SIPPING J. Rosenberg
Internet-Draft dynamicsoft
Expires: April 24, 2004 H. Schulzrinne
Columbia University
R. Mahy, Ed.
Cisco Systems, Inc.
October 25, 2003
An INVITE Inititiated Dialog Event Package for the Session
Initiation Protocol (SIP)
draft-ietf-sipping-dialog-package-03.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . 4
3. Dialog Event Package . . . . . . . . . . . . . . . . . . 4
3.1 Event Package Name . . . . . . . . . . . . . . . . . . . 4
3.2 Event Package Parameters . . . . . . . . . . . . . . . . 4
3.3 SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . 5
3.4 Subscription Duration . . . . . . . . . . . . . . . . . 6
3.5 NOTIFY Bodies . . . . . . . . . . . . . . . . . . . . . 6
3.6 Notifier Processing of SUBSCRIBE Requests . . . . . . . 6
3.7 Notifier Generation of NOTIFY Requests . . . . . . . . . 7
3.7.1 The Dialog State Machine . . . . . . . . . . . . . . . . 8
3.7.2 Applying the state machine . . . . . . . . . . . . . . . 10
3.8 Subscriber Processing of NOTIFY Requests . . . . . . . . 12
3.9 Handling of Forked Requests . . . . . . . . . . . . . . 12
3.10 Rate of Notifications . . . . . . . . . . . . . . . . . 12
3.11 State Agents . . . . . . . . . . . . . . . . . . . . . . 13
4. Dialog Information Format . . . . . . . . . . . . . . . 13
4.1 Structure of Dialog Information . . . . . . . . . . . . 13
4.1.1 Dialog Element . . . . . . . . . . . . . . . . . . . . . 14
4.1.2 State . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1.3 Duration . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1.4 Replaces . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1.5 Referred-By . . . . . . . . . . . . . . . . . . . . . . 16
4.1.6 Route-Set . . . . . . . . . . . . . . . . . . . . . . . 16
4.1.6.1 Local and Remote elements . . . . . . . . . . . . . . . 16
4.1.6.1.1 Identity . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1.6.1.2 Target . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.1.6.1.3 Session Description . . . . . . . . . . . . . . . . . . 17
4.1.6.1.4 CSeq . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.2 Constructing Coherent State . . . . . . . . . . . . . . 17
4.3 Schema . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.4 Example . . . . . . . . . . . . . . . . . . . . . . . . 21
5. Security Considerations . . . . . . . . . . . . . . . . 25
6. IANA Considerations . . . . . . . . . . . . . . . . . . 25
6.1 application/dialog-info+xml MIME Registration . . . . . 25
6.2 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:dialog-info . . . . . . . . . . . 26
6.3 Schema Registration . . . . . . . . . . . . . . . . . . 26
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . 27
Normative References . . . . . . . . . . . . . . . . . . 27
Informative References . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . 28
Intellectual Property and Copyright Statements . . . . . 30
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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 [14], watcher
information [15], and message waiting indicators [16], 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.
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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. 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 or
dialogs.
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 ABNF for these parameters is shown below. It refers to many
constructions from the ABNF of RFC3261, such as word, callid, 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
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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
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, CSeq numbers, SDP information, and so on,
are not included normally unless explicitly requested and/or
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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.
3.6 Notifier Processing of SUBSCRIBE Requests
The dialog information for a user contains sensitive information.
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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.)
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="0" state="full"
entity="sip:alice@example.com">
<dialog id="as7d900as8">
<state>confirmed</state>
</dialog>
</dialog-info>
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
precisely when to send notifications, and what their content should
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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.
+----------+ +----------+
| | 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
| | 2xx | | instance
| +----------------+ | | created)
| | |2xx |
| | | |
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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",
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
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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 transition 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.
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.
OPEN ISSUE: Since there is only one possible event to cause
transitions to the Proceeding (1xx-notag), Early (1xx-tag), and
Confirmed (2xx) states, the only events which provide any
additional information are the events for transitions to
Terminated (error, timeout, cancelled, local-bye, remote-bye and
replaced). Of these, timeout may not be relevant, since it is
often indistinguishable from "rejected" (for example, a 408) or
"error". Likewise it is unclear if there is any value in
distinguishing "local-bye" from "cancelled"; perhaps we should use
a single event, such as "local-hangup" instead.
3.7.2 Applying the state machine
The notifier MAY generate a NOTIFY request on any event transition of
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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 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.
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
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numbers and SDP, receipt of re-INVITEs and UPDATE requests [3] which
modify this information MAY trigger notifications.
OPEN ISSUE: Is there a good reason to include CSeqs at all? Can
anyone come up with a use case? This seems to contradict the
"Rate of Notifications" section, and I can come up with some good
examples where this would be VERY BAD. For example, say Alice
sends an invitation to Bob, and then, on the same dialog,
subscribes to his dialog package, requesting CSeq information.
Every notification updates the CSeq which in turn generates
another notification, causing an infinite flood of messages.
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 4.2 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.
3.10 Rate of Notifications
For reasons of congestion control, it is important that the rate of
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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.
Editors Note: This seems too slow to me. I think 1 second is
probably reasonable.
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).
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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
sub-elements. Each of those represents a specific dialog.
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="0" state="full"
entity="sip:alice@example.com">
</dialog-info>
4.1.1 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.
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 ' .)
OPEN ISSUE: Is it legal to include escaped quotes in XML
attributes?
local-tag: This attribute is a string which represents the local-tag
component of the dialog identifier.
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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.
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="0" state="partial"
entity="sip:alice@example.com">
<dialog id="as7d900as8" call-id="a84b4c76e66710"
local-tag="1928301774" direction="initiator">
...
</dialog>
</dialog-info>
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.
<state event="rejected" code="486">terminated</state>
4.1.3 Duration
The duration element contains the amount of time, in seconds, since
the FSM was created.
<duration>145</duration>
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)
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and contains attributes with the call-id, local-tag, and remote-tag
of the replaced dialog.
<replaces call-id="hg287s98s89" local-tag="6762h7" remote-tag="09278hsb"/>
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.
<referred-by display="Bob">sip:bob@example.com</referred-by>
4.1.6 Route-Set
The route-set element conveys an ordered list of hop elements which
represents the complete route set of the dialog (not including the
local and remote target URIs) from the perspective of the notifier.
OPEN ISSUE: Does any one want/need this?
<route-set>
<hop>sip:proxy1.example.net;lr</hop>
<hop>sip:proxy2.example.com;lr</hop>
</route-set>
4.1.6.1 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.
4.1.6.1.1 Identity
The identity element indicates a local or remote URI, as defined in
[2] as appropriate. It has an optional attribute, display-name, 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.
<identity display="Anonymous">sip:anonymous@anonymous.invalid</identity>
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4.1.6.1.2 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 a required pname attribute and an optional pval attribute
(some parameters merely exist and have no explicit value). The param
element itself has no contents.
<target uri="sip:alice@pc33.example.com">
<param pname="isfocus"/>
<param pname="class" pval="personal"/>
</target>
4.1.6.1.3 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.
4.1.6.1.4 CSeq
The 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.
OPEN ISSUE: Is this really useful?
4.2 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"
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
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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.
4.3 Schema
The following is the schema for the application/dialog-info+xml type:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
targetNamespace="urn:ietf:params:xml:ns:dialog-info"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:tns="urn:ietf:params:xml:ns:dialog-info"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- This import brings in the XML language attribute xml:lang-->
<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/03/xml.xsd"/>
<xs:element name="dialog-info">
<xs:complexType>
<xs:sequence>
<xs:element ref="tns:dialog" minOccurs="0"
maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
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</xs:sequence>
<xs:attribute name="version" type="xs:nonNegativeInteger"
use="required"/>
<xs:attribute name="state" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="full"/>
<xs:enumeration value="partial"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="entity" type="xs:anyURI" use="required"/>
</xs:complexType>
</xs:element>
<xs:element name="dialog">
<xs:complexType>
<xs:sequence>
<xs:element ref="tns:state" minOccurs="1" maxOccurs="1"/>
<xs:element name="duration" type="xs:nonNegativeInteger"
minOccurs="0" maxOccurs="1"/>
<xs:element name="replaces" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:attribute name="call-id" type="xs:string"
use="required"/>
<xs:attribute name="local-tag" type="xs:string"
use="required"/>
<xs:attribute name="remote-tag" type="xs:string"
use="required"/>
</xs:complexType>
</xs:element>
<xs:element name="referred-by" type="tns:nameaddr"
minOccurs="0" maxOccurs="1"/>
<xs:element name="route-set" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:sequence>
<xs:element name="hop" type="xs:string" minOccurs="1"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="local" type="tns:participant"
minOccurs="0" maxOccurs="1"/>
<xs:element name="remote" type="tns:participant"
minOccurs="0" maxOccurs="1"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="id" type="xs:string" use="required"/>
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<xs:attribute name="call-id" type="xs:string"
use="optional"/>
<xs:attribute name="local-tag" type="xs:string"
use="optional"/>
<xs:attribute name="remote-tag" type="xs:string"
use="optional"/>
<xs:attribute name="direction" use="optional">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="initiator"/>
<xs:enumeration value="recipient"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:complexType name="participant">
<xs:sequence>
<xs:element name="identity" type="nameaddr"
minOccurs="0" maxOccurs="1"/>
<xs:element name="target" minOccurs="0" maxOccurs="1">
<xs:complexType>
<xs:sequence>
<xs:element name="param" minOccurs="0"
maxOccurs="unbounded">
<xs:complexType>
<xs:attribute name="pname" type="xs:string"
use="required"/>
<xs:attribute name="pval" type="xs:string"
use="optional"/>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
<xs:attribute name="uri" type="xs:string" use="required"/>
</xs:element>
<xs:element name="session-description" type="tns:sessd"
minOccurs="0" maxOccurs="1"/>
<xs:element name="cseq" type="xs:nonNegativeInteger"
minOccurs="0" maxOccurs="1"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="nameaddr">
<xs:simpleContent>
<xs:extension base="xs:anyURI">
<xs:attribute name="display-name" type="xs:string"
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use="optional"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:complexType name="sessd">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="type" type="xs:string" use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:element name="state">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="event" use="optional">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="cancelled"/>
<xs:enumeration value="rejected"/>
<xs:enumeration value="replaced"/>
<xs:enumeration value="local-bye"/>
<xs:enumeration value="remote-bye"/>
<xs:enumeration value="error"/>
<xs:enumeration value="timeout"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="code" use="optional">
<xs:simpleType>
<xs:restriction base="xs:positiveInteger">
<xs:minInclusive value="100"/>
<xs:maxInclusive value="699"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:schema>
4.4 Example
For example, if a UAC sends an INVITE that looks like, in part:
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INVITE sip:bob@example.com SIP/2.0
Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8
Max-Forwards: 70
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@example.com>;tag=1928301774
Call-ID: a84b4c76e66710
CSeq: 314159 INVITE
Contact: <sip:alice@pc33.example.com>
Content-Type: application/sdp
Content-Length: 142
[SDP not shown]
The XML document in a notification from Alice might look like:
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="0"
state="full"
entity="sip:alice@example.com">
<dialog id="as7d900as8" call-id="a84b4c76e66710"
local-tag="1928301774" direction="initiator">
<state>trying</state>
</dialog>
</dialog-info>
If the following 180 response is received:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8
To: Bob <sip:bob@example.com>;tag=456887766
From: Alice <sip:alice@example.com>;tag=1928301774
Call-ID: a84b4c76e66710
CSeq: 314159 INVITE
Contact: <sip:bob@host.example.com>
The XML document in a notification might look like:
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="1"
state="full"
entity="sip:alice@example.com">
<dialog id="as7d900as8" call-id="a84b4c76e66710"
local-tag="1928301774" remote-tag="456887766"
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direction="initiator">
<state>early</state>
</dialog>
</dialog-info>
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 <sip:bob@example.com>;tag=hh76a
From: Alice <sip:alice@example.com>;tag=1928301774
Call-ID: a84b4c76e66710
CSeq: 314159 INVITE
Contact: <sip:jack@host.example.com>
This results in the creation of a second dialog:
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="2"
state="full"
entity="sip:alice@example.com">
<dialog id="as7d900as8" call-id="a84b4c76e66710"
local-tag="1928301774" remote-tag="456887766"
direction="initiator">
<state>early</state>
</dialog>
<dialog id="as7d900as8" call-id="a84b4c76e66710"
local-tag="1928301774" remote-tag="hh76a"
direction="initiator">
<state>early</state>
</dialog>
</dialog-info>
If a 200 OK is received on the second dialog, it moves to confirmed:
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="3"
state="partial"
entity="sip:alice@example.com">
<dialog id="as7d900as8" call-id="a84b4c76e66710"
local-tag="1928301774" remote-tag="hh76a"
direction="initiator">
<state>confirmed</state>
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</dialog>
</dialog-info>
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:
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="4"
state="partial"
entity="sip:alice@example.com">
<dialog id="as7d900as8" call-id="a84b4c76e66710"
local-tag="1928301774" remote-tag="hh76a"
direction="initiator">
<state event="cancelled">terminated</state>
</dialog>
</dialog-info>
EDITORS NOTE: should provide another example with a richer
notification
<?xml version="1.0" encoding="UTF-8"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:dialog-info"
version="1" state="full">
<dialog id="123456">
<state>confirmed</state>
<duration>274</duration>
<local>
<identity display="Alice">sip:alice@example.com</identity>
<target uri="sip:alice@pc33.example.com">
<param pname="isfocus"/>
<param pname="class" pval="personal"/>
</target>
</local>
<remote>
<identity display="Bob">sip:bob@example.org</identity>
<target uri="sip:bobster@phone21.example.org"/>
</remote>
</dialog>
</dialog-info>
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5. 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.
6. IANA Considerations
This document registers a new MIME type, application/dialog-info+xml
and registers a new XML namespace.
6.1 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 5
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
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Macintosh file type code: "TEXT"
Personal and email address for further information: Jonathan
Rosenberg, <jdrosen@jdrosen.net>
Intended usage: COMMON
Author/Change controller: The IETF.
6.2 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, SIPPING working group, <sipping@ietf.org>,
Jonathan Rosenberg <jdrosen@jdrosen.net>.
XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Dialog Information Namespace</title>
</head
<body>
<h1>Namespace for Dialog Information</h1>
<h2>urn:ietf:params:xml:ns:dialog-info</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
6.3 Schema Registration
This specification registers a schema, as per the guidelines in in
[7].
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URI: please assign.
Registrant Contact: IETF, SIPPING Working Group
(sipping@ietf.org), Jonathan Rosenberg (jdrosen@jdrosen.net).
XML: The XML can be found as the sole content of Section 4.3.
7. Acknowledgements
The authors would like to thank Sean Olson for his comments.
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] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
REC 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",
draft-mealling-iana-xmlns-registry-04 (work in progress), July
2002.
[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., "Indicating User Agent Capabilities in the
Session Initiation Protocol (SIP)",
draft-ietf-sip-callee-caps-00 (work in progress), June 2003.
[11] Sparks, R., "The SIP Referred-By Mechanism",
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draft-ietf-sip-referredby-01 (work in progress), February 2003.
[12] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[13] Dean, R., Biggs, B. and R. Mahy, "The Session Inititation
Protocol (SIP) 'Replaces' Header", draft-ietf-sip-replaces-03
(work in progress), March 2003.
Informative References
[14] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", draft-ietf-simple-presence-10 (work
in progress), January 2003.
[15] Rosenberg, J., "A Watcher Information Event Template-Package
for the Session Initiation Protocol (SIP)",
draft-ietf-simple-winfo-package-05 (work in progress), January
2003.
[16] Mahy, R., "A Message Summary and Message Waiting Indication
Event Package for the Session Initiation Protocol (SIP)",
draft-ietf-sipping-mwi-02 (work in progress), March 2003.
Authors' Addresses
Jonathan Rosenberg
dynamicsoft
600 Lanidex Plaza
Parsippany, NJ 07054
US
Phone: +1 973 952-5000
EMail: jdrosen@dynamicsoft.com
URI: http://www.jdrosen.net
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
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Rohan Mahy (editor)
Cisco Systems, Inc.
5617 Scotts Valley Dr
Scotts Valley, CA 95066
USA
EMail: rohan@cisco.com
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