SIPPING J. Rosenberg Internet-Draft Cisco Systems Expires: October 11, 2005 H. Schulzrinne Columbia University R. Mahy, Ed. SIP Edge LLC Apr 12, 2005 An INVITE Inititiated Dialog Event Package for the Session Initiation Protocol (SIP) draft-ietf-sipping-dialog-package-06.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. 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. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 11, 2005. Copyright Notice Copyright (C) The Internet Society (2005). 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 Rosenberg, et al. Expires October 11, 2005 [Page 1] Internet-Draft Dialog Package Apr 2005 user, and receive notifications about the changes in state of INVITE initiated dialog usages that the user is involved in. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Dialog Event Package . . . . . . . . . . . . . . . . . . . . . 5 3.1 Event Package Name . . . . . . . . . . . . . . . . . . . . 5 3.2 Event Package Parameters . . . . . . . . . . . . . . . . . 5 3.3 SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . . 6 3.4 Subscription Duration . . . . . . . . . . . . . . . . . . 7 3.5 NOTIFY Bodies . . . . . . . . . . . . . . . . . . . . . . 7 3.6 Notifier Processing of SUBSCRIBE Requests . . . . . . . . 8 3.7 Notifier Generation of NOTIFY Requests . . . . . . . . . . 8 3.7.1 The Dialog State Machine . . . . . . . . . . . . . . . 9 3.7.2 Applying the state machine . . . . . . . . . . . . . . 12 3.8 Subscriber Processing of NOTIFY Requests . . . . . . . . . 13 3.9 Handling of Forked Requests . . . . . . . . . . . . . . . 13 3.10 Rate of Notifications . . . . . . . . . . . . . . . . . . 14 3.11 State Agents . . . . . . . . . . . . . . . . . . . . . . . 14 4. Dialog Information Format . . . . . . . . . . . . . . . . . . 14 4.1 Structure of Dialog Information . . . . . . . . . . . . . 14 4.1.1 Dialog Element . . . . . . . . . . . . . . . . . . . . 15 4.1.2 State . . . . . . . . . . . . . . . . . . . . . . . . 16 4.1.3 Duration . . . . . . . . . . . . . . . . . . . . . . . 16 4.1.4 Replaces . . . . . . . . . . . . . . . . . . . . . . . 16 4.1.5 Referred-By . . . . . . . . . . . . . . . . . . . . . 17 4.1.6 Local and Remote elements . . . . . . . . . . . . . . 17 4.1.6.1 Identity . . . . . . . . . . . . . . . . . . . . . 17 4.1.6.2 Target . . . . . . . . . . . . . . . . . . . . . . 17 4.1.6.3 Session Description . . . . . . . . . . . . . . . 18 4.2 Sample Notification Body . . . . . . . . . . . . . . . . . 19 4.3 Constructing Coherent State . . . . . . . . . . . . . . . 19 4.4 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5. Definition of new media feature parameters . . . . . . . . . . 23 5.1 The "sip.byeless" parameter . . . . . . . . . . . . . . . 23 5.2 The "sip.rendering" parameter . . . . . . . . . . . . . . 24 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 6.1 Basic Example . . . . . . . . . . . . . . . . . . . . . . 24 6.2 Emulating a Shared-Line phone system . . . . . . . . . . . 27 6.3 Minimal Dialog Information with Privacy . . . . . . . . . 31 7. Security Considerations . . . . . . . . . . . . . . . . . . . 32 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 8.1 application/dialog-info+xml MIME Registration . . . . . . 33 8.2 URN Sub-Namespace Registration for urn:ietf:params:xml:ns:dialog-info . . . . . . . . . . . . 33 8.3 Schema Registration . . . . . . . . . . . . . . . . . . . 34 Rosenberg, et al. Expires October 11, 2005 [Page 2] Internet-Draft Dialog Package Apr 2005 8.4 Media Feature Parameter Registration . . . . . . . . . . . 34 8.4.1 sip.byeless . . . . . . . . . . . . . . . . . . . . . 34 8.4.2 sip.rendering . . . . . . . . . . . . . . . . . . . . 35 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 36 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 36 10.1 Normative References . . . . . . . . . . . . . . . . . . . . 36 10.2 Informative References . . . . . . . . . . . . . . . . . . . 37 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 37 Intellectual Property and Copyright Statements . . . . . . . . 39 Rosenberg, et al. Expires October 11, 2005 [Page 3] Internet-Draft Dialog Package Apr 2005 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 [16], watcher information [17], and message waiting indicators [18], amongst others. Here, we define an event package for INVITE initiated dialog usages. 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 new dialog usages. However, the usage of this package to model transitions in the state of those dialog usages are out of the scope of this specification. There are a variety of applications enabled through the knowledge of INVITE dialog usage 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 subscribe 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 Instant Message (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. 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 Rosenberg, et al. Expires October 11, 2005 [Page 4] Internet-Draft Dialog Package Apr 2005 resides. In addition, this document also defines two new callee capabilities [10] feature parameters: "sip.byeless", which indicates that a SIP User Agent (UA) is not capable of terminating a session itself (for example as with some announcement or recording services, and in some call centers)in which the UA is no longer interested in participating; and "sip.rendering", which positively describes if the User Agent is rendering any of the media it is receiving. These feature parameters are useful in many of the same applications which motivated the dialog package, such as conferencing, presence, and the shared-line example described in Section 6.2. 2. Terminology In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [9] and indicate requirement levels for compliant implementations. 3. Dialog Event Package This section provides the details for defining a SIP Events package, as specified by [1]. 3.1 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]. 3.2 Event Package Parameters This package defines four Event Package parameters. They are call-id, to-tag, from-tag, and include-session-description. If a subscription to a specific dialog is requested, all of the first three of these parameters MUST be present. They identify the dialog 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. The include-session-description parameter indicates if the subscriber would like to receive the session descriptions associated with the subscribed dialog usage or usages. 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. Rosenberg, et al. Expires October 11, 2005 [Page 5] Internet-Draft Dialog Package Apr 2005 The ABNF for these parameters is shown below. It refers to many constructions from the ABNF of RFC3261, such as EQUAL, DQUOTE, and token. call-id = "call-id" EQUAL ( token / DQUOTE callid DQUOTE ) ;; NOTE: any DQUOTEs inside callid MUST be escaped! from-tag = "from-tag" EQUAL token to-tag = "to-tag" EQUAL token with-sessd = "include-session-description" Any callids which contain embedded double-quotes MUST escape those double-quotes using the backslash-quoting mechanism. Note that the call-id parameter may need to be expressed as a quoted string. This is because the ABNF for callid and word (which is used by callid) allow for some characters (such as "@", "[", and ":") which are not allowed within a token. 3.3 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 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 with the following exceptions. If the target (Contact) URI of a subscriber is equivalent to the remote target URI of a specific dialog, then the dialog element for that dialog is suppressed for that subscriber. (The subscriber is already a party in the dialog directly, so these notifications are superfluous.) If no dialogs remain after supressing dialogs, the entire notification to that subscriber is supressed and the version number in the dialog-info element is not incremented for that subscriber. Implicit filtering for one subscriber does not affect notifications to other subscribers. o Notifications do not normally contain full state; rather, they only indicate the state of the dialog whose state has changed. The exceptions are a NOTIFY sent in response to a SUBSCRIBE, and a NOTIFY that contains no dialog elements. These NOTIFYs contain Rosenberg, et al. Expires October 11, 2005 [Page 6] Internet-Draft Dialog Package Apr 2005 the complete view of dialog state. o The notifications contain the identities of the participants in the dialog, the target URIs, and the dialog identifiers. Session descriptions are not included normally unless explicitly requested and/or explicitly authorized. 3.4 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. Clients SHOULD 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. 3.5 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 Section 4. 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. Rosenberg, et al. Expires October 11, 2005 [Page 7] Internet-Draft Dialog Package Apr 2005 3.6 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 at least one call, or not. Specifically, they should not be able to find out any more information than if they sent an INVITE. (This concept of a "virtual" dialog is discussed more in Section 3.7.2, and an example of such a notification body is shown below.) confirmed 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. Note that many implementations of "shared-lines" have a feature which allows details of calls on a shared address-of-record to be made private. This is a completely reasonable authorization policy which could result in notifications which contain only the id attribute of the dialog element and the state element when shared-line privacy is requested, and notifications with more complete information when shared-line privacy is not requested. 3.7 Notifier Generation of NOTIFY Requests 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 Rosenberg, et al. Expires October 11, 2005 [Page 8] Internet-Draft Dialog Package Apr 2005 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 or participation information 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. 3.7.1 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. Rosenberg, et al. Expires October 11, 2005 [Page 9] Internet-Draft Dialog Package Apr 2005 +----------+ +----------+ | | 1xx-notag | | | |----------->| | | Trying | |Proceeding|-----+ | |---+ +-----| | | | | | | | | | +----------+ | | +----------+ | | | | | | | | | | | | | +<--C-----C--+ |1xx-tag | | | | | | cancelled| | | V | rejected| | |1xx-tag +----------+ | | | +------->| | |2xx | | | | | +<--C--------------| Early |-----C---+ 1xx-tag | | replaced | | | | w/new tag | | | |<----C---+ (new FSM | | +----------+ | instance | | 2xx | | created) | +----------------+ | | | | |2xx | | | | | V V V | +----------+ +----------+ | | | | | | | | | | | |Terminated|<-----------| Confirmed|<----+ | | error | | | | timeout | | +----------+ replaced +----------+ local-bye | ^ remote-bye | | | | +------+ 2xx w. new tag (new FSM instance created) Figure 3 The FSM for dialog state is shown in Figure 3. 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 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", Rosenberg, et al. Expires October 11, 2005 [Page 10] Internet-Draft Dialog Package Apr 2005 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 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 UAC receives a new invitation (with a Replaces [13] header) which replaces the current Early or Confirmed dialog, all INVITE transactions spawned from the replaced invitation transition to the "terminated" state with the event "replaced". 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 "local-bye" and "remote-bye" events as appropriate), 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". If the UAS receives a new invitation (with a Replaces [13] header) which replaces the current Confirmed dialog, the replaced invitation transitions to the "terminated" state with the event "replaced". Once in the "confirmed" state, the other transitions to the "terminated" state occur for the same reasons they do in the case of UAC. Rosenberg, et al. Expires October 11, 2005 [Page 11] Internet-Draft Dialog Package Apr 2005 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. 3.7.2 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 is RECOMMENDED that subscriptions to an individual dialog, or to a specific set of dialogs, is forbidden. Only subscriptions to all dialogs (i.e., there are no dialog identifiers in the Event header field) are permitted. In that case, actual dialog states across all dialogs will 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 know 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 (as shown in the example in Section 3.6. 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. Rosenberg, et al. Expires October 11, 2005 [Page 12] Internet-Draft Dialog Package Apr 2005 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 SHOULD generate a NOTIFY request on any change in the characteristics associated with the dialog. Since these include Contact URIs, Contact parameters and session descriptions, receipt of re-INVITEs and UPDATE requests [3] which modify this information MAY trigger notifications. 3.8 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 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 4.3 for information on constructing coherent information from an application/dialog-info+xml document. 3.9 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. Rosenberg, et al. Expires October 11, 2005 [Page 13] Internet-Draft Dialog Package Apr 2005 3.10 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 1 second. 3.11 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. However, in some cases, a network agent may also know the state of the dialogs held by a user. As such, state agents MAY be used with this package. 4. 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: urn:ietf:params:xml:ns:dialog-info A dialog information document begins with the root element tag "dialog-info". 4.1 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. This user is referred to as the "observed user". The dialog-info element has a series of zero or more dialog Rosenberg, et al. Expires October 11, 2005 [Page 14] Internet-Draft Dialog Package Apr 2005 sub-elements. Each of those represents a specific dialog. 4.1.1 Dialog Element The dialog element reports information on a specific dialog or "half-dialog". It has 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. 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. (Note that single and double quotes inside a call-id must be escaped using "e; for " and ' for ' .) 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 observed user was the initiator of the dialog, or the recipient of the INVITE that created it. Rosenberg, et al. Expires October 11, 2005 [Page 15] Internet-Draft Dialog Package Apr 2005 ... The sub-elements of the dialog element provide additional information about the dialog. Some of these sub-elements provide more detail about the dialog itself, while the local and remote sub-elements describe characteristics of the participants involved in the dialog. The only mandatory sub-element is the state element. 4.1.2 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 any transition into the terminated state, and an optional code attribute that indicates the response code associated with any transition caused by a response to the original INVITE. terminated 4.1.3 Duration The duration element contains the amount of time, in seconds, since the FSM was created. 145 4.1.4 Replaces The replaces element is used to correlate a new dialog with one it replaced as a result of an invitation with a Replaces header. This element is present in the replacement dialog only (the newer dialog) and contains attributes with the call-id, local-tag, and remote-tag of the replaced dialog. Rosenberg, et al. Expires October 11, 2005 [Page 16] Internet-Draft Dialog Package Apr 2005 4.1.5 Referred-By The referred-by element is used to correlate a new dialog with a REFER [12] request which triggered it. The element is present in a dialog which was triggered by a REFER request which contained a Referred-By [11] header and contains the (optional) display name attribute and the Referred-By URI as its value. sip:bob@example.com 4.1.6 Local and Remote elements The local and remote elements are sub-elements of the dialog element which contain information about the local and remote participants respectively. They both have a number of optional sub-elements which indicate the identity conveyed by the participant, the target URI, the feature-tags of the target, and the session-description of the participant. 4.1.6.1 Identity The identity element indicates a local or remote URI, as defined in [2] as appropriate. It has an optional attribute, display, that contains the display name from the appropriate URI. Note that multiple identities (for example a sip: URI and a tel: URI) could be included if they all correspond to the participant. To avoid repeating identity information in each request, the subscriber can assume that the identity URIs are the same as in previous notifications if no identity elements are present in the corresponding local or remote element. If any identity elements are present in the local or remote part of a notification, the new list of identity tags completely supersedes the old list in the corresponding part. sip:anonymous@anonymous.invalid 4.1.6.2 Target The target contains the local or remote target URI as constructed by the user agent for this dialog, as defined in RFC 3261 [2] in a "uri" attribute. It can contain a list of Contact header parameters in param sub-elements (such as those defined in [10]). The param element contains two required attributes, pname and pval. Boolean parameters are represented by the explicit pval values "true" and "false" (for example when a feature parameter is explicitly negated). The param Rosenberg, et al. Expires October 11, 2005 [Page 17] Internet-Draft Dialog Package Apr 2005 element itself has no contents. To avoid repeating Contact information in each request, the subscriber can assume that the target URI and parameters are the same as in previous notifications if no target element is present in the corresponding local or remote element. If a target element is present in the local or remote part of a notification, the new target tag and list of an parameter tags completely supersedes the old target and parameter list in the corresponding part. 4.1.6.3 Session Description The session-description element contains the session description used by the observed user 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. To avoid repeating session description information in each request, the subscriber can assume that the session description is the same as in previous notifications if no session description element is present in the corresponding local or remote element. Rosenberg, et al. Expires October 11, 2005 [Page 18] Internet-Draft Dialog Package Apr 2005 4.2 Sample Notification Body confirmed 274 sip:alice@example.com sip:bob@example.org 4.3 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" 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, Rosenberg, et al. Expires October 11, 2005 [Page 19] Internet-Draft Dialog Package Apr 2005 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. 4.4 Schema The following is the schema for the application/dialog-info+xml type: Rosenberg, et al. Expires October 11, 2005 [Page 20] Internet-Draft Dialog Package Apr 2005 Rosenberg, et al. Expires October 11, 2005 [Page 21] Internet-Draft Dialog Package Apr 2005 Rosenberg, et al. Expires October 11, 2005 [Page 22] Internet-Draft Dialog Package Apr 2005 5. Definition of new media feature parameters This section defines two new media feature parameters which are useful as input to user presence, in conferencing applications, and in applications like the shared-line example described in Section 6.2. These feature parameters are especially useful when used in combination with the dialog package, as they allow an authorized third party to become aware of these characteristics. 5.1 The "sip.byeless" parameter The "sip.byeless" media feature parameter is a new boolean parameter, defined in this document, which provides a positive indication that the User Agent setting the parameter is unable to terminate sessions on its own (for example, by sending a BYE request). For example, Rosenberg, et al. Expires October 11, 2005 [Page 23] Internet-Draft Dialog Package Apr 2005 continuous announcement services and certain recording services are unable to determine when it would be desirable to terminate a session and therefore do not have the ability to terminate sessions at all. Also, many human call centers are configured so that they never terminate sessions. (This is to prevent call center agents from accidentally disconnecting the caller.) Contact: ;automaton;+sip.byeless 5.2 The "sip.rendering" parameter The "sip.rendering" media feature parameter is a new string parameter, defined in this document, which can provide a positive indication whether the User Agent setting the parameter is currently rendering any of the media it is receiving in the context of a specific session. It MUST only be used in a Contact header field in a dialog created using the INVITE request. (Note that per [10] this parameter name must be preceeded by a "+" character when used in a SIP Contact header field.) This parameter has three legal values: "yes", "no", and "unknown". The value "yes" indicates positive knowledge that the User Agent is rendering at least one of the streams of media that it is receiving. The value "no" indicates positive knowledge that the User Agent is rendering none of the media that it is receiving. The value "unknown" indicates that the User Agent does not know whether the media associated with the session is being rendered. (which may be the case if the User Agent is acting as a 3pcc (Third Party Call Control) [19] controller). The "sip.rendering" parameter is useful in applications such as shared appearances, conference status monitoring, or as an input to user presence. Contact: ;automaton;+sip.rendering="no" 6. Examples 6.1 Basic Example For example, if a UAC sends an INVITE that looks like, in part: Rosenberg, et al. Expires October 11, 2005 [Page 24] Internet-Draft Dialog Package Apr 2005 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: 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: Rosenberg, et al. Expires October 11, 2005 [Page 25] Internet-Draft Dialog Package Apr 2005 early If it receives a second 180 with a different tag: 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: Rosenberg, et al. Expires October 11, 2005 [Page 26] Internet-Draft Dialog Package Apr 2005 confirmed 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 6.2 Emulating a Shared-Line phone system The following example shows how a SIP telephone user agent can provide detailed state information and also emulate a shared-line telephone system (the phone "lies" about having a dialog while it is merely offhook). Idle: Seized: Rosenberg, et al. Expires October 11, 2005 [Page 27] Internet-Draft Dialog Package Apr 2005 trying Dialing: trying sip:alice@example.com sip:bob@example.net Ringing: early Answered (by voicemail): Rosenberg, et al. Expires October 11, 2005 [Page 28] Internet-Draft Dialog Package Apr 2005 terminated confirmed Alice requests voicemail for Bob's attendant. (Alice presses "0" in North America / "9" in Europe) Voicemail completes a transfer with Cathy terminated confirmed sip:bob-is-not-here@vm.example.net Rosenberg, et al. Expires October 11, 2005 [Page 29] Internet-Draft Dialog Package Apr 2005 sip:cjones@example.net Alice and Cathy talk, Cathy adds Alice to a local conference. confirmed Alice puts Cathy on hold confirmed Rosenberg, et al. Expires October 11, 2005 [Page 30] Internet-Draft Dialog Package Apr 2005 Cathy hangs up terminated trying Alice hangs up: 6.3 Minimal Dialog Information with Privacy The following example shows the same user agent providing minimal information to maintain privacy for services like automatic callback. Rosenberg, et al. Expires October 11, 2005 [Page 31] Internet-Draft Dialog Package Apr 2005 Onhook: Offhook: (implementation/policy choice for Alice to transition to this "state" when "seized", when Trying, when Proceeding, or when Confirmed.) confirmed Onhook: (implementation/policy choice for Alice to transition to this "state" when terminated, or when no longer "seized") 7. Security Considerations Subscriptions to dialog state can reveal sensitive information. For this reason, Section 3.6 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. User Agents that implement the dialog package SHOULD also implement SIP over TLS [15] and the sips: scheme. 8. IANA Considerations This document registers a new MIME type, application/dialog-info+xml; Rosenberg, et al. Expires October 11, 2005 [Page 32] Internet-Draft Dialog Package Apr 2005 a new XML namespace; and two new media feature parameters in the SIP tree. 8.1 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 application/xml as specified in RFC 3023 [8]. Security considerations: See Section 10 of RFC 3023 [8] and Section 7 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: .xml Macintosh file type code: "TEXT" Personal and email address for further information: Jonathan Rosenberg, Intended usage: COMMON Author/Change controller: The IETF. 8.2 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: The IESG, XML: Rosenberg, et al. Expires October 11, 2005 [Page 33] Internet-Draft Dialog Package Apr 2005 BEGIN Dialog Information Namespace

Namespace for Dialog Information

urn:ietf:params:xml:ns:dialog-info

See RFCXXXX.

END 8.3 Schema Registration This specification registers a schema, as per the guidelines in in [7]. URI: please assign. Registrant Contact: The IESG, XML: The XML can be found as the sole content of Section 4.4. 8.4 Media Feature Parameter Registration This section registers two new media feature tags, per the procedures defined in RFC 2506 [14]. The tags are placed into the sip tree, which is defined in [10]. 8.4.1 sip.byeless Media feature tag name sip.byeless ASN.1 Identifier New assignment by IANA. Summary of the media feature indicated by this tag This feature tag is a boolean flag. When set it indicates that the device is incapable of terminating a session autonomously. Values appropriate for use with this feature tag Boolean. The feature tag is intended primarily for use in the following applications, protocols, services, or negotiation mechanisms This feature tag is most useful in a communications application for describing the capabilities of an application, such as an announcement service, recording service, conference, or call center. Rosenberg, et al. Expires October 11, 2005 [Page 34] Internet-Draft Dialog Package Apr 2005 Examples of typical use Call centers and media services. Related standards or documents RFC XXXX [[Note to IANA: Please replace XXXX with the RFC number of this specification.]] Security Considerations This media feature tag can be used in ways which affect application behaviors or may reveal private information. For example, a conferencing or other application may decide to terminate a call prematurely if this media feature tag is set. Therefore, if an attacker can modify the values of this tag, they may be able to affect the behavior of applications. As a result of this, applications which utilize this media feature tag SHOULD provide a means for ensuring its integrity. Similarly, this feature tag should only be trusted as valid when it comes from the user or user agent described by the tag. As a result, protocols for conveying this feature tag SHOULD provide a mechanism for guaranteeing authenticity. 8.4.2 sip.rendering Media feature tag name sip.rendering ASN.1 Identifier New assignment by IANA. Summary of the media feature indicated by this tag This feature tag contains one of three string values indicating if the device is rendering any media from the current session ("yes"), none of the media from the current session ("no"), or if this status is not known to the device ("unknown"). Values appropriate for use with this feature tag String. The feature tag is intended primarily for use in the following applications, protocols, services, or negotiation mechanisms This feature tag is most useful in a communications application, for describing the state of a device (such as a phone or PDA) during a multimedia session. Examples of typical use Conferencing, telephone shared-line emulation, and presence applications. Related standards or documents RFC XXXX [[Note to IANA: Please replace XXXX with the RFC number of this specification.]] Security Considerations This media feature tag can be used in ways which affect application behaviors or may reveal private information. For exmaple, a conferencing or other application may decide to terminate a call prematurely if this media feature tag is set to "no". Therefore, if an attacker can modify the values of this tag, they may be able to affect the behavior of applications. As a result of this, applications which utilize this media feature tag SHOULD provide a means for ensuring its integrity. Similarly, this feature tag should only be trusted as valid when it comes from the user or user agent described by the tag. As a result, protocols for conveying this feature tag SHOULD provide a mechanism for guaranteeing authenticity. Rosenberg, et al. Expires October 11, 2005 [Page 35] Internet-Draft Dialog Package Apr 2005 9. Acknowledgements The authors would like to thank Sean Olson for his comments. 10. References 10.1 Normative References [1] Roach, A., "Session Initiation Protocol (SIP)-Specific Event Notification", RFC 3265, June 2002. [2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [3] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE Method", RFC 3311, October 2002. [4] Paoli, J., Sperberg-McQueen, C., Bray, T. and E. Maler, "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C FirstEdition REC-xml-20001006, October 2000. [5] Moats, R., "URN Syntax", RFC 2141, May 1997. [6] Moats, R., "A URN Namespace for IETF Documents", RFC 2648, August 1999. [7] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. [8] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC 3023, January 2001. [9] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [10] Rosenberg, J., Schulzrinne, H. and P. Kyzivat, "Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)", RFC 3840, August 2004. [11] Sparks, R., "The Session Initiation Protocol (SIP) Referred-By Mechanism", RFC 3892, September 2004. [12] Sparks, R., "The Session Initiation Protocol (SIP) Refer Method", RFC 3515, April 2003. [13] Mahy, R., Biggs, B. and R. Dean, "The Session Initiation Protocol (SIP) "Replaces" Header", RFC 3891, September 2004. Rosenberg, et al. Expires October 11, 2005 [Page 36] Internet-Draft Dialog Package Apr 2005 [14] Holtman, K., Mutz, A. and T. Hardie, "Media Feature Tag Registration Procedure", BCP 31, RFC 2506, March 1999. [15] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. 10.2 Informative References [16] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", RFC 3856, August 2004. [17] Rosenberg, J., "A Watcher Information Event Template-Package for the Session Initiation Protocol (SIP)", RFC 3857, August 2004. [18] Mahy, R., "A Message Summary and Message Waiting Indication Event Package for the Session Initiation Protocol (SIP)", RFC 3842, August 2004. [19] Rosenberg, J., Peterson, J., Schulzrinne, H. and G. Camarillo, "Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April 2004. [20] Rosenberg, J., "Obtaining and Using Globally Routable User Agent (UA) URIs (GRUU) in the Session Initiation Protocol (SIP)", draft-ietf-sip-gruu-03 (work in progress), February 2005. [21] Sparks, R. and A. Johnston, "Session Initiation Protocol Call Control - Transfer", draft-ietf-sipping-cc-transfer-03 (work in progress), October 2004. Authors' Addresses Jonathan Rosenberg Cisco Systems 600 Lanidex Plaza Parsippany, NJ 07054 US Phone: +1 973 952-5000 EMail: jdrosen@cisco.com URI: http://www.jdrosen.net Rosenberg, et al. Expires October 11, 2005 [Page 37] Internet-Draft Dialog Package Apr 2005 Henning Schulzrinne Columbia University M/S 0401 1214 Amsterdam Ave. New York, NY 10027 US EMail: schulzrinne@cs.columbia.edu URI: http://www.cs.columbia.edu/~hgs Rohan Mahy (editor) SIP Edge LLC EMail: rohan@ekabal.com Rosenberg, et al. Expires October 11, 2005 [Page 38] Internet-Draft Dialog Package Apr 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights 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; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Rosenberg, et al. Expires October 11, 2005 [Page 39]