Internet Engineering Task Force SIPPING WG Internet Draft J. Rosenberg dynamicsoft H. Schulzrinne Columbia U. draft-ietf-sipping-dialog-package-01.txt March 1, 2003 Expires: September 1, 2003 An INVITE Inititiated Dialog Event Package for the Session Initiation Protocol (SIP) STATUS OF THIS MEMO This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt To view the list Internet-Draft Shadow Directories, see http://www.ietf.org/shadow.html. Abstract This document defines a dialog event package for the SIP Events architecture, along with a data format used in notifications for this package. The dialog package allows users to subscribe to another user, an receive notifications about the changes in state of INVITE initiated dialogs that the user is involved in. J. Rosenberg et. al. [Page 1] Internet Draft Dialog Package March 1, 2003 Table of Contents 1 Introduction ........................................ 3 2 Dialog Event Package ................................ 4 2.1 Event Package Name .................................. 4 2.2 Event Package Parameters ............................ 4 2.3 SUBSCRIBE Bodies .................................... 4 2.4 Subscription Duration ............................... 5 2.5 NOTIFY Bodies ....................................... 6 2.6 Notifier Processing of SUBSCRIBE Requests ........... 6 2.7 Notifier Generation of NOTIFY Requests .............. 6 2.7.1 The Dialog State Machine ............................ 7 2.7.2 Applying the state machine .......................... 8 2.8 Subscriber Processing of NOTIFY Requests ............ 10 2.9 Handling of Forked Requests ......................... 11 2.10 Rate of Notifications ............................... 11 2.11 State Agents ........................................ 11 3 Dialog Information Format ........................... 11 3.1 Structure of Dialog Information ..................... 12 3.1.1 Dialog Element ...................................... 12 3.1.2 State ............................................... 13 3.1.3 Local URI ........................................... 13 3.1.4 Remote URI .......................................... 13 3.1.5 Local Session Description ........................... 13 3.1.6 Remote Session Description .......................... 14 3.1.7 Remote Target ....................................... 14 3.1.8 Local CSeq .......................................... 14 3.1.9 Remote CSeq ......................................... 14 3.1.10 Duration ............................................ 14 3.2 Constructing Coherent State ......................... 14 3.3 Schema .............................................. 15 3.4 Example ............................................. 18 4 Security Considerations ............................. 21 5 IANA Considerations ................................. 21 5.1 application/dialog-info+xml MIME Registration ....... 21 5.2 URN Sub-Namespace Registration for urn:ietf:params:xml:ns:dialog-info ............................. 22 6 Acknowledgements .................................... 23 7 Authors Addresses ................................... 23 8 Normative References ................................ 23 9 Informative References .............................. 24 J. Rosenberg et. al. [Page 2] Internet Draft Dialog Package March 1, 2003 1 Introduction The SIP Events framework [1] defines general mechanisms for subscription to, and notification of, events within SIP networks. It introduces the notion of a package, which is a specific "instantiation" of the events mechanism for a well-defined set of events. Packages have been defined for user presence [9], watcher information [10], and message waiting indicators [11], amongst others. Here, we define an event package for INVITE initiated dialogs. Dialogs refer to the SIP relationship established between two SIP peers [2]. Dialogs can be created by many methods, although RFC 3261 defines only one - the INVITE method. RFC 3265 defines the SUBSCRIBE and NOTIFY methods, which also create dialogs. However, the usage of this package to model transitions in the state of those dialogs is out of the scope of this specification. There are a variety of applications enabled through the knowledge of INVITE dialog state. Some examples include: Automatic Callback: In this basic Public Switched Telephone Network (PSTN) application, user A calls user B. User B is busy. User A would like to get a callback when user B hangs up. When B hangs up, user A's phone rings. When A picks it up, they here ringing, and are being connected to B. To implement this with SIP, a mechanism is required for B to receive a notification when the dialogs at A are complete. Presence-Enabled Conferencing: In this application, a user A wishes to set up a conference call with users B and C. Rather than scheduling it, it is to be created automatically when A, B and C are all available. To do this, the server providing the application would like to know whether A, B and C are "online", not idle, and not in a phone call. Determining whether or not A, B and C are in calls can be done in two ways. In the first, the server acts as a call stateful proxy for users A, B and C, and therefore knows their call state. This won't always be possible, however, and it introduces scalability, reliability, and operational complexities. Rather, the server would subscriber to the dialog state of those users, and receive notifications as it changes. This enables the application to be provided in a distributed way; the server need not reside in the same domain as the users. IM Conference Alerts: In this application, a user can get an IM sent to their phone whenever someone joins a conference that the phone is involved in. The IM alerts are generated by an application separate from the conference server. J. Rosenberg et. al. [Page 3] Internet Draft Dialog Package March 1, 2003 In general, the dialog package allows for construction of distributed applications, where the application requires information on dialog state, but is not co-resident with the end user on which that state resides. 2 Dialog Event Package This section provides the details for defining a SIP Events package, as specified by [1]. 2.1 Event Package Name The name of this event package is "dialog". This package name is carried in the Event and Allow-Events header, as defined in [1]. 2.2 Event Package Parameters This package defines three Event Package parameters. They are call- id, to-tag and from-tag. If a subscription to a specific dialog is requested, all three of these parameters MUST be present. They identify the dialog or that is being subscribed to. The to-tag is matched against the local tag, the from-tag is matched against the remote tag, and the call-id is matched against the Call-ID. It is also possible to subscribe to the set of dialogs created as a result of a single INVITE sent by a UAC. In that case, the call-id and to-tag MUST be present. The to-tag is matched against the local tag, and the call-id is matched against the Call-ID. The BNF for these parameters is: call-id = "call-id" EQUAL SWS DQUOTE callid DQUOTE ;;callid, EQUAL, SWS, DQUOTE from rfc3261 from-tag = "from-tag" EQUAL token to-tag = "to-tag" EQUAL token Note that the call-id parameter is a quoted string. This is because the BNF for word (which is used by callid) allows for characters not allowed within token. 2.3 SUBSCRIBE Bodies A SUBSCRIBE for a dialog package MAY contain a body. This body defines a filter to apply to the subscription. Filter documents are not specified in this document, and at the time of writing, are J. Rosenberg et. al. [Page 4] Internet Draft Dialog Package March 1, 2003 expected to be the subject of future standardization activity. A SUBSCRIBE for a dialog package MAY be sent without a body. This implies the default subscription filtering policy. The default policy is: o If the Event header field contained dialog identifiers, notifications are generated every time there is a change in the state of any matching dialogs for the user identified in the request URI of the SUBSCRIBE. o If there were no dialog identifiers in the Event header field, notifications are generated every time there is any change in the state of any dialogs for the user identified in the request URI of the SUBSCRIBE. o Notifications do not normally contain full state; rather, they only indicate the state of the dialog whose state has changed. The exception is a NOTIFY sent in response to a SUBSCRIBE. These NOTIFYs contain the complete view of dialog state. o The notifications contain the identities of the participants in the dialog, and the dialog identifiers. Additional information, such as the route set, remote target URI, CSeq numbers, SDP information, and so on, are not included normally unless explicitly requested and/or explicitly authorized. 2.4 Subscription Duration Dialog state changes fairly quickly; once established, a typical phone call lasts a few minutes (this is different for other session types, of course). However, the interval between new calls is typically infrequent. As such, we arbitrarily choose a default duration of one hour, and RECOMMEND that clients specify an explicit duration. There are two distinct use cases for dialog state. The first is when a subscriber is interested in the state of a specific dialog or dialogs (and they are authorized to find out about just the state of those dialogs). In that case, when the dialogs terminate, so too does the subscription. In these cases, the value of the subscription duration is largely irrelevant, and SHOULD be longer than the typical duration of a dialog, about two hours would cover most dialogs. In another case, a subscriber is interested in the state of all dialogs for a specific user. In these cases, a shorter interval makes more sense. The default is one hour for these subscriptions. J. Rosenberg et. al. [Page 5] Internet Draft Dialog Package March 1, 2003 2.5 NOTIFY Bodies As described in RFC 3265 [1], the NOTIFY message will contain bodies that describe the state of the subscribed resource. This body is in a format listed in the Accept header field of the SUBSCRIBE, or a package-specific default if the Accept header field was omitted from the SUBSCRIBE. In this event package, the body of the notification contains a dialog information document. This document describes the state of one or more dialogs associated with the subscribed resource. All subscribers and notifiers MUST support the "application/dialog-info+xml" data format described in 3. The subscribe request MAY contain an Accept header field. If no such header field is present, it has a default value of "application/dialog-info+xml". If the header field is present, it MUST include "application/dialog-info+xml", and MAY include any other types capable of representing dialog state. Of course, the notifications generated by the server MUST be in one of the formats specified in the Accept header field in the SUBSCRIBE request. 2.6 Notifier Processing of SUBSCRIBE Requests The dialog information for a user contains sensitive information. Therefore, all subscriptions SHOULD be authenticated and then authorized before approval. All implementors of this package MUST support the digest authentication mechanism as a baseline. Authorization policy is at the discretion of the administrator, as always. However, a few recommendations can be made. It is RECOMMENDED that, if the policy of user B is that user A is allowed to call them, dialog subscriptions from user A be allowed. However, the information provided in the notifications does not contain any dialog identification information; merely an indication of whether the user is in one or more calls, or not. Specifically, they should not be able to find out any more information than if they sent an INVITE. It is RECOMMENDED that if a user agent registers with the address- of-record X, that this user agent authorize subscriptions that come from any entity that can authenticate itself as X. Complete information on the dialog state SHOULD be sent in this case. This authorization behavior allows a group of devices representing a single user to all become aware of each other's state. This is useful for applications such as single-line-extension. 2.7 Notifier Generation of NOTIFY Requests J. Rosenberg et. al. [Page 6] Internet Draft Dialog Package March 1, 2003 Notifications are generated for the dialog package when an INVITE request is sent, when a new dialog comes into existence at a UA, or when the state or characteristics of an existing dialog changes. Therefore, a model of dialog state is needed in order to determine precisely when to send notifications, and what their content should be. The SIP specification has a reasonably well defined lifecycle for dialogs. However, it is not explicitly modelled. This specification provides an explicit model of dialog state through a finite state machine. It is RECOMMENDED that NOTIFY requests only contain information on the dialogs whose state has changed. However, if a notifier receives a SUBSCRIBE request, the triggered NOTIFY SHOULD contain the state of all dialogs that the subscriber is authorized to see. 2.7.1 The Dialog State Machine Modelling of dialog state is complicated by two factors. The first is forking, which can cause a single INVITE to generate many dialogs at a UAC. The second is the differing views of state at the UAC and UAS. We have chosen to handle the first issue by extending the dialog FSM to include the states between transmission of the INVITE and the creation of actual dialogs through receipt of 1xx and 2xx responses. As a result, this specification supports the notion of dialog state for dialogs before they are fully instantiated. We have also chosen to use a single FSM for both UAC and UAS. The FSM for dialog state is shown in Figure 1. The FSM is best understood by considering the UAC and UAS cases separately. The FSM is created in the "trying" state when the UAC sends an INVITE request. Upon receipt of a 1xx without a tag (the "1xx-notag" event), the FSM transitions to the "proceeding" state. Note that there is no actual dialog yet, as defined by the SIP specification. However, there is a "half-dialog", in the sense that two of the three components of the dialog ID are known (the call identifier and local tag). If a 1xx with a tag is received, the FSM transitions to the early state. The full dialog identifier is now defined. Had a 2xx been received, the FSM would have transitioned to the "confirmed" state. If, after transitioning to the "early" or "confirmed" states, the UAC receives another 1xx or 2xx respectively with a different tag, another instance of the FSM is created, initialized into the "early" or "confirmed" state respectively. The benefit of this approach is that there will be a single FSM representing the entire state of the J. Rosenberg et. al. [Page 7] Internet Draft Dialog Package March 1, 2003 invitation and resulting dialog when dealing with the common case of no forking. If the UAC should send a CANCEL, and then subsequently receive a 487 to its INVITE transaction, all FSMs spawned from that INVITE transition to the "terminated" state with the event "cancelled". If the INVITE transaction terminates with a non-2xx response for any other reason, all FSMs spawned from that INVITE transition to the terminated state with the event "rejected". Once in the confirmed state, the call is active. It can transition to the terminated state if the UAC sends a BYE or receives a BYE (corresponding to the "hungup" event), if a mid-dialog request generates a 481 or 408 response (corresponding to the "error" event), or a mid-dialog request generates no response (corresponding to the "timeout" event). From the perspective of the UAS, when an INVITE is received, the FSM is created in the "trying" state. If it sends a 1xx without a tag, the FSM transitions to the "proceeding" state. If a 1xx is sent with a tag, the FSM transitions to the "early" state, and if a 2xx is sent, it transitions to the "confirmed" state. If the UAS should receive a CANCEL request and then generate a 487 response to the INVITE (which can occur in the proceeding and early states), the FSM transitions to the terminated state with the event "cancelled". If the UAS should generate any other non-2xx final response to the INVITE request, the FSM transitions to the terminated state with the event "rejected". Once in the "confirmed" state, the transitions to the "terminated" state occur for the same reasons they do in the case of UAC. There should never be a transition from the "trying" state to the "terminated" state with the event "cancelled", since the SIP specification prohibits transmission of CANCEL until a provisional response is received. However, this transition is defined in the FSM just to unify the transitions from trying, proceeding, and early to the terminated state. 2.7.2 Applying the state machine The notifier MAY generate a NOTIFY request on any event transition of the FSM. Whether it does or not is policy dependent. However, some general guidelines are provided. When the subscriber is unauthenticated, or is authenticated, but represents a third party with no specific authorization policies, it J. Rosenberg et. al. [Page 8] Internet Draft Dialog Package March 1, 2003 +----------+ +----------+ | | 1xx-notag | | | |----------->| | | Trying | |Proceeding|-----+ | |---+ +-----| | | | | | | | | | +----------+ | | +----------+ | | | | | | | | | | | | | +<--C-----C--+ |1xx-tag | | | | | | cancelled| | | V | rejected| | |1xx-tag +----------+ | | | +------->| | |2xx | | | | | +<--C--------------| Early |-----C----+1xx-tag | | | | | | w. new tag | | | |<----C----+ (new | | +----------+ | FSM | | 2xx | | instance | +----------------+ | | created) | | |2xx | | | | | V V V | +----------+ +----------+ | | | | | | | | | | | |Terminated|<-----------| Confirmed|<----+ | | hungup | | | | error | | +----------+ timeout +----------+ | ^ | | | | +------+ 2xx w. new tag (new FSM instance created) Figure 1: Dialog finite state machine J. Rosenberg et. al. [Page 9] Internet Draft Dialog Package March 1, 2003 dialogs (i.e., there are no dialog identifiers in the Event header field) are permitted. In that case, actual dialog states across all dialogs not be reported. Rather, a single "virtual" dialog FSM be used, and event transitions on that FSM be reported. If there is any dialog at the UA whose state is "confirmed", the virtual FSM is in the "confirmed" state. If there are no dialogs at the UA in the confirmed state, but there is at least one in the "early" state, the virtual FSM is in the "early" or "confirmed" state. If there are no dialogs in the confirmed or early states, but there is at least one in the "proceeding" state, the virtual FSM is in the "proceeding", "early" or "confirmed" state. If there are no dialogs in the confirmed, early, or proceeding states, but there is at least one in the "trying" state, the virtual FSM is in the "trying", "proceeding", "early" or "confirmed" state. The choice about which state to use depends on whether the UA wishes to let unknown users that their phone is ringing, as opposed to in an active call. It is RECOMMENDED that, in the absence of any preference, "confirmed" is used in all cases. Furthermore, it is RECOMMENDED that the notifications of changes in the virtual FSM machine not convey any information except the state of the FSM and its event transitions - no dialog identifiers (which are ill-defined in this model in any case). The use of this virtual FSM allows for minimal information to be conveyed. A subscriber cannot know how many calls are in progress, or with whom, just that there exists a call. This is the same information they would receive if they simply sent an INVITE to the user instead; a 486 response would indicate that they are on a call. When the subscriber is authenticated, and has authenticated itself with the same address-of-record that the UA itself uses, if no explicit authorization policy is defined, it is RECOMMENDED that all state transitions on dialogs that have been subscribed to (which is either all of them, if no dialog identifiers were present in the Event header field, or a specific set of them identified by the Event header field parameters) be reported, along with complete dialog IDs. The notifier MAY generate a NOTIFY request on any change in the characteristics associated with the dialog. Since these include CSeq numbers and SDP, receipt of re-INVITEs and UPDATE requests [3] which modify this information MAY trigger notifications. 2.8 Subscriber Processing of NOTIFY Requests The SIP Events framework expects packages to specify how a subscriber processes NOTIFY requests in any package specific ways, and in particular, how it uses the NOTIFY requests to contruct a coherent view of the state of the subscribed resource. Typically, the NOTIFY for the dialog package will only contain J. Rosenberg et. al. [Page 10] Internet Draft Dialog Package March 1, 2003 information about those dialogs whose state has changed. To construct a coherent view of the total state of all dialogs, a subscriber to the dialog package will need to combine NOTIFYs received over time. Notifications within this package can convey partial information; that is, they can indicate information about a subset of the state associated with the subscription. This means that an explicit algorithm needs to be defined in order to construct coherent and consistent state. The details of this mechanism are specific to the particular document type. See Section 3.2 for information on constructing coherent information from an application/dialog-info+xml document. 2.9 Handling of Forked Requests Since dialog state is distributed across the UA for a particular user, it is reasonable and useful for a SUBSCRIBE request for dialog state to fork, and reach multiple UA. As a result, a forked SUBSCRIBE request for dialog state can install multiple subscriptions. Subscribers to this package MUST be prepared to install subscription state for each NOTIFY generated as a result of a single SUBSCRIBE. 2.10 Rate of Notifications For reasons of congestion control, it is important that the rate of notifications not become excessive. As a result, it is RECOMMENDED that the server not generate notifications for a single subscriber at a rate faster than once every 5 seconds. 2.11 State Agents Dialog state is ideally maintained in the user agents in which the dialog resides. Therefore, the elements that maintain the dialog are the ones best suited to handle subscriptions to it. Therefore, the usage of state agents is NOT RECOMMENDED for this package. 3 Dialog Information Format Dialog information is an XML document [4] that MUST be well-formed and SHOULD be valid. Dialog information documents MUST be based on XML 1.0 and MUST be encoded using UTF-8. This specification makes use of XML namespaces for identifying dialog information documents and document fragments. The namespace URI for elements defined by this specification is a URN [5], using the namespace identifier 'ietf' defined by [6] and extended by [7]. This URN is: J. Rosenberg et. al. [Page 11] Internet Draft Dialog Package March 1, 2003 urn:ietf:params:xml:ns:dialog-info A dialog information document begins with the root element tag "dialog-info". 3.1 Structure of Dialog Information A dialog information document starts with a dialog-info element. This element has three mandatory attributes: version: This attribute allows the recipient of dialog information documents to properly order them. Versions start at 0, and increment by one for each new document sent to a subscriber. Versions are scoped within a subscription. Versions MUST be representable using a 32 bit integer. state: This attribute indicates whether the document contains the full dialog information, or whether it contains only information on those dialogs which have changed since the previous document (partial). entity: This attribute contains a URI that identifies the user whose dialog information is reported in the remainder of the document. The dialog-info element has a series of dialog sub-elements. Each of those represents a specific dialog. 3.1.1 Dialog Element The dialog element reports information on a specific dialog or "half-dialog". It has a single mandatory attribute, id. The id attribute provides a single string that can be used as an identifier for this dialog or "half-dialog". This is a different identifier than the dialog ID defined in RFC 3261 [2], but related to it. For a caller, the id is created when an INVITE request is sent. When a 1xx with a tag, or a 2xx is received, the dialog is formally created. The id remains unchanged. However, if an additional 1xx or 2xx is received, resulting in the creation of another dialog (and resulting FSM), that dialog is allocated a new id. For a callee, the id is created when an INVITE outside of an existing dialog is received. When a 2xx or a 1xx with a tag is sent, creating the dialog, the id remains unchanged. J. Rosenberg et. al. [Page 12] Internet Draft Dialog Package March 1, 2003 The id MUST be unique amongst all dialogs at a UA. There are a number of optional attributes which provide identification information about the dialog: call-id: This attribute is a string which represents the call-id component of the dialog identifier. local-tag: This attribute is a string which represents the local-tag component of the dialog identifier. remote-tag: This attribute is a string which represents the remote-tag component of the dialog identifier. The remote tag attribute won't be present if there is only a "half- dialog", resulting from the generation of an INVITE for which no final responses or provisional responses with tags has been received. direction: This attribute is either initiator or recipient, and indicates whether the notifier was the initiator of the dialog, or the recipient of the INVITE that created it. The sub-elements of the dialog element provide additional information about the dialog. The only mandatory one is state. 3.1.2 State The state element indicates the state of the dialog. Its value is an enumerated type describing one of the states in the FSM above. It has an optional event attribute that can be used to indicate the event which caused the transition into the current state, and an optional code attribute that indicates the response code associated with the transition, assuming the event was 1xx-tag, 1xx-notag, or 2xx. 3.1.3 Local URI The local-uri element indicates the local URI, as defined in [2]. It has an optional attribute, display-name, that contains the display name from the local URI. 3.1.4 Remote URI The remote-uri element indicates the remote URI, as defined in [2]. It has an optional attribute, display-name, that contains the display name from the remote URI. 3.1.5 Local Session Description J. Rosenberg et. al. [Page 13] Internet Draft Dialog Package March 1, 2003 The local-session-description element contains the session description used by the notifier for its end of the dialog. This element should generally NOT be included in the notifications, unless explicitly requested by the subscriber. It has a single attribute, type, which indicates the MIME media type of the session description. 3.1.6 Remote Session Description The remote-session-description element contains the session description used by the peer of the notifier for its end of the dialog. This element should generally NOT be included in the notifications, unless explicitly requested by the subscriber. It has a single attribute, type, which indicates the MIME media type of the session description. 3.1.7 Remote Target The remote-target contains the remote-target URI as constructed by the user agent for this dialog, as defined in RFC 3261 [2]. This element should generally not be included in notifications, unless explicitly requested by the subscriber. 3.1.8 Local CSeq The local-cseq element contains the most recent value of the CSeq header used by the UA in an outgoing request on the dialog. This element should generally NOT be included in the notifications, unless explicitly requested by the subscriber. If no CSeq has yet been defined, the value of the element is -1. 3.1.9 Remote CSeq The remote-cseq element contains the most recent value of the CSeq header seen by the UA in an incoming request on the dialog. This element should generally NOT be included in the notifications, unless explicitly requested by the subscriber. If no CSeq has yet been defined, the value of the element is -1. 3.1.10 Duration The duration element contains the amount of time, in seconds, since the FSM was created. 3.2 Constructing Coherent State The dialog information subscriber maintains a table for the list of dialogs. The table contains a row for each dialog. Each row is indexed by an ID, present in the "id" attribute of the "dialog" J. Rosenberg et. al. [Page 14] Internet Draft Dialog Package March 1, 2003 element. The contents of each row contain the state of that dialog as conveyed in the document. The table is also associated with a version number. The version number MUST be initialized with the value of the "version" attribute from the "dialog-info" element in the first document received. Each time a new document is received, the value of the local version number, and the "version" attribute in the new document, are compared. If the value in the new document is one higher than the local version number, the local version number is increased by one, and the document is processed. If the value in the document is more than one higher than the local version number, the local version number is set to the value in the new document, and the document is processed. If the document did not contain full state, the subscriber SHOULD generate a refresh request to trigger a full state notification. If the value in the document is less than the local version, the document is discarded without processing. The processing of the dialog information document depends on whether it contains full or partial state. If it contains full state, indicated by the value of the "state" attribute in the "dialog-info" element, the contents of the table are flushed. They are repopulated from the document. A new row in the table is created for each "dialog" element. If the document contains partial state, as indicated by the value of the "state" attribute in the "dialog-info" element, the document is used to update the table. For each "dialog" element in the document, the subscriber checks to see whether a row exists for that dialog. This check is done by comparing the ID in the "id" attribute of the "dialog" element with the ID associated with the row. If the dialog doesn't exist in the table, a row is added, and its state is set to the information from that "dialog" element. If the dialog does exist, its state is updated to be the information from that "dialog" element. If a row is updated or created, such that its state is now terminated, that entry MAY be removed from the table at any time. 3.3 Schema The following is the schema for the application/dialog-info+xml type: J. Rosenberg et. al. [Page 15] Internet Draft Dialog Package March 1, 2003 J. Rosenberg et. al. [Page 16] Internet Draft Dialog Package March 1, 2003 J. Rosenberg et. al. [Page 17] Internet Draft Dialog Package March 1, 2003 3.4 Example For example, if a UAC sends an INVITE that looks like, in part: INVITE sip:bob@example.com SIP/2.0 Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8 Max-Forwards: 70 To: Bob From: Alice ;tag=1928301774 Call-ID: a84b4c76e66710 CSeq: 314159 INVITE Contact: Content-Type: application/sdp Content-Length: 142 [SDP not shown] The XML document in a notification from Alice might look like: J. Rosenberg et. al. [Page 18] Internet Draft Dialog Package March 1, 2003 trying If the following 180 response is received: SIP/2.0 180 Ringing Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8 To: Bob ;tag=456887766 From: Alice ;tag=1928301774 Call-ID: a84b4c76e66710 CSeq: 314159 INVITE Contact: The XML document in a notification might look like: early If it receives a second 180 with a different tag: J. Rosenberg et. al. [Page 19] Internet Draft Dialog Package March 1, 2003 SIP/2.0 180 Ringing Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8 To: Bob ;tag=hh76a From: Alice ;tag=1928301774 Call-ID: a84b4c76e66710 CSeq: 314159 INVITE Contact: This results in the creation of a second dialog: early early If a 200 OK is received on the second dialog, it moves to confirmed: confirmed J. Rosenberg et. al. [Page 20] Internet Draft Dialog Package March 1, 2003 32 seconds later, the other early dialog terminates because no 2xx is received for it. This implies that it was successfully cancelled, and therefore the following notification is sent: terminated 4 Security Considerations Subscriptions to dialog state can reveal sensitive information. For this reason, Section 2.6 discusses authentication and authorization of subscriptions, and provides guidelines on sensible authorization policies. All implementations of this package MUST support the digest authentication mechanism. Since the data in notifications is sensitive as well, end-to-end SIP encryption mechanisms using S/MIME MAY be used to protect it. 5 IANA Considerations This document registers a new MIME type, application/dialog-info+xml and registers a new XML namespace. 5.1 application/dialog-info+xml MIME Registration MIME media type name: application MIME subtype name: dialog-info+xml Mandatory parameters: none Optional parameters: Same as charset parameter application/xml as specified in RFC 3023 [8]. Encoding considerations: Same as encoding considerations of J. Rosenberg et. al. [Page 21] Internet Draft Dialog Package March 1, 2003 application/xml as specified in RFC 3023 [8]. Security considerations: See Section 10 of RFC 3023 [8] and Section 4 of this specification. Interoperability considerations: none. Published specification: This document. Applications which use this media type: This document type has been used to support SIP applications such as call return and auto-conference. Additional Information: Magic Number: None File Extension: .dif or .xml Macintosh file type code: "TEXT" Personal and email address for further information: Jonathan Rosenberg, Intended usage: COMMON Author/Change controller: The IETF. 5.2 URN Sub-Namespace Registration for urn:ietf:params:xml:ns:dialog- info This section registers a new XML namespace, as per the guidelines in [7]. URI: The URI for this namespace is urn:ietf:params:xml:ns:dialog-info. Registrant Contact: IETF, SIMPLE working group, , Jonathan Rosenberg . XML: BEGIN J. Rosenberg et. al. [Page 22] Internet Draft Dialog Package March 1, 2003 Dialog Information Namespace

Namespace for Dialog Information

application/dialog-info+xml

See RFCXXXX.

END 6 Acknowledgements The author would like to thank Sean Olson for his comments. 7 Authors Addresses Jonathan Rosenberg dynamicsoft 72 Eagle Rock Avenue First Floor East Hanover, NJ 07936 email: jdrosen@dynamicsoft.com Henning Schulzrinne Columbia University M/S 0401 1214 Amsterdam Ave. New York, NY 10027-7003 email: schulzrinne@cs.columbia.edu 8 Normative References [1] A. Roach, "Session initiation protocol SIP specific event notification," RFC 3265, Internet Engineering Task Force, June 2002. [2] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: Session J. Rosenberg et. al. [Page 23] Internet Draft Dialog Package March 1, 2003 initiation protocol," RFC 3261, Internet Engineering Task Force, June 2002. [3] J. Rosenberg, "The session initiation protocol SIP update method," RFC 3311, Internet Engineering Task Force, Sept. 2002. [4] T. Bray, J. Paoli, and C. M. Sperberg-McQueen, "Extensible markup language (XML) 1.0 (second edition)," W3C Recommendation REC-xml- 20001006, World Wide Web Consortium (W3C), Oct. 2000. Available at http://www.w3.org/XML/. [5] R. Moats, "URN syntax," Request for Comments 2141, Internet Engineering Task Force, May 1997. [6] R. Moats, "A URN namespace for IETF documents," Request for Comments 2648, Internet Engineering Task Force, Aug. 1999. [7] M. Mealling, "The IETF XML registry," internet draft, Internet Engineering Task Force, July 2002. Work in progress. [8] M. Murata, S. S. Laurent, and D. Kohn, "XML media types," Request for Comments 3023, Internet Engineering Task Force, Jan. 2001. 9 Informative References [9] J. Rosenberg, "A presence event package for the session initiation protocol (SIP)," internet draft, Internet Engineering Task Force, Jan. 2003. Work in progress. [10] J. Rosenberg, "A watcher information event template-package for the session initiation protocol (SIP)," internet draft, Internet Engineering Task Force, Jan. 2003. Work in progress. [11] R. Mahy, "A message summary and message waiting indication event package for the session initiation protocol (SIP)," internet draft, Internet Engineering Task Force, Nov. 2002. Work in progress. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of J. Rosenberg et. al. [Page 24] Internet Draft Dialog Package March 1, 2003 claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright (c) The Internet Society (2003). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. J. Rosenberg et. al. [Page 25]