11
60 3.1 Structure of Dialog Information ..................... 12
61 3.1.1 Dialog Element ...................................... 12
62 3.1.2 State ............................................... 13
63 3.1.3 Local URI ........................................... 13
64 3.1.4 Remote URI .......................................... 13
65 3.1.5 Local Session Description ........................... 13
66 3.1.6 Remote Session Description .......................... 13
67 3.1.7 Remote Target ....................................... 13
68 3.1.8 Local CSeq .......................................... 14
69 3.1.9 Remote CSeq ......................................... 14
70 3.1.10 Duration ............................................ 14
71 3.2 Constructing Coherent State ......................... 14
72 3.3 Schema .............................................. 15
73 3.4 Example ............................................. 18
74 4 Security Considerations ............................. 20
75 5 IANA Considerations ................................. 20
76 5.1 application/dialog-info+xml MIME Registration ....... 20
77 5.2 URN Sub-Namespace Registration for
78 urn:ietf:params:xml:ns:dialog-info ............................. 21
79 6 Acknowledgements .................................... 22
80 7 Authors Addresses ................................... 22
81 8 Normative References ................................ 22
82 9 Informative References .............................. 23
84 1 Introduction
86 The SIP Events framework [1] defines general mechanisms for
87 subscription to, and notification of, events within SIP networks. It
88 introduces the notion of a package, which is a specific
89 "instantiation" of the events mechanism for a well-defined set of
90 events. Packages have been defined for user presence [8], watcher
91 information [9], and message waiting indicators [10], amongst others.
92 Here, we define an event package for INVITE initiated dialogs.
93 Dialogs refer to the SIP relationship established between two SIP
94 peers [2].
96 There are a variety of applications enabled through the knowledge of
97 dialog state. Some examples include:
99 Automatic Callback: In this basic PSTN application, user A calls
100 user B. User B is busy. User A would like to get a callback
101 when user B hangs up. When B hangs up, user A's phone
102 rings. When A picks it up, they here ringing, and are being
103 connected to B. In VoIP, this requires A to receive a
104 notification when the dialogs at A are complete.
106 Presence-Enabled Conferencing: In this application, a user A
107 wishes to set up a conference call with users B and C.
108 Rather than scheduling it, it is to be created
109 automatically when A, B and C are all available. To do
110 this, the server providing the application would like to
111 know whether A, B and C are "online", not idle, and not in
112 a phone call. Determining whether or not A, B and C are in
113 calls can be done in two ways. In the first, the server
114 acts as a call stateful proxy for users A, B and C, and
115 therefore knows their call state. This won't always be
116 possible, however, and it introduces scalability,
117 reliability, and operational complexities. Rather, the
118 server would subscriber to the dialog state of those users,
119 and receive notifications as it changes. This enables the
120 application to be provided in a distributed way; the server
121 need not reside in the same domain as the users.
123 IM Conference Alerts: In this application, a user can get an IM
124 sent to their phone whenever someone joins a conference
125 that the phone is involved in. The IM alerts are generated
126 by an application separate from the conference server.
128 In general, the dialog package allows for construction of distributed
129 applications, where the application requires information on dialog
130 state, but is not co-resident with the end user on which that state
131 resides.
133 2 Dialog Event Package
135 This section provides the details for defining a SIP Events package,
136 as specified by [1].
138 2.1 Event Package Name
140 The name of this event package is "dialog". This package name is
141 carried in the Event and Allow-Events header, as defined in [1].
143 2.2 Event Package Parameters
145 This package does not define any event package parameters.
147 2.3 SUBSCRIBE Bodies
149 A SUBSCRIBE for a dialog package MAY contain a body. This body
150 defines a filter to apply to the subscription.
152 A SUBSCRIBE for a dialog package MAY be sent without a body. This
153 implies the default subscription filtering policy. The default policy
154 is:
156 o Notifications are generated every time there is any change in
157 the state of any dialogs for the user identified in the
158 request URI of the SUBSCRIBE.
160 o Notifications do not normally contain full state; rather, they
161 only indicate the state of the dialog whose state has changed.
162 The exception is a NOTIFY sent in response to a SUBSCRIBE.
163 These NOTIFYs contain the complete view of dialog state.
165 o The notifications contain the identities of the participants
166 in the dialog, and the dialog identifiers. Additional
167 information, such as the route set, remote target URI, CSeq
168 numbers, SDP information, and so on, are not included normally
169 unless explicitly requested and/or explicitly authorized.
171 OPEN ISSUE: It might be useful to define a filter within
172 this document that would allow a subscriber to ask about a
173 specific dialog.
175 2.4 Subscription Duration
177 Dialog state changes fairly quickly; once established, a typical
178 phone call lasts a few minutes (this is different for other session
179 types, of course). However, the interval between new calls is
180 typically infrequent. As such, we arbitrarily choose a default
181 duration of one hour, and RECOMMEND that clients specify an explicit
182 duration.
184 There are two distinct use cases for dialog state. The first is when
185 a subscriber is interested in the state of a specific dialog (and
186 they are authorized to find out about just the state of that dialog).
187 In that case, when the dialog terminates, so too does the
188 subscription. In these cases, the value of the subscription duration
189 is largely irrelevant, and SHOULD be longer than the typical duration
190 of a dialog, about two hours would cover most dialogs.
192 In another case, a subscriber is interested in the state of all call
193 legs for a specific user. In these cases, a shorter interval makes
194 more sense. The default is one hour for these subscriptions.
196 2.5 NOTIFY Bodies
198 The body of the notification contains a dialog information document.
199 The format of this document is described in Section 3. Its MIME type
200 is "application/dialog-info+xml". All subscribers MUST support this
201 format, and MUST list its type in any Accept header in the SUBSCRIBE.
202 When no Accept header is present in the SUBSCRIBE, its default value
203 is "application/dialog-info+xml".
205 Other dialog information formats might be defined in the future. In
206 that case, the subscriptions MAY indicate support for other formats.
207 However, they MUST always support and list "application/dialog-
208 info+xml" as an allowed format.
210 Of course, the notifications generated by the server MUST be in one
211 of the formats specified in the Accept header in the SUBSCRIBE
212 request.
214 2.6 Notifier Processing of SUBSCRIBE Requests
216 The dialog information for a user contains very sensitive
217 information. Therefore, all subscriptions SHOULD be authenticated and
218 then authorized before approval. Authorization policy is at the
219 discretion of the administrator, as always. However, a few
220 recommendations can be made.
222 It is RECOMMENDED that if the policy of a user is that A is allowed
223 to call them, dialog subscriptions from user A be allowed. However,
224 the information provided in the notifications does not contain any
225 dialog identification information; merely an indication of whether
226 the user is in one or more calls, or not. Specifically, they should
227 not be able to find out any more information than if they sent an
228 INVITE.
230 It is RECOMMENDED that if a user agent registers with the address-
231 of-record X, that this user agent authorize subscriptions that come
232 from any entity that can authenticate itself as X. Complete
233 information on the dialog state SHOULD be sent in this case. This
234 authorization behavior allows a group of devices representing a
235 single user to all become aware of each other's state. This is useful
236 for applications such as single-line-extension.
238 2.7 Notifier Generation of NOTIFY Requests
240 Notifications are generated for the dialog package when a new dialog
241 comes into existence at a UA, or when the state or characteristics of
242 an existing dialog changes. Therefore, a model of dialog state is
243 needed in order to determine precisely when to send notifications,
244 and what their content should be. The SIP specification has a
245 reasonably well defined lifecycle for dialogs. However, it is not
246 explicitly modelled. This specification provides an explicit model of
247 dialog state through a finite state machine.
249 It is RECOMMENDED that NOTIFY requests only contain information on
250 the dialogs whose state has changed. However, if a notifier receives
251 a SUBSCRIBE request, the triggered NOTIFY SHOULD contain the state of
252 all dialogs that the subscriber is authorized to see.
254 2.7.1 The Dialog State Machine
256 Modelling of dialog state is complicated by two factors. The first is
257 forking, which can cause a single INVITE to generate many dialogs at
258 a UAC. The second is the differing views of state at the UAC and UAS.
259 We have chosen to handle the first issue by extending the dialog FSM
260 to include the states between transmission of the INVITE and the
261 creation of actual dialogs through receipt of 1xx and 2xx responses.
262 We have also chosen to use a single FSM for both UAC and UAS.
264 The FSM for dialog state is shown in Figure 1. The FSM is best
265 understood by considering the UAC and UAS cases separately.
267 The FSM is created in the "trying" state when the UAC sends an INVITE
268 request. Upon receipt of a 1xx without a tag (the "1xx-notag" event),
269 the FSM transitions to the "proceeding" state. Note that there is no
270 actual dialog yet, as defined by the SIP specification. However,
271 there is a "half-dialog", in the sense that two of the three
272 components of the dialog ID are known (the call identifier and local
273 tag). If a 1xx with a tag is received, the FSM transitions to the
274 early state. The full dialog identifier is now defined. Had a 2xx
275 +----------+ +----------+
276 | | 1xx-notag | |
277 | |----------->| |
278 | Trying | |Proceeding|-----+
279 | |---+ +-----| | |
280 | | | | | | |
281 +----------+ | | +----------+ |
282 | | | | | |
283 | | | | | |
284 +<--C-----C--+ |1xx-tag |
285 | | | | |
286 cancelled| | | V |
287 rejected| | |1xx-tag +----------+ |
288 | | +------->| | |2xx
289 | | | | |
290 +<--C--------------| Early | |
291 | | | | |
292 | | | | |
293 | | +----------+ |
294 | | 2xx | |
295 | +----------------+ | |
296 | | |2xx |
297 | | | |
298 V V V |
299 +----------+ +----------+ |
300 | | | | |
301 | | | | |
302 |Terminated|<-----------| Confirmed|<----+
303 | | hungup | |
304 | | error | |
305 +----------+ timeout +----------+
307 Figure 1: Dialog finite state machine
309 been received, the FSM would have transitioned to the "confirmed"
310 state.
312 If, after transitioning to the "early" or "confirmed" states, the UAC
313 receives another 1xx or 2xx with a different tag, another instance of
314 the FSM is created, initialized into the "early" or "confirmed" state
315 depending on the response code. The benefit of this approach is that
316 there will be a single FSM representing the entire state of the
317 invitation and resulting dialog when dealing with the common case of
318 no forking.
320 If the UAC should send a CANCEL, and then subsequently receive a 487
321 to its INVITE transaction, all FSMs spawned from that INVITE
322 transition to the "terminated" state with the event "canceled". If
323 the INVITE transaction terminates with a non-2xx response for any
324 other reason, all FSMs spawned from that INVITE transition to the
325 terminated state with the event "rejected".
327 Once in the confirmed state, the call is active. It can transition to
328 the terminated state if the UAC sends a BYE or receives a BYE
329 (corresponding to the "hungup" event), if a mid-dialog request
330 generates a 481 or 408 response (corresponding to the "error" event),
331 or a mid-dialog request generates no response (corresponding to the
332 "timeout" event).
334 From the perspective of the UAS, when an INVITE is received, the FSM
335 is created in the "trying" state. If it sends a 1xx without a tag,
336 the FSM transitions to the "proceeding" state. If a 1xx is sent with
337 a tag, the FSM transitions to the "early" state, and if a 2xx is
338 sent, it transitions to the "confirmed" state. If the UAS should
339 receive a CANCEL request and then generate a 487 response to the
340 INVITE (which can occur in the proceeding and early states), the FSM
341 transitions to the terminated state with the event "cancelled". If
342 the UAS should generate any other non-2xx final response to the
343 INVITE request, the FSM transitions to the terminated state with the
344 event "rejected". Once in the "confirmed" state, the transitions to
345 the "terminated" state occur for the same reasons they do in the case
346 of UAC.
348 There should never be a transition from the "trying" state
349 to the "terminated" state with the event "cancelled", since
350 the SIP specification prohibits transmission of CANCEL
351 until a provisional response is received. However, this
352 transition is defined in the FSM just to unify the
353 transitions from trying, proceeding, and early to the
354 terminated state.
356 2.7.2 Applying the state machine
358 The notifier MAY generate a NOTIFY request on any event transition of
359 the FSM. Whether it does or not is policy dependent. However, some
360 general guidelines are provided.
362 When the subscriber is unauthenticated, or is authenticated, but
363 represents a third party with no specific authorization policies, it
364 is RECOMMENDED that actual dialog states across all dialogs not be
365 reported. Rather, a single "virtual" dialog FSM be used, and event
366 transitions on that FSM be reported. If there is any dialog at the UA
367 whose state is "confirmed", the virtual FSM is in the "confirmed"
368 state. If there are no dialogs at the UA in the confirmed state, but
369 there is at least one in the "early" state, the virtual FSM is in the
370 "early" state. If there are no dialogs in the confirmed or early
371 states, but there is at least one in the "proceeding" state, the
372 virtual FSM is in the "proceeding" state. If there are no dialogs in
373 the confirmed, early, or proceeding states, but there is at least one
374 in the "trying" state, the virtual FSM is in the "trying" state.
375 Furthermore, it is RECOMMENDED that the notifications of changes in
376 the virtual FSM machine not convey any information except the state
377 of the FSM and its event transitions - no dialog identifiers (which
378 are ill-defined in this model in any case). The use of this virtual
379 FSM allows for minimal information to be conveyed. A subscriber
380 cannot know how many calls are in progress, or with whom, just that
381 there exists a call.
383 When the subscriber is authenticated, and has authenticated itself
384 with the same address-of-record that the UA itself uses, if no
385 explicit authorization policy is defined, it is RECOMMENDED that all
386 state transitions on all dialogs be reported, along with complete
387 dialog IDs.
389 The notifier MAY generate a NOTIFY request on any change in the
390 characteristics associated with the dialog. Since these include CSeq
391 numbers and SDP, receipt of re-INVITEs and UPDATE requests [11] which
392 modify this information MAY trigger notifications.
394 2.8 Subscriber Processing of NOTIFY Requests
396 The SIP Events framework expects packages to specify how a subscriber
397 processes NOTIFY requests in any package specific ways, and in
398 particular, how it uses the NOTIFY requests to contruct a coherent
399 view of the state of the subscribed resource.
401 Typically, the NOTIFY for the dialog package will only contain
402 information about those dialogs whose state has changed. To construct
403 a coherent view of the total state of all dialogs, a subscriber to
404 the dialog package will need to combine NOTIFYs received over time.
406 Notifications within this package can convey partial information;
407 that is, they can indicate information about a subset of the state
408 associated with the subscription. This means that an explicit
409 algorithm needs to be defined in order to construct coherent and
410 consistent state. The details of this mechanism are specific to the
411 particular document type. See Section 3.2 for information on
412 constructing coherent information from an application/dialog-info+xml
413 document.
415 2.9 Handling of Forked Requests
417 Since dialog state is distributed across the UA for a particular
418 user, it is reasonable and useful for a SUBSCRIBE request for dialog
419 state to fork, and reach multiple UA.
421 As a result, a forked SUBSCRIBE request for dialog state can install
422 multiple subscriptions. Subscribers to this package MUST be prepared
423 to install subscription state for each NOTIFY generated as a result
424 of a single SUBSCRIBE.
426 2.10 Rate of Notifications
428 For reasons of congestion control, it is important that the rate of
429 notifications not become excessive. As a result, it is RECOMMENDED
430 that the server not generate notifications for a single subscriber at
431 a rate faster than once every 5 seconds.
433 2.11 State Agents
435 Dialog state is ideally maintained in the user agents in which the
436 dialog resides. Therefore, the elements that maintain the dialog are
437 the ones best suited to handle subscriptions to it. Therefore, the
438 usage of state agents is NOT RECOMMENDED for this package.
440 3 Dialog Information Format
442 Dialog information is an XML document [3] that MUST be well-formed
443 and SHOULD be valid. Dialog information documents MUST be based on
444 XML 1.0 and MUST be encoded using UTF-8. This specification makes use
445 of XML namespaces for identifying dialog information documents and
446 document fragments. The namespace URI for elements defined by this
447 specification is a URN [4], using the namespace identifier 'ietf'
448 defined by [5] and extended by [6]. This URN is:
450 urn:ietf:params:xml:ns:dialog-info
451 A dialog information document begins with the root element tag
452 "dialog-info".
454 3.1 Structure of Dialog Information
456 A dialog information document starts with a dialog-info element. This
457 element has three mandatory attributes:
459 version: This attribute allows the recipient of dialog
460 information documents to properly order them. Versions
461 start at 0, and increment by one for each new document sent
462 to a subscriber. Versions are scoped within a subscription.
463 Versions MUST be representable using a 32 bit integer.
465 state: This attribute indicates whether the document contains
466 the full dialog information, or whether it contains only
467 information on those dialogs which have changed since the
468 previous document (partial).
470 entity: This attribute contains a URI that identifies the user
471 whose dialog information is reported in the remainder of
472 the document.
474 The dialog-info element has a series of dialog sub-elements. Each of
475 those represents a specific dialog.
477 3.1.1 Dialog Element
479 The dialog element reports information on a specific dialog. It has a
480 single mandatory attribute, id. The id attribute provides a single
481 string that can be used as an identifier for this dialog. This is a
482 different identifier than the formal dialog ID defined in SIP [2].
483 This identifier exists before the dialog exists, and remains
484 unchanged when the actual dialog is established.
486 There are a number of optional attributes which provide
487 identification information about the dialog:
489 call-id: This attribute is a string which represents the call-id
490 component of the dialog identifier.
492 local-tag: This attribute is a string which represents the
493 local-tag component of the dialog identifier.
495 remote-tag: This attribute is a string which represents the
496 remote-tag component of the dialog identifier. The remote
497 tag attribute won't be present if there is only a "half-
498 dialog", resulting from generation of a request that can
499 create a dialog.
501 direction: This attribute is either initiator or recipient, and
502 indicates whether the notifier was the initiator of the
503 dialog, or the recipient of the INVITE that created it.
505 The sub-elements of the dialog element provide additional information
506 about the dialog. The only mandatory one is status.
508 3.1.2 State
510 The state element indicates the state of the dialog. Its value is an
511 enumerated type describing one of the states in the FSM above. It has
512 an optional event attribute that can be used to indicate the event
513 which caused the transition into the current state, and an optional
514 code attribute that indicates the response code associated with the
515 transition, assuming the event was 1xx-tag, 1xx-notag, or 2xx.
517 3.1.3 Local URI
519 The local-uri element indicates the local URI, as defined in [2]. It
520 has an optional attribute, display-name, that contains the display
521 name from the local URI.
523 3.1.4 Remote URI
525 The remote-uri element indicates the remote URI, as defined in [2].
526 It has an optional attribute, display-name, that contains the display
527 name from the remote URI.
529 3.1.5 Local Session Description
531 The local-session-description element contains the session
532 description used by the notifier for its end of the dialog. This
533 element should generally NOT be included in the notifications, unless
534 explicitly requested by the subscriber. It has a single attribute,
535 type, which indicates the MIME media type of the session description.
537 3.1.6 Remote Session Description
539 The remote-session-description element contains the session
540 description used by the peer of the notifier for its end of the
541 dialog. This element should generally NOT be included in the
542 notifications, unless explicitly requested by the subscriber. It has
543 a single attribute, type, which indicates the MIME media type of the
544 session description.
546 3.1.7 Remote Target
547 The remote-target contains the remote-target URI as constructed by
548 the user agent for this dialog, as defined in RFC BBBB [2]. This
549 element should generally not be included in notifications, unless
550 explicitly requested by the subscriber.
552 3.1.8 Local CSeq
554 The local-cseq element contains the most recent value of the CSeq
555 header used by the UA in an outgoing request on the dialog. This
556 element should generally NOT be included in the notifications, unless
557 explicitly requested by the subscriber. If no CSeq has yet been
558 defined, the value of the element is -1.
560 3.1.9 Remote CSeq
562 The remote-cseq element contains the most recent value of the CSeq
563 header seen by the UA in an incoming request on the dialog. This
564 element should generally NOT be included in the notifications, unless
565 explicitly requested by the subscriber. If no CSeq has yet been
566 defined, the value of the element is -1.
568 3.1.10 Duration
570 The duration element contains the amount of time, in seconds, since
571 the FSM was created.
573 3.2 Constructing Coherent State
575 The dialog information subscriber maintains a table for the list of
576 dialogs. The table contains a row for each dialog. Each row is
577 indexed by an ID, present in the "id" attribute of the "dialog"
578 element. The contents of each row contain the state of that dialog as
579 conveyed in the document. The table is also associated with a version
580 number. The version number MUST be initialized with the value of the
581 "version" attribute from the "dialog-info" element in the first
582 document received. Each time a new document is received, the value of
583 the local version number, and the "version" attribute in the new
584 document, are compared. If the value in the new document is one
585 higher than the local version number, the local version number is
586 increased by one, and the document is processed. If the value in the
587 document is more than one higher than the local version number, the
588 local version number is set to the value in the new document, the
589 document is processed, and the subscriber SHOULD generate a refresh
590 request to trigger a full state notification. If the value in the
591 document is less than the local version, the document is discarded
592 without processing.
594 The processing of the dialog information document depends on whether
595 it contains full or partial state. If it contains full state,
596 indicated by the value of the "state" attribute in the "dialog-info"
597 element, the contents of the table are flushed. They are repopulated
598 from the document. A new row in the table is created for each
599 "dialog" element. If the document contains partial state, as
600 indicated by the value of the "state" attribute in the "dialog-info"
601 element, the document is used to update the table. For each "dialog"
602 element in the document, the subscriber checks to see whether a row
603 exists for that dialog. This check is done by comparing the ID in the
604 "id" attribute of the "dialog" element with the ID associated with
605 the row. If the dialog doesn't exist in the table, a row is added,
606 and its state is set to the information from that "dialog" element.
607 If the dialog does exist, its state is updated to be the information
608 from that "dialog" element. If a row is updated or created, such that
609 its state is now terminated, that entry MAY be removed from the table
610 at any time.
612 3.3 Schema
614 The following is the schema for the application/dialog-info+xml type:
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740 3.4 Example
742 For example, if a UAC sends an INVITE that looks like, in part:
744 INVITE sip:callee@foo.com SIP/2.0
745 From: sip:caller@bar.com;tag=123
746 To: sip:callee@foo.com
747 Call-ID: 987@1.2.3.4
749 The XML document in a notification might look like:
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762 If a 1xx with a tag is received, the XML document in a notification
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777 If it receives a second 1xx, with a different tag, this results in
778 the creation of a second dialog:
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795 If a 200 OK is received on the second dialog, it moves to confirmed:
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808 32 seconds later, the other early dialog terminates because no 2xx is
809 received for it. This implies that it was successfully cancelled, and
810 therefore the following notification is sent:
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823 4 Security Considerations
825 Subscriptions to dialog state can reveal very sensitive information.
826 For this reason, this specification recommends authentication and
827 authorization of subscriptions, and provides guidelines on sensible
828 authorization policies.
830 Since the data in notifications is sensitive as well, end-to-end SIP
831 encryption mechanisms using S/MIME MAY be used to protect it.
833 5 IANA Considerations
835 This document registers a new MIME type, application/dialog-info+xml
836 and registers a new XML namespace.
838 5.1 application/dialog-info+xml MIME Registration
840 MIME media type name: application
842 MIME subtype name: dialog-info+xml
844 Mandatory parameters: none
846 Optional parameters: Same as charset parameter application/xml
847 as specified in RFC 3023 [7].
849 Encoding considerations: Same as encoding considerations of
850 application/xml as specified in RFC 3023 [7].
852 Security considerations: See Section 10 of RFC 3023 [7] and
853 Section 4 of this specification.
855 Interoperability considerations: none.
857 Published specification: This document.
859 Applications which use this media type: This document type has
860 been used to support SIP applications such as call return
861 and auto-conference.
863 Additional Information:
865 Magic Number: None
867 File Extension: .dif or .xml
869 Macintosh file type code: "TEXT"
871 Personal and email address for further information: Jonathan
872 Rosenberg,
874 Intended usage: COMMON
876 Author/Change controller: The IETF.
878 5.2 URN Sub-Namespace Registration for urn:ietf:params:xml:ns:dialog-
879 info
881 This section registers a new XML namespace, as per the guidelines in
882 [6].
884 URI: The URI for this namespace is
885 urn:ietf:params:xml:ns:dialog-info.
887 Registrant Contact: IETF, SIMPLE working group,
888 , Jonathan Rosenberg
889 .
891 XML:
893 BEGIN
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901 Dialog Information Namespace
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904 Namespace for Dialog Information
905 application/dialog-info+xml
906 See RFCXXXX.
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