draft-ietf-sip-events-02.txt   draft-ietf-sip-events-03.txt 
Internet Engineering Task Force Adam Roach Internet Engineering Task Force Adam Roach
Internet Draft dynamicsoft Internet Draft dynamicsoft
Category: Standards Track February 2002 Category: Standards Track February 2002
Expires August 2002 Expires August 2002
<draft-ietf-sip-events-02.txt> <draft-ietf-sip-events-03.txt>
SIP-Specific Event Notification SIP-Specific Event Notification
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026. with all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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Note that the event notification mechanisms defined herein are Note that the event notification mechanisms defined herein are
NOT intended to be a general-purpose infrastructure for all NOT intended to be a general-purpose infrastructure for all
classes of event subscription and notification. classes of event subscription and notification.
1. Table of Contents 1. Table of Contents
1. Table of Contents...................................... 1 1. Table of Contents...................................... 1
2. Introduction........................................... 3 2. Introduction........................................... 3
2.1. Overview of Operation.................................. 4 2.1. Overview of Operation.................................. 4
3. Definitions............................................ 4 2.2. Documentation Conventions.............................. 4
3. Definitions............................................ 5
4. Node Behavior.......................................... 5 4. Node Behavior.......................................... 5
4.1. Description of SUBSCRIBE Behavior...................... 5 4.1. Description of SUBSCRIBE Behavior...................... 5
4.1.1. Subscription duration.................................. 5 4.1.1. Subscription Duration.................................. 6
4.1.2. Identification of Subscribed Events and Event Classes.. 6 4.1.2. Identification of Subscribed Events and Event Classes.. 6
4.1.3. Additional SUBSCRIBE Header Values..................... 6 4.1.3. Additional SUBSCRIBE Header Values..................... 7
4.1.4. Subscriber SUBSCRIBE Behavior.......................... 7 4.1.4. Subscriber SUBSCRIBE Behavior.......................... 7
4.1.5. Proxy SUBSCRIBE Behavior............................... 8 4.1.5. Proxy SUBSCRIBE Behavior............................... 9
4.1.6. Notifier SUBSCRIBE Behavior............................ 9 4.1.6. Notifier SUBSCRIBE Behavior............................ 9
4.2. Description of NOTIFY Behavior......................... 11 4.2. Description of NOTIFY Behavior......................... 12
4.2.1. Identification of reported events, event classes, and c 12 4.2.1. Identification of Reported Events, Event Classes, and C 12
4.2.2. Notifier NOTIFY Behavior............................... 12 4.2.2. Notifier NOTIFY Behavior............................... 13
4.2.3. Proxy NOTIFY Behavior.................................. 14 4.2.3. Proxy NOTIFY Behavior.................................. 15
4.2.4. Subscriber NOTIFY Behavior............................. 14 4.2.4. Subscriber NOTIFY Behavior............................. 15
4.3. General................................................ 16 4.3. General................................................ 17
4.3.1. Detecting support for SUBSCRIBE and NOTIFY............. 16 4.3.1. Detecting support for SUBSCRIBE and NOTIFY............. 17
4.3.2. CANCEL requests........................................ 16 4.3.2. CANCEL requests........................................ 17
4.3.3. Forking................................................ 16 4.3.3. Forking................................................ 17
4.3.4. Dialog creation and termination........................ 17 4.3.4. Dialog creation and termination........................ 17
4.3.5. State Agents and Notifier Migration.................... 18 4.3.5. State Agents and Notifier Migration.................... 19
4.3.6. Polling Resource State................................. 18 4.3.6. Polling Resource State................................. 19
4.3.7. Allow-Events header usage.............................. 19 4.3.7. Allow-Events header usage.............................. 20
4.3.8. PINT Compatibility..................................... 19 4.3.8. PINT Compatibility..................................... 20
5. Event Packages......................................... 19 5. Event Packages......................................... 20
5.1. Appropriateness of Usage............................... 19 5.1. Appropriateness of Usage............................... 20
5.2. Event Template-packages................................ 20 5.2. Event Template-packages................................ 21
5.3. Amount of State to be Conveyed......................... 20 5.3. Amount of State to be Conveyed......................... 21
5.3.1. Complete State Information............................. 21 5.3.1. Complete State Information............................. 22
5.3.2. State Deltas........................................... 21 5.3.2. State Deltas........................................... 22
5.4. Event Package Responsibilities......................... 22 5.4. Event Package Responsibilities......................... 22
5.4.1. Event Package Name..................................... 22 5.4.1. Event Package Name..................................... 23
5.4.2. Event Package Parameters............................... 22 5.4.2. Event Package Parameters............................... 23
5.4.3. SUBSCRIBE Bodies....................................... 22 5.4.3. SUBSCRIBE Bodies....................................... 23
5.4.4. Subscription Duration.................................. 22 5.4.4. Subscription Duration.................................. 23
5.4.5. NOTIFY Bodies.......................................... 23 5.4.5. NOTIFY Bodies.......................................... 24
5.4.6. Notifier processing of SUBSCRIBE requests.............. 23 5.4.6. Notifier processing of SUBSCRIBE requests.............. 24
5.4.7. Notifier generation of NOTIFY requests................. 23 5.4.7. Notifier generation of NOTIFY requests................. 24
5.4.8. Subscriber processing of NOTIFY requests............... 23 5.4.8. Subscriber processing of NOTIFY requests............... 24
5.4.9. Handling of forked requests............................ 23 5.4.9. Handling of forked requests............................ 24
5.4.10. Rate of notifications.................................. 24 5.4.10. Rate of notifications.................................. 25
5.4.11. State Agents........................................... 24 5.4.11. State Agents........................................... 25
5.4.12. Examples............................................... 25 5.4.12. Examples............................................... 26
5.4.13. URI List handling...................................... 25 5.4.13. URI List handling...................................... 26
6. Security Considerations................................ 25 6. Security Considerations................................ 26
6.1. Access Control......................................... 25 6.1. Access Control......................................... 26
6.2. Release of Sensitive Policy Information................ 25 6.2. Release of Sensitive Policy Information................ 26
6.3. Denial-of-Service attacks.............................. 26 6.3. Denial-of-Service attacks.............................. 27
6.4. Replay Attacks......................................... 26 6.4. Replay Attacks......................................... 27
6.5. Man-in-the middle attacks.............................. 26 6.5. Man-in-the middle attacks.............................. 27
6.6. Confidentiality........................................ 27 6.6. Confidentiality........................................ 28
7. IANA Considerations.................................... 27 7. IANA Considerations.................................... 28
7.1. Registration Information............................... 28 7.1. Registration Information............................... 29
7.2. Registration Template.................................. 28 7.2. Registration Template.................................. 29
7.3. Syntax................................................. 29 7.3. Syntax................................................. 30
7.4. New Methods............................................ 29 7.4. New Methods............................................ 30
7.4.1. SUBSCRIBE method....................................... 31 7.4.1. SUBSCRIBE method....................................... 32
7.4.2. NOTIFY method.......................................... 31 7.4.2. NOTIFY method.......................................... 32
7.5. New Headers............................................ 31 7.5. New Headers............................................ 32
7.5.1. "Event" header......................................... 31 7.5.1. "Event" header......................................... 32
7.5.2. "Allow-Events" Header.................................. 32 7.5.2. "Allow-Events" Header.................................. 33
7.5.3. "Subscription-State" Header............................ 32 7.5.3. "Subscription-State" Header............................ 33
7.6. New Response Codes..................................... 33 7.6. New Response Codes..................................... 33
7.6.1. "202 Accepted" Response Code........................... 33 7.6.1. "202 Accepted" Response Code........................... 33
7.6.2. "489 Bad Event" Response Code.......................... 33 7.6.2. "489 Bad Event" Response Code.......................... 33
8. Changes................................................ 33 7.7. Augmented BNF Definitions.............................. 33
8.1. Changes from draft-ietf-...-01......................... 33 8. Changes................................................ 34
8.2. Changes from draft-ietf-...-00......................... 35 8.1. Changes from draft-ietf-...-02......................... 34
8.3. Changes from draft-roach-...-03........................ 36 8.2. Changes from draft-ietf-...-01......................... 35
8.4. Changes from draft-roach-...-02........................ 38 8.3. Changes from draft-ietf-...-00......................... 37
8.5. Changes from draft-roach-...-01........................ 39 9. References............................................. 38
9. References............................................. 40 10. Acknowledgements....................................... 39
10. Acknowledgements....................................... 41 11. Author's Address....................................... 39
11. Author's Address....................................... 41
2. Introduction 2. Introduction
The ability to request asynchronous notification of events proves The ability to request asynchronous notification of events proves
useful in many types of services for which cooperation between useful in many types of services for which cooperation between
end-nodes is required. Examples of such services include end-nodes is required. Examples of such services include
automatic callback services (based on terminal state events), automatic callback services (based on terminal state events),
buddy lists (based on user presence events), message waiting buddy lists (based on user presence events), message waiting
indications (based on mailbox state change events), and PINT indications (based on mailbox state change events), and PINT
status (based on call state events). status (based on call state events).
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complex for a single protocol. Our goal is to provide a complex for a single protocol. Our goal is to provide a
SIP-specific framework for event notification which is not so SIP-specific framework for event notification which is not so
complex as to be unusable for simple features, but which is still complex as to be unusable for simple features, but which is still
flexible enough to provide powerful services. Note, however, that flexible enough to provide powerful services. Note, however, that
event packages based on this framework may define arbitrarily event packages based on this framework may define arbitrarily
complex rules which govern the subscription and notification for complex rules which govern the subscription and notification for
the events or classes of events they describe. the events or classes of events they describe.
This draft does not describe an extension which may be used This draft does not describe an extension which may be used
directly; it must be extended by other drafts (herein referred to directly; it must be extended by other drafts (herein referred to
as "event packages.") In object-oriented design terminology, it as "event packages".) In object-oriented design terminology, it
may be thought of as an abstract base class which must be derived may be thought of as an abstract base class which must be derived
into an instantiatable class by further extensions. Guidelines into an instantiatable class by further extensions. Guidelines
for creating these extensions are described in section 5. for creating these extensions are described in section 5.
2.1. Overview of Operation 2.1. Overview of Operation
The general concept is that entities in the network can subscribe The general concept is that entities in the network can subscribe
to resource or call state for various resources or calls in the to resource or call state for various resources or calls in the
network, and those entities (or entities acting on their behalf) network, and those entities (or entities acting on their behalf)
can send notifications when those states change. can send notifications when those states change.
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|-----SUBSCRIBE---->| Request state subscription |-----SUBSCRIBE---->| Request state subscription
|<-------200--------| Acknowledge subscription |<-------200--------| Acknowledge subscription
|<------NOTIFY----- | Return current state information |<------NOTIFY----- | Return current state information
|--------200------->| |--------200------->|
|<------NOTIFY----- | Return current state information |<------NOTIFY----- | Return current state information
|--------200------->| |--------200------->|
Subscriptions are expired and must be refreshed by subsequent Subscriptions are expired and must be refreshed by subsequent
SUBSCRIBE messages. SUBSCRIBE messages.
2.2. Documentation Conventions
There are several paragraphs throughout the document which
provide motivational or clarifying text. Such passages are
non-normative, and are provided only to assist with reader
comprehension. These passages are set off from the remainder of
the text by being indented thus:
This is an example of non-normative explanatory text. It does
not form part of the specification, and is used only for
clarification.
Numbers in square brackets (e.g. [1]) denote a reference to one
of the entries in the References section; see section 9.
The all-capital terms "MUST", "SHOULD", "MAY", "SHOULD NOT", and
"MUST NOT" are used as defined in RFC 2119 [8].
The use of quotation marks next to periods and commas follows the
convention used by the American Mathematical Society; although
contrary to traditional American English convention, this usage
lends clarity to certain passages.
3. Definitions 3. Definitions
Event Package: An event package is an additional specification Event Package: An event package is an additional specification
which defines a set of state information to be reported by a which defines a set of state information to be reported by a
notifier to a subscriber. Event packages also define further notifier to a subscriber. Event packages also define further
syntax and semantics based on the framework defined by this syntax and semantics based on the framework defined by this
document required to convey such state information. document required to convey such state information.
Event Template-Package: An event template-package is a special Event Template-Package: An event template-package is a special
kind of event package which defines a set of state which may kind of event package which defines a set of state which may
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NOTIFY message to a subscriber to inform the subscriber of NOTIFY message to a subscriber to inform the subscriber of
the state of a resource. the state of a resource.
Notifier: A notifier is a user agent which generates NOTIFY Notifier: A notifier is a user agent which generates NOTIFY
requests for the purpose of notifying subscribers of the requests for the purpose of notifying subscribers of the
state of a resource. Notifiers typically also accept state of a resource. Notifiers typically also accept
SUBSCRIBE requests to create subscriptions. SUBSCRIBE requests to create subscriptions.
State Agent: A state agent is a notifier which publishes state State Agent: A state agent is a notifier which publishes state
information on behalf of a resource; in order to do so, it information on behalf of a resource; in order to do so, it
may need gather such state information from multiple sources. may need to gather such state information from multiple
State Agents always have complete state information for the sources. State agents always have complete state information
resource for which it is creating notifications. for the resource for which it is creating notifications.
Subscriber: A subscriber is a user agent which receives NOTIFY Subscriber: A subscriber is a user agent which receives NOTIFY
requests from notifiers; these NOTIFY requests contain requests from notifiers; these NOTIFY requests contain
information about the state of a resource in which the information about the state of a resource in which the
subscriber is interested. Subscribers typically also generate subscriber is interested. Subscribers typically also generate
SUBSCRIBE requests and send them to notifiers to create SUBSCRIBE requests and send them to notifiers to create
subscriptions. subscriptions.
Subscription: A subscription is a set of application state Subscription: A subscription is a set of application state
associated with a dialog. This application state includes a associated with a dialog. This application state includes a
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Subscription Migration: Subscription migration is the act of Subscription Migration: Subscription migration is the act of
moving a subscription from one notifier to another notifier. moving a subscription from one notifier to another notifier.
4. Node Behavior 4. Node Behavior
4.1. Description of SUBSCRIBE Behavior 4.1. Description of SUBSCRIBE Behavior
The SUBSCRIBE method is used to request current state and state The SUBSCRIBE method is used to request current state and state
updates from a remote node. updates from a remote node.
4.1.1. Subscription duration 4.1.1. Subscription Duration
SUBSCRIBE requests SHOULD contain an "Expires" header (defined in SUBSCRIBE requests SHOULD contain an "Expires" header (defined in
SIP [1] ). This expires value indicates the duration of the SIP [1] ). This expires value indicates the duration of the
subscription. In order to keep subscriptions effective beyond the subscription. In order to keep subscriptions effective beyond the
duration communicated in the "Expires" header, subscribers need duration communicated in the "Expires" header, subscribers need
to refresh subscriptions on a periodic basis using a new to refresh subscriptions on a periodic basis using a new
SUBSCRIBE message on the same dialog as defined in SIP [1] . SUBSCRIBE message on the same dialog as defined in SIP [1] .
If no "Expires" header is present in a SUBSCRIBE request, the If no "Expires" header is present in a SUBSCRIBE request, the
implied default is defined by the event package being used. implied default is defined by the event package being used.
200-class responses to SUBSCRIBE requests also MUST contain an 200-class responses to SUBSCRIBE requests also MUST contain an
"Expires" header. The period of time in the response MAY be "Expires" header. The period of time in the response MAY be
shorter or longer than specified in the request. The period of shorter but MUST NOT be longer than specified in the request. The
time in the response is the one which defines the duration of the period of time in the response is the one which defines the
subscription. duration of the subscription.
An "expires" parameter on the "Contact" header has no semantics An "expires" parameter on the "Contact" header has no semantics
for SUBSCRIBE and is explicitly not equivalent to an "Expires" for SUBSCRIBE and is explicitly not equivalent to an "Expires"
header in a SUBSCRIBE request or response. header in a SUBSCRIBE request or response.
A natural consequence of this scheme is that a SUBSCRIBE with an A natural consequence of this scheme is that a SUBSCRIBE with an
"Expires" of 0 constitutes a request to unsubscribe from an "Expires" of 0 constitutes a request to unsubscribe from an
event. event.
In addition to being a request to unsubscribe, a SUBSCRIBE
message with "Expires" of 0 also causes a fetch of state; see
section 4.3.6.
Notifiers may also wish to cancel subscriptions to events; this Notifiers may also wish to cancel subscriptions to events; this
is useful, for example, when the resource to which a subscription is useful, for example, when the resource to which a subscription
refers is no longer available. Further details on this mechanism refers is no longer available. Further details on this mechanism
are discussed in section 4.2.2. are discussed in section 4.2.2.
4.1.2. Identification of Subscribed Events and Event Classes 4.1.2. Identification of Subscribed Events and Event Classes
Identification of events is provided by three pieces of Identification of events is provided by three pieces of
information: Request URI, Event Type, and (optionally) message information: Request URI, Event Type, and (optionally) message
body. body.
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resource. A 202 response merely indicates that the subscription resource. A 202 response merely indicates that the subscription
has been understood, and that authorization may or may not have has been understood, and that authorization may or may not have
been granted. been granted.
The "Expires" header in a 200-class response to SUBSCRIBE The "Expires" header in a 200-class response to SUBSCRIBE
indicates the actual duration for which the subscription will indicates the actual duration for which the subscription will
remain active (unless refreshed). remain active (unless refreshed).
Non-200 class final responses indicate that no subscription or Non-200 class final responses indicate that no subscription or
dialog has been created, and no subsequent NOTIFY message will be dialog has been created, and no subsequent NOTIFY message will be
sent. All non-200 class responses (with the exception of "489," sent. All non-200 class responses (with the exception of "489",
described herein) have the same meanings and handling as described herein) have the same meanings and handling as
described in SIP [1] . described in SIP [1] .
A SUBSCRIBE request MAY include an "id" parameter in its "Event" A SUBSCRIBE request MAY include an "id" parameter in its "Event"
header to allow differentiation between multiple subscriptions in header to allow differentiation between multiple subscriptions in
the same dialog. the same dialog.
4.1.4.2. Refreshing of Subscriptions 4.1.4.2. Refreshing of Subscriptions
At any time before a subscription expires, the subscriber may At any time before a subscription expires, the subscriber may
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If a SUBSCRIBE request to refresh a subscription fails with a If a SUBSCRIBE request to refresh a subscription fails with a
non-481 response, the original subscription is still considered non-481 response, the original subscription is still considered
valid for the duration of the most recently known "Expires" value valid for the duration of the most recently known "Expires" value
as negotiated by SUBSCRIBE and its response, or as communicated as negotiated by SUBSCRIBE and its response, or as communicated
by NOTIFY in the "Subscription-State" header "expires" parameter. by NOTIFY in the "Subscription-State" header "expires" parameter.
4.1.4.3. Unsubscribing 4.1.4.3. Unsubscribing
Unsubscribing is handled in the same way as refreshing of a Unsubscribing is handled in the same way as refreshing of a
subscription, with the "Expires" header set to "0." Note that a subscription, with the "Expires" header set to "0". Note that a
successful unsubscription will also trigger a final "NOTIFY". successful unsubscription will also trigger a final NOTIFY
message.
4.1.4.4. Confirmation of Subscription Creation 4.1.4.4. Confirmation of Subscription Creation
The subscriber can expect to receive a NOTIFY message from each The subscriber can expect to receive a NOTIFY message from each
node which has processed a successful subscription or node which has processed a successful subscription or
subscription refresh. Until the first NOTIFY message arrives, the subscription refresh. Until the first NOTIFY message arrives, the
subscriber should consider the state of the subscribed resource subscriber should consider the state of the subscribed resource
to be in a neutral state. Event packages which define new event to be in a neutral state. Event packages which define new event
packages MUST define this "neutral state" in such a way that packages MUST define this "neutral state" in such a way that
makes sense for their application (see section 5.4.7. ). makes sense for their application (see section 5.4.7. ).
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the SUBSCRIBE transaction has completed. the SUBSCRIBE transaction has completed.
Except as noted above, processing of this NOTIFY is the same as Except as noted above, processing of this NOTIFY is the same as
in section 4.2.4. in section 4.2.4.
4.1.5. Proxy SUBSCRIBE Behavior 4.1.5. Proxy SUBSCRIBE Behavior
Proxies need no additional behavior beyond that described in SIP Proxies need no additional behavior beyond that described in SIP
[1] to support SUBSCRIBE. If a proxy wishes to see all of the [1] to support SUBSCRIBE. If a proxy wishes to see all of the
SUBSCRIBE and NOTIFY requests for a given dialog, it MUST SUBSCRIBE and NOTIFY requests for a given dialog, it MUST
record-route all SUBSCRIBE and NOTIFY requests. record-route the initial SUBSCRIBE and any dialog-establishing
NOTIFY requests. Such proxies SHOULD also record-route all other
SUBSCRIBE and NOTIFY requests.
4.1.6. Notifier SUBSCRIBE Behavior 4.1.6. Notifier SUBSCRIBE Behavior
4.1.6.1. Initial SUBSCRIBE Transaction Processing 4.1.6.1. Initial SUBSCRIBE Transaction Processing
In no case should a SUBSCRIBE transaction extend for any longer In no case should a SUBSCRIBE transaction extend for any longer
than the time necessary for automated processing. In particular, than the time necessary for automated processing. In particular,
notifiers MUST NOT wait for a user response before returning a notifiers MUST NOT wait for a user response before returning a
final response to a SUBSCRIBE request. final response to a SUBSCRIBE request.
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with a user would often exceed 64*T1 seconds. with a user would often exceed 64*T1 seconds.
The notifier SHOULD check that the event package specified in the The notifier SHOULD check that the event package specified in the
"Event" header is understood. If not, the notifier SHOULD return "Event" header is understood. If not, the notifier SHOULD return
a "489 Bad Event" response to indicate that the specified a "489 Bad Event" response to indicate that the specified
event/event class is not understood. event/event class is not understood.
The notifier SHOULD also perform any necessary authentication and The notifier SHOULD also perform any necessary authentication and
authorization per its local policy. See section 4.1.6.3. authorization per its local policy. See section 4.1.6.3.
If the notifier has local policy specifying a minimum allowed
duration for subscriptions, it SHOULD verify that the "Expires"
header in the SUBSCRIBE request is not smaller than such a
duration. If not, the notifier SHOULD return a "423 Interval too
small" error which contains a "Min-Expires" header field. The
"Min-Expires" header field is describe in SIP [1].
If the notifier is able to immediately determine that it If the notifier is able to immediately determine that it
understands the event package, that the authenticated subscriber understands the event package, that the authenticated subscriber
is authorized to subscribe, and that there are no other barriers is authorized to subscribe, and that there are no other barriers
to creating the subscription, it creates the subscription and a to creating the subscription, it creates the subscription and a
dialog (if necessary), and returns a "200 OK" response (unless dialog (if necessary), and returns a "200 OK" response (unless
doing so would reveal authorization policy in an undesirable doing so would reveal authorization policy in an undesirable
fashion; see section 6.2. ). fashion; see section 6.2. ).
If the notifier cannot immediately create the subscription (e.g. If the notifier cannot immediately create the subscription (e.g.
it needs to wait for user input for authorization, or is acting it needs to wait for user input for authorization, or is acting
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If the notifier owner is interactively queried to determine If the notifier owner is interactively queried to determine
whether a subscription is allowed, a "202 Accept" response is whether a subscription is allowed, a "202 Accept" response is
returned immediately. Note that a NOTIFY message is still formed returned immediately. Note that a NOTIFY message is still formed
and sent under these circumstances, as described in the previous and sent under these circumstances, as described in the previous
section. section.
If subscription authorization was delayed and the notifier wishes If subscription authorization was delayed and the notifier wishes
to convey that such authorization has been declined, it may do so to convey that such authorization has been declined, it may do so
by sending a NOTIFY message containing a "Subscription-State" by sending a NOTIFY message containing a "Subscription-State"
header with a value of "terminated" and a reason parameter of header with a value of "terminated" and a reason parameter of
"rejected." "rejected".
4.1.6.4. Refreshing of Subscriptions 4.1.6.4. Refreshing of Subscriptions
When a notifier receives a subscription refresh, assuming that When a notifier receives a subscription refresh, assuming that
the subscriber is still authorized, the notifier updates the the subscriber is still authorized, the notifier updates the
expiration time for subscription. As with the initial expiration time for subscription. As with the initial
subscription, the server MAY shorten the amount of time until subscription, the server MAY shorten the amount of time until
expiration, but MUST NOT increase it. The final expiration time expiration, but MUST NOT increase it. The final expiration time
is placed in the "Expires" header in the response. If the is placed in the "Expires" header in the response. If the
duration specified in a SUBSCRIBE message is unacceptably short, duration specified in a SUBSCRIBE message is unacceptably short,
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Subscription does not exist" response (unless some other 400- or Subscription does not exist" response (unless some other 400- or
500-class error code is more applicable), as described in section 500-class error code is more applicable), as described in section
4.2.4. In other words, knowledge of a subscription must exist in 4.2.4. In other words, knowledge of a subscription must exist in
both the subscriber and the notifier to be valid, even if both the subscriber and the notifier to be valid, even if
installed via a non-SUBSCRIBE mechanism. installed via a non-SUBSCRIBE mechanism.
A NOTIFY does not terminate its corresponding subscription; in A NOTIFY does not terminate its corresponding subscription; in
other words, a single SUBSCRIBE request may trigger several other words, a single SUBSCRIBE request may trigger several
NOTIFY requests. NOTIFY requests.
4.2.1. Identification of reported events, event classes, and current 4.2.1. Identification of Reported Events, Event Classes, and Current
state State
Identification of events being reported in a notification is very Identification of events being reported in a notification is very
similar to that described for subscription to events (see section similar to that described for subscription to events (see section
4.1.2. ). 4.1.2. ).
As in SUBSCRIBE requests, NOTIFY "Event" headers will contain a As in SUBSCRIBE requests, NOTIFY "Event" headers will contain a
single event package name for which a notification is being single event package name for which a notification is being
generated. The package name in the "Event" header MUST match the generated. The package name in the "Event" header MUST match the
"Event" header in the corresponding SUBSCRIBE message. If an "id" "Event" header in the corresponding SUBSCRIBE message. If an "id"
parameter was present in the SUBSCRIBE message, that "id" parameter was present in the SUBSCRIBE message, that "id"
parameter MUST also be present in the corresponding NOTIFY parameter MUST also be present in the corresponding NOTIFY
messages. messages.
If the event package to which the event package name corresponds Event packages may define semantics associated with the body of
defines behavior associated with the body of its NOTIFY requests, their NOTIFY requests; if they do so, those semantics apply.
those semantics apply. This information is expected to provide NOTIFY bodies are expected to provide additional details about
additional details about the nature of the event which has the nature of the event which has occurred and the resultant
occurred and the resultant resource state. resource state.
When present, the body of the NOTIFY request MUST be formatted When present, the body of the NOTIFY request MUST be formatted
into one of the body formats specified in the "Accept" header of into one of the body formats specified in the "Accept" header of
the corresponding SUBSCRIBE request. This body will contain the corresponding SUBSCRIBE request. This body will contain
either the state of the subscribed resource or a pointer to such either the state of the subscribed resource or a pointer to such
state in the form of a URI. state in the form of a URI.
4.2.2. Notifier NOTIFY Behavior 4.2.2. Notifier NOTIFY Behavior
When a SUBSCRIBE request is answered with a 200-class response, When a SUBSCRIBE request is answered with a 200-class response,
the notifier MUST immediately construct and send a NOTIFY request the notifier MUST immediately construct and send a NOTIFY request
to the subscriber. When a change in the subscribed state occurs, to the subscriber. When a change in the subscribed state occurs,
the notifier SHOULD immediately construct and send a NOTIFY the notifier SHOULD immediately construct and send a NOTIFY
request, subject to authorization, local policy, and throttling request, subject to authorization, local policy, and throttling
considerations. considerations.
A NOTIFY request is considered failed if the response times out, A NOTIFY request is considered failed if the response times out,
or a non-200 class response code is received which has no or a non-200 class response code is received which has no
"Retry-After" header and no implied further action which can be "Retry-After" header and no implied further action which can be
taken to retry the request (e.g. "401 Authorization Required.") taken to retry the request (e.g. "401 Authorization Required".)
If the NOTIFY request fails (as defined above) due to a timeout If the NOTIFY request fails (as defined above) due to a timeout
condition, and the subscription was installed using a soft-state condition, and the subscription was installed using a soft-state
mechanism (such as SUBSCRIBE), the notifier SHOULD remove the mechanism (such as SUBSCRIBE), the notifier SHOULD remove the
subscription. subscription.
This behavior prevents unnecessary transmission of state This behavior prevents unnecessary transmission of state
information for subscribers who have crashed or disappeared information for subscribers who have crashed or disappeared
from the network. Because such transmissions will be sent 11 from the network. Because such transmissions will be sent 11
times (instead of the typical single transmission for times (instead of the typical single transmission for
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receiving a notify for an unknown subscription would need to receiving a notify for an unknown subscription would need to
send an error status code in response to the NOTIFY and also send an error status code in response to the NOTIFY and also
send a SUBSCRIBE request to remove the subscription. Since send a SUBSCRIBE request to remove the subscription. Since
this behavior would make subscribers available for use as this behavior would make subscribers available for use as
amplifiers in denial of service attacks, we have instead amplifiers in denial of service attacks, we have instead
elected to give the 481 response special meaning: it is used elected to give the 481 response special meaning: it is used
to indicate that a subscription must be cancelled under all to indicate that a subscription must be cancelled under all
circumstances. circumstances.
NOTIFY requests MUST contain a "Subscription-State" header with a NOTIFY requests MUST contain a "Subscription-State" header with a
value of "active," "pending," or "terminated." The "active" value value of "active", "pending", or "terminated". The "active" value
indicates that the subscription has been accepted and has been indicates that the subscription has been accepted and has been
authorized (in most cases; see section 6.2. ). The "pending" authorized (in most cases; see section 6.2. ). The "pending"
value indicates that the subscription has been received, but that value indicates that the subscription has been received, but that
policy information is insufficient to accept or deny the policy information is insufficient to accept or deny the
subscription at this time. The "terminated" value indicates that subscription at this time. The "terminated" value indicates that
the subscription is not active. the subscription is not active.
If the value of the "Subscription-State" header is "active" or If the value of the "Subscription-State" header is "active" or
"pending," the notifier SHOULD also include in the "pending", the notifier SHOULD also include in the
"Subscription-State" header an "expires" parameter which "Subscription-State" header an "expires" parameter which
indicates the time remaining on the subscription. The notifier indicates the time remaining on the subscription. The notifier
MAY use this mechanism to shorten a subscription; however, this MAY use this mechanism to shorten a subscription; however, this
mechanism MUST NOT be used to lengthen a subscription. mechanism MUST NOT be used to lengthen a subscription.
Including expiration information for active and pending Including expiration information for active and pending
subscriptions is useful in case the SUBSCRIBE request forks, subscriptions is useful in case the SUBSCRIBE request forks,
since the response to a forked SUBSCRIBE may not be received since the response to a forked SUBSCRIBE may not be received
by the subscriber. Note well that this "expires" value is a by the subscriber. Note well that this "expires" value is a
parameter on the "Subscription-State" header, NOT an parameter on the "Subscription-State" header, NOT an
"Expires" header. "Expires" header.
If the value of the "Subscription-State" header is "terminated," If the value of the "Subscription-State" header is "terminated",
the notifier SHOULD also include a "reason" parameter. The the notifier SHOULD also include a "reason" parameter. The
notifier MAY also include a "retry-after" parameter, where notifier MAY also include a "retry-after" parameter, where
appropriate. For details on the value and semantics of the appropriate. For details on the value and semantics of the
"reason" and "retry-after" parameters, see section 4.2.4. "reason" and "retry-after" parameters, see section 4.2.4.
4.2.3. Proxy NOTIFY Behavior 4.2.3. Proxy NOTIFY Behavior
Proxies need no additional behavior beyond that described in SIP Proxies need no additional behavior beyond that described in SIP
[1] to support NOTIFY. If a proxy wishes to see all of the [1] to support NOTIFY. If a proxy wishes to see all of the
SUBSCRIBE and NOTIFY requests for a given dialog, it MUST SUBSCRIBE and NOTIFY requests for a given dialog, it MUST
record-route all SUBSCRIBE and NOTIFY requests. record-route the initial SUBSCRIBE and any dialog-establishing
NOTIFY requests. Such proxies SHOULD also record-route all other
SUBSCRIBE and NOTIFY requests.
4.2.4. Subscriber NOTIFY Behavior 4.2.4. Subscriber NOTIFY Behavior
Upon receiving a NOTIFY request, the subscriber should check that Upon receiving a NOTIFY request, the subscriber should check that
it matches at least one of its outstanding subscriptions; if not, it matches at least one of its outstanding subscriptions; if not,
it MUST return a "481 Subscription does not exist" response it MUST return a "481 Subscription does not exist" response
unless another 400- or 500-class response is more appropriate. unless another 400- or 500-class response is more appropriate.
The rules for matching NOTIFY requests with subscriptions that The rules for matching NOTIFY requests with subscriptions that
create a new dialog is described in section 4.3.4. Notifications create a new dialog are described in section 4.3.4. Notifications
for subscriptions which were created inside an existing dialog for subscriptions which were created inside an existing dialog
match if they are in the same dialog and the "Event" headers match if they are in the same dialog and the "Event" headers
match (as described in section 7.5.1. ) match (as described in section 7.5.1. )
If, for some reason, the event package designated in the "Event" If, for some reason, the event package designated in the "Event"
header of the NOTIFY request is not supported, the subscriber header of the NOTIFY request is not supported, the subscriber
will respond with a "489 Bad Event" response. will respond with a "489 Bad Event" response.
To prevent spoofing of events, NOTIFY requests SHOULD be To prevent spoofing of events, NOTIFY requests SHOULD be
authenticated, using any defined SIP authentication mechanism. authenticated, using any defined SIP authentication mechanism.
NOTIFY requests MUST contain "Subscription-State" headers which NOTIFY requests MUST contain "Subscription-State" headers which
indicate the status of the subscription. indicate the status of the subscription.
If the "Subscription-State" header value is "active," it means If the "Subscription-State" header value is "active", it means
that the subscription has been accepted and (in general) has been that the subscription has been accepted and (in general) has been
authorized. If the header also contains an "expires" parameter, authorized. If the header also contains an "expires" parameter,
the subscriber SHOULD take it as the authoritative subscription the subscriber SHOULD take it as the authoritative subscription
duration and adjust accordingly. The "retry-after" and "reason" duration and adjust accordingly. The "retry-after" and "reason"
parameters have no semantics for "active." parameters have no semantics for "active".
If the "Subscription-State" value is "pending," the subscription If the "Subscription-State" value is "pending", the subscription
has been received by the notifier, but there is insufficient has been received by the notifier, but there is insufficient
policy information to grant or deny the subscription yet. If the policy information to grant or deny the subscription yet. If the
header also contains an "expires" parameter, the subscriber header also contains an "expires" parameter, the subscriber
SHOULD take it as the authoritative subscription duration and SHOULD take it as the authoritative subscription duration and
adjust accordingly. No further action is necessary on the part of adjust accordingly. No further action is necessary on the part of
the subscriber. The "retry-after" and "reason" parameters have no the subscriber. The "retry-after" and "reason" parameters have no
semantics for "pending." semantics for "pending".
If the "Subscription-State" value is "terminated," the subscriber If the "Subscription-State" value is "terminated", the subscriber
should consider the subscription terminated. The "expires" should consider the subscription terminated. The "expires"
parameter has no semantics for "terminated." If a reason code is parameter has no semantics for "terminated". If a reason code is
present, the client should behave as described below. If no present, the client should behave as described below. If no
reason code or an unknown reason code is present, the client MAY reason code or an unknown reason code is present, the client MAY
attempt to re-subscribe at any time (unless a "retry-after" attempt to re-subscribe at any time (unless a "retry-after"
parameter is present, in which case the client SHOULD NOT attempt parameter is present, in which case the client SHOULD NOT attempt
re-subscription until after the number of seconds specified by re-subscription until after the number of seconds specified by
the "retry-after" parameter). The defined reason codes are: the "retry-after" parameter). The defined reason codes are:
deactivated: The subscription has been terminated, but the client deactivated: The subscription has been terminated, but the client
SHOULD retry immediately with a new subscription. One primary SHOULD retry immediately with a new subscription. One primary
use of such a status code is to allow migration of use of such a status code is to allow migration of
subscriptions between nodes. The "retry-after" parameter has subscriptions between nodes. The "retry-after" parameter has
no semantics for "deactivated." no semantics for "deactivated".
probation: The subscription has been terminated, but the client probation: The subscription has been terminated, but the client
SHOULD retry at some later time. If a "retry-after" parameter SHOULD retry at some later time. If a "retry-after" parameter
is also present, the client SHOULD wait at least the number is also present, the client SHOULD wait at least the number
of seconds specified by that parameter before attempting to of seconds specified by that parameter before attempting to
re-subscribe. re-subscribe.
rejected: The subscription has been terminated due to change in rejected: The subscription has been terminated due to change in
authorization policy. Clients SHOULD NOT attempt to authorization policy. Clients SHOULD NOT attempt to
re-subscribe. The "retry-after" parameter has no semantics re-subscribe. The "retry-after" parameter has no semantics
for "rejected." for "rejected".
timeout: The subscription has been terminated because it was not timeout: The subscription has been terminated because it was not
refreshed before it expired. Clients MAY re-subscribe refreshed before it expired. Clients MAY re-subscribe
immediately. The "retry-after" parameter has no semantics for immediately. The "retry-after" parameter has no semantics for
"timeout." "timeout".
giveup: The subscription has been terminated because the notifier giveup: The subscription has been terminated because the notifier
could not obtain authorization in a timely fashion. If a could not obtain authorization in a timely fashion. If a
"retry-after" parameter is also present, the client SHOULD "retry-after" parameter is also present, the client SHOULD
wait at least the number of seconds specified by that wait at least the number of seconds specified by that
parameter before attempting to re-subscribe; otherwise, the parameter before attempting to re-subscribe; otherwise, the
client MAY retry immediately, but will likely get put back client MAY retry immediately, but will likely get put back
into pending state. into pending state.
Once the notification is deemed acceptable to the subscriber, the Once the notification is deemed acceptable to the subscriber, the
subscriber SHOULD return a 200 response. In general, it is not subscriber SHOULD return a 200 response. In general, it is not
expected that NOTIFY responses will contain bodies; however, they expected that NOTIFY responses will contain bodies; however, they
MAY, if the NOTIFY request contained an "Accept" header. MAY, if the NOTIFY request contained an "Accept" header.
Other responses defined in SIP [1] may also be returned, as Other responses defined in SIP [1] may also be returned, as
appropriate. appropriate. In no case should a NOTIFY transaction extend for
any longer than the time necessary for automated processing. In
particular, subscribers MUST NOT wait for a user response before
returning a final response to a NOTIFY request.
4.3. General 4.3. General
4.3.1. Detecting support for SUBSCRIBE and NOTIFY 4.3.1. Detecting support for SUBSCRIBE and NOTIFY
Neither SUBSCRIBE nor NOTIFY necessitate the use of "Require" or Neither SUBSCRIBE nor NOTIFY necessitate the use of "Require" or
"Proxy-Require" headers; similarly, there is no token defined for "Proxy-Require" headers; similarly, there is no token defined for
"Supported" headers. If necessary, clients may probe for the "Supported" headers. If necessary, clients may probe for the
support of SUBSCRIBE and NOTIFY using the OPTIONS request defined support of SUBSCRIBE and NOTIFY using the OPTIONS request defined
in SIP [1] . in SIP [1] .
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specifically announce support for SUBSCRIBE and NOTIFY messages specifically announce support for SUBSCRIBE and NOTIFY messages
when registering. (See reference [7] for details on the "methods" when registering. (See reference [7] for details on the "methods"
parameter). parameter).
4.3.2. CANCEL requests 4.3.2. CANCEL requests
No semantics are associated with cancelling SUBSCRIBE or NOTIFY. No semantics are associated with cancelling SUBSCRIBE or NOTIFY.
4.3.3. Forking 4.3.3. Forking
Successful SUBSCRIBE requests will receive only one 200-class In accordance with the rules for proxying non-INVITE requests as
response; however, due to forking, the subscription may have been defined in SIP [1], successful SUBSCRIBE requests will receive
accepted by multiple nodes. The subscriber MUST therefore be only one 200-class response; however, due to forking, the
prepared to receive NOTIFY requests with "From:" tags which subscription may have been accepted by multiple nodes. The
differ from the "To:" tag received in the SUBSCRIBE 200-class subscriber MUST therefore be prepared to receive NOTIFY requests
response. with "From:" tags which differ from the "To:" tag received in the
SUBSCRIBE 200-class response.
If multiple NOTIFY messages are received in response to a single If multiple NOTIFY messages are received in response to a single
SUBSCRIBE message, they represent different destinations to which SUBSCRIBE message, they represent different destinations to which
the SUBSCRIBE request was forked. For information on subscriber the SUBSCRIBE request was forked. For information on subscriber
handling in such situations, see section 5.4.9. handling in such situations, see section 5.4.9.
4.3.4. Dialog creation and termination 4.3.4. Dialog creation and termination
If an initial SUBSCRIBE request is not sent on an pre-existing If an initial SUBSCRIBE request is not sent on a pre-existing
dialog, the subscriber will wait for a response to the SUBSCRIBE dialog, the subscriber will wait for a response to the SUBSCRIBE
request or a matching NOTIFY. request or a matching NOTIFY.
Responses are matched to such SUBSCRIBE requests if they contain Responses are matched to such SUBSCRIBE requests if they contain
the same the same "Call-ID," the same "From" header field, the the same the same "Call-ID", the same "From" header field, the
same "To" header field, excluding the "tag," and the same "CSeq." same "To" header field, excluding the "tag", and the same "CSeq".
Rules for the comparison of these headers are described in SIP Rules for the comparison of these headers are described in SIP
[1] . If a 200-class response matches such a SUBSCRIBE request, [1] . If a 200-class response matches such a SUBSCRIBE request,
it creates a new subscription and a new dialog (unless they have it creates a new subscription and a new dialog (unless they have
already been created by a matching NOTIFY request; see below). already been created by a matching NOTIFY request; see below).
NOTIFY requests are matched to such SUBSCRIBE requests if they NOTIFY requests are matched to such SUBSCRIBE requests if they
contain the same "Call-ID," a "From" header field which matches contain the same "Call-ID", a "From" header field which matches
the "To" header field of the SUBSCRIBE, excluding the "tag," a the "To" header field of the SUBSCRIBE, excluding the "tag", a
"To" header field which matches the "From" header field of the "To" header field which matches the "From" header field of the
SUBSCRIBE, and the same "Event" header field. Rules for SUBSCRIBE, and the same "Event" header field. Rules for
comparisons of the "Event" headers are described in section comparisons of the "Event" headers are described in section
7.5.1. If a matching NOTIFY request contains a 7.5.1. If a matching NOTIFY request contains a
"Subscription-State" of "active" or "pending," it creates a new "Subscription-State" of "active" or "pending", it creates a new
subscription and a new dialog (unless the have already been subscription and a new dialog (unless they have already been
created by a matching response, as described above). created by a matching response, as described above).
If an initial SUBSCRIBE is sent on a pre-existing dialog, a If an initial SUBSCRIBE is sent on a pre-existing dialog, a
matching 200-class response or successful NOTIFY request merely matching 200-class response or successful NOTIFY request merely
creates a new subscription associated with that dialog. creates a new subscription associated with that dialog.
Multiple subscriptions can be associated with a single dialog. Multiple subscriptions can be associated with a single dialog.
Subscriptions may also exist in dialogs associated with Subscriptions may also exist in dialogs associated with
INVITE-created application state and other application state INVITE-created application state and other application state
created by mechanisms defined in other specifications. These sets created by mechanisms defined in other specifications. These sets
of application state do not interact beyond the behavior of application state do not interact beyond the behavior
described for a dialog (e.g. route set handling). described for a dialog (e.g. route set handling).
A subscription is destroyed when a notifier sends a NOTIFY A subscription is destroyed when a notifier sends a NOTIFY
request with a "Subscription-State" of "terminated". request with a "Subscription-State" of "terminated".
A subscriber may send a SUBSCRIBE request with an A subscriber may send a SUBSCRIBE request with an "Expires"
"Expiration" header of 0 in order to trigger the sending of header of 0 in order to trigger the sending of such a NOTIFY
such a NOTIFY request; however, for the purposes of request; however, for the purposes of subscription and dialog
subscription and dialog lifetime, the subscription is not lifetime, the subscription is not considered terminated until
considered terminated until the NOTIFY with a the NOTIFY with a "Subscription-State" of "terminated" is
"Subscription-State" of "terminated" is sent. sent.
If a subscription's destruction leaves no other application state If a subscription's destruction leaves no other application state
associated with the dialog, the dialog terminates. The associated with the dialog, the dialog terminates. The
destruction of other application state (such as that created by destruction of other application state (such as that created by
an INVITE) will not terminate the dialog if a subscription is an INVITE) will not terminate the dialog if a subscription is
still associated with that dialog. still associated with that dialog.
Note that the above behavior means that a dialog created with Note that the above behavior means that a dialog created with
an INVITE does not necessarily terminate upon receipt of a an INVITE does not necessarily terminate upon receipt of a
BYE. BYE. Similarly, in the case that several subscriptions are
associated with a single dialog, the dialog does not
terminate until all the subscriptions in it are destroyed.
4.3.5. State Agents and Notifier Migration 4.3.5. State Agents and Notifier Migration
When state agents (see section 5.4.11. ) are used, it is often When state agents (see section 5.4.11. ) are used, it is often
useful to allow migration of subscriptions between state agents useful to allow migration of subscriptions between state agents
and the nodes for which they are providing state aggregation (or and the nodes for which they are providing state aggregation (or
even among various state agents). Such migration may be effected even among various state agents). Such migration may be effected
by sending a "NOTIFY" with an "Subscription-State" header of by sending a NOTIFY message with a "Subscription-State" header of
"terminated," and a reason parameter of "deactivated." This "terminated", and a reason parameter of "deactivated". This
NOTIFY request is otherwise normal, and is formed as described in NOTIFY request is otherwise normal, and is formed as described in
section 4.2.2. section 4.2.2.
Upon receipt of this NOTIFY message, the subscriber SHOULD Upon receipt of this NOTIFY message, the subscriber SHOULD
attempt to re-subscribe (as described in the preceding sections). attempt to re-subscribe (as described in the preceding sections).
Note that this subscription is established on a new dialog, and Note that this subscription is established on a new dialog, and
does not re-use the route set from the previous subscription does not re-use the route set from the previous subscription
dialog. dialog.
The actual migration is effected by making a change to the policy The actual migration is effected by making a change to the policy
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Of course, an immediate fetch while a subscription is active may Of course, an immediate fetch while a subscription is active may
be effected by sending a SUBSCRIBE with an "Expires" equal to the be effected by sending a SUBSCRIBE with an "Expires" equal to the
number of seconds remaining in the subscription. number of seconds remaining in the subscription.
Upon receipt of this SUBSCRIBE request, the notifier (or Upon receipt of this SUBSCRIBE request, the notifier (or
notifiers, if the SUBSCRIBE request was forked) will send a notifiers, if the SUBSCRIBE request was forked) will send a
NOTIFY request containing resource state in the same dialog. NOTIFY request containing resource state in the same dialog.
Note that the NOTIFY messages triggered by SUBSCRIBE messages Note that the NOTIFY messages triggered by SUBSCRIBE messages
with "Expire" headers of 0 will contain a "Subscription-State" with "Expires" headers of 0 will contain a "Subscription-State"
value of "terminated," and a "reason" parameter of "timeout." value of "terminated", and a "reason" parameter of "timeout".
4.3.7. Allow-Events header usage 4.3.7. Allow-Events header usage
The "Allow-Events" header, if present, includes a list of tokens The "Allow-Events" header, if present, includes a list of tokens
which indicates the event packages supported by the client (if which indicates the event packages supported by the client (if
sent in a request) or server (if sent in a response). In other sent in a request) or server (if sent in a response). In other
words, a node sending an "Allow-Events" header is advertising words, a node sending an "Allow-Events" header is advertising
that it can process SUBSCRIBE requests and generate NOTIFY that it can process SUBSCRIBE requests and generate NOTIFY
requests for all of the event packages listed in that header. requests for all of the event packages listed in that header.
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is SIP an appropriate mechanism for the problem set? Is SIP being is SIP an appropriate mechanism for the problem set? Is SIP being
selected because of some unique feature provided by the protocol selected because of some unique feature provided by the protocol
(e.g. user mobility), or merely because "it can be done?" If you (e.g. user mobility), or merely because "it can be done?" If you
find yourself defining event packages for notifications related find yourself defining event packages for notifications related
to, for example, network management or the temperature inside to, for example, network management or the temperature inside
your car's engine, you may want to reconsider your selection of your car's engine, you may want to reconsider your selection of
protocols. protocols.
Those interested in extending the mechanism defined in this Those interested in extending the mechanism defined in this
document are urged to read "Guidelines for Authors of SIP document are urged to read "Guidelines for Authors of SIP
Extensions" [2] for further guidance regarding appropriate uses Extensions" [2] for further guidance regarding appropriate
of SIP. uses of SIP.
Further, it is expected that this mechanism is not to be used in Further, it is expected that this mechanism is not to be used in
applications where the frequency of reportable events is applications where the frequency of reportable events is
excessively rapid (e.g. more than about once per second). A SIP excessively rapid (e.g. more than about once per second). A SIP
network is generally going to be provisioned for a reasonable network is generally going to be provisioned for a reasonable
signalling volume; sending a notification every time a user's GPS signalling volume; sending a notification every time a user's GPS
position changes by one hundreth of a second could easily position changes by one hundreth of a second could easily
overload such a network. overload such a network.
5.2. Event Template-packages 5.2. Event Template-packages
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template-packages. template-packages.
To extend the object-oriented analogy made earlier, event To extend the object-oriented analogy made earlier, event
template-packages can be thought of as templatized C++ packages template-packages can be thought of as templatized C++ packages
which must be applied to other packages to be useful. which must be applied to other packages to be useful.
The name of an event template-package as applied to a package is The name of an event template-package as applied to a package is
formed by appending a period followed by the event formed by appending a period followed by the event
template-package name to the end of the package. For example, if template-package name to the end of the package. For example, if
a template-package called "winfo" were being applied to a package a template-package called "winfo" were being applied to a package
called "presence," the event token used in "Event" and called "presence", the event token used in "Event" and
"Allow-Events" would be "presence.winfo". "Allow-Events" would be "presence.winfo".
Event template-packages must be defined so that they can be Event template-packages must be defined so that they can be
applied to any arbitrary package. In other words, event applied to any arbitrary package. In other words, event
template-packages cannot be specifically tied to one or a few template-packages cannot be specifically tied to one or a few
"parent" packages in such a way that they will not work with "parent" packages in such a way that they will not work with
other packages. other packages.
5.3. Amount of State to be Conveyed 5.3. Amount of State to be Conveyed
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There are two possible solutions to this problem that event There are two possible solutions to this problem that event
packages may choose to implement. packages may choose to implement.
5.3.1. Complete State Information 5.3.1. Complete State Information
For packages which typically convey state information that is For packages which typically convey state information that is
reasonably small (on the order of 1 kb or so), it is suggested reasonably small (on the order of 1 kb or so), it is suggested
that event packages are designed so as to send complete state that event packages are designed so as to send complete state
information when an event occurs. information when an event occurs.
In the circumstances that state may not be sufficient for a In some circumstances, conveying the current state alone may be
particular class of events, the event packages should include insufficient for a particular class of events. In these cases,
complete state information along with the event that occurred. the event packages should include complete state information
For example, "no customer service representatives available" may along with the event that occurred. For example, conveying "no
not be as useful "no customer service representatives available; customer service representatives available" may not be as useful
as conveying "no customer service representatives available;
representative sip:46@cs.xyz.int just logged off". representative sip:46@cs.xyz.int just logged off".
5.3.2. State Deltas 5.3.2. State Deltas
In the case that the state information to be conveyed is large, In the case that the state information to be conveyed is large,
the event package may choose to detail a scheme by which NOTIFY the event package may choose to detail a scheme by which NOTIFY
messages contain state deltas instead of complete state. messages contain state deltas instead of complete state.
Such a scheme would work as follows: any NOTIFY sent in immediate Such a scheme would work as follows: any NOTIFY sent in immediate
response to a SUBSCRIBE contains full state information. NOTIFY response to a SUBSCRIBE contains full state information. NOTIFY
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5.4. Event Package Responsibilities 5.4. Event Package Responsibilities
Event packages are not required to re-iterate any of the behavior Event packages are not required to re-iterate any of the behavior
described in this document, although they may choose to do so for described in this document, although they may choose to do so for
clarity or emphasis. In general, though, such packages are clarity or emphasis. In general, though, such packages are
expected to describe only the behavior that extends or modifies expected to describe only the behavior that extends or modifies
the behavior described in this document. the behavior described in this document.
Note that any behavior designated with "SHOULD" or "MUST" in this Note that any behavior designated with "SHOULD" or "MUST" in this
document is not allowed to be changed by extension documents; document is not allowed to be weakened by extension documents;
however, such documents may elect to strengthen "SHOULD" however, such documents may elect to strengthen "SHOULD"
requirements to "MUST" strength if required by their application. requirements to "MUST" strength if required by their application.
In addition to the normal sections expected by "Instructions to In addition to the normal sections expected by "Instructions
RFC Authors" [5] and "Guidelines for Authors of SIP Extensions" to RFC Authors" [5] and "Guidelines for Authors of SIP
[2] , authors of event packages MUST address each of the issues Extensions" [2], authors of event packages need to address
detailed in the following subsections, whenever applicable. each of the issues detailed in the following subsections,
whenever applicable.
5.4.1. Event Package Name 5.4.1. Event Package Name
This mandatory section of an event package defines the token name This section, which MUST be present, defines the token name to be
to be used to designate the event package. It MUST include the used to designate the event package. It MUST include the
information which appears in the IANA registration of the token. information which appears in the IANA registration of the token.
For information on registering such types, see section 7. For information on registering such types, see section 7.
5.4.2. Event Package Parameters 5.4.2. Event Package Parameters
If parameters are to be used on the "Event" header to modify the If parameters are to be used on the "Event" header to modify the
behavior of the event package, the syntax and semantics of such behavior of the event package, the syntax and semantics of such
headers MUST be clearly defined. headers MUST be clearly defined.
5.4.3. SUBSCRIBE Bodies 5.4.3. SUBSCRIBE Bodies
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package. Such authorization issues may include, for example, package. Such authorization issues may include, for example,
whether all SUBSCRIBE requests for this package are answered with whether all SUBSCRIBE requests for this package are answered with
202 responses (see section 6.2. ). 202 responses (see section 6.2. ).
5.4.7. Notifier generation of NOTIFY requests 5.4.7. Notifier generation of NOTIFY requests
This section of an event package describes the process by which This section of an event package describes the process by which
the notifier generates and sends a NOTIFY request. This includes the notifier generates and sends a NOTIFY request. This includes
detailed information about what events cause a NOTIFY to be sent, detailed information about what events cause a NOTIFY to be sent,
how to compute the state information in the NOTIFY, how to how to compute the state information in the NOTIFY, how to
generate "neutral" or "fake" state information to hide generate neutral or fake state information to hide authorization
authorization delays and decisions from users, and whether state delays and decisions from users, and whether state information is
information is complete or deltas for notifications (see section complete or deltas for notifications; see section 5.3. Such a
5.3. ) section is required.
It may optionally describe the behavior used to processes the This section may optionally describe the behavior used to process
subsequent response. Such a section is required. the subsequent response.
5.4.8. Subscriber processing of NOTIFY requests 5.4.8. Subscriber processing of NOTIFY requests
This section of an event package describes the process followed This section of an event package describes the process followed
by the subscriber upon receipt of a NOTIFY request, including any by the subscriber upon receipt of a NOTIFY request, including any
logic required to form a coherent resource state (if applicable). logic required to form a coherent resource state (if applicable).
5.4.9. Handling of forked requests 5.4.9. Handling of forked requests
Each event package SHOULD specify whether forked SUBSCRIBE Each event package SHOULD specify whether forked SUBSCRIBE
requests are allowed to install multiple subscriptions. requests are allowed to install multiple subscriptions.
If such behavior is not allowed, the first potential If such behavior is not allowed, the first potential
dialog-establishing message will create a dialog. All subsequent dialog-establishing message will create a dialog. All subsequent
NOTIFY messages which correspond to the SUBSCRIBE message (i.e. NOTIFY messages which correspond to the SUBSCRIBE message (i.e.
match To, From, From tag, Call-ID, CSeq, Event, and Event id) but match "To", "From", "From" header "tag" parameter, "Call-ID",
which do not match the dialog would be rejected with a 481 "CSeq", "Event", and "Event" header "id" parameter) but which do
response. not match the dialog would be rejected with a 481 response. Note
that the 200-class response to the SUBSCRIBE can arrive after a
matching NOTIFY has been received; such responses might not
correlate to the same dialog established by the NOTIFY. Except as
required to complete the SUBSCRIBE transaction, such non-matching
200-class responses are ignored.
If installing of multiple subscriptions by way of a single forked If installing of multiple subscriptions by way of a single forked
INVITE is allowed, the subscriber establishes a new dialog SUBSCRIBE is allowed, the subscriber establishes a new dialog
towards each notifier by returning a 200-class response to each towards each notifier by returning a 200-class response to each
NOTIFY. Each dialog is then handled as its own entity, and is NOTIFY. Each dialog is then handled as its own entity, and is
refreshed independent of the other dialogs. refreshed independent of the other dialogs.
In the case that multiple subscriptions are allowed, the event In the case that multiple subscriptions are allowed, the event
package MUST specify whether merging of the notifications to form package MUST specify whether merging of the notifications to form
a single state is required, and how such merging is to be a single state is required, and how such merging is to be
performed. Note that it is possible that some event packages may performed. Note that it is possible that some event packages may
be defined in such a way that each dialog is tied to a mutually be defined in such a way that each dialog is tied to a mutually
exclusive state which is unaffected by the other dialogs; this exclusive state which is unaffected by the other dialogs; this
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MUST strength) which defines an absolute maximum on the rate at MUST strength) which defines an absolute maximum on the rate at
which notifications are allowed to be generated by a single which notifications are allowed to be generated by a single
notifier. notifier.
Such packages MAY further define a throttle mechanism which Such packages MAY further define a throttle mechanism which
allows subscribers to further limit the rate of notification. allows subscribers to further limit the rate of notification.
5.4.11. State Agents 5.4.11. State Agents
Designers of event packages should consider whether their package Designers of event packages should consider whether their package
can benefit from network aggregation points ("State Agents") can benefit from network aggregation points (state agents) and/or
and/or nodes which act on behalf of other nodes. (For example, nodes which act on behalf of other nodes. (For example, nodes
nodes which provide state information about a resource when such which provide state information about a resource when such a
a resource is unable or unwilling to provide such state resource is unable or unwilling to provide such state information
information itself). An example of such an application is a node itself). An example of such an application is a node which tracks
which tracks the presence and availability of a user in the the presence and availability of a user in the network.
network.
If state agents are to be used by the package, the package MUST If state agents are to be used by the package, the package MUST
specify how such state agents aggregate information and how they specify how such state agents aggregate information and how they
provide authentication and authorization. provide authentication and authorization.
Event packages MAY also outline specific scenarios under which Event packages MAY also outline specific scenarios under which
notifier migrations take place. notifier migrations take place.
5.4.12. Examples 5.4.12. Examples
skipping to change at page 26, line 48 skipping to change at page 27, line 49
To prevent such attacks, implementations SHOULD require To prevent such attacks, implementations SHOULD require
authentication. Authentication issues are discussed in SIP [1] . authentication. Authentication issues are discussed in SIP [1] .
6.5. Man-in-the middle attacks 6.5. Man-in-the middle attacks
Even with authentication, man-in-the-middle attacks using Even with authentication, man-in-the-middle attacks using
SUBSCRIBE may be used to install arbitrary subscriptions, hijack SUBSCRIBE may be used to install arbitrary subscriptions, hijack
existing subscriptions, terminate outstanding subscriptions, or existing subscriptions, terminate outstanding subscriptions, or
modify the resource to which a subscription is being made. To modify the resource to which a subscription is being made. To
prevent such attacks, implementations SHOULD provide integrity prevent such attacks, implementations SHOULD provide integrity
protection across "Contact," "Route," "Expires," "Event," and protection across "Contact", "Route", "Expires", "Event", and
"To" headers of SUBSCRIBE messages, at a minimum. If SUBSCRIBE "To" headers of SUBSCRIBE messages, at a minimum. If SUBSCRIBE
bodies are used to define further information about the state of bodies are used to define further information about the state of
the call, they SHOULD be included in the integrity protection the call, they SHOULD be included in the integrity protection
scheme. scheme.
Man-in-the-middle attacks may also attempt to use NOTIFY messages Man-in-the-middle attacks may also attempt to use NOTIFY messages
to spoof arbitrary state information and/or terminate outstanding to spoof arbitrary state information and/or terminate outstanding
subscriptions. To prevent such attacks, implementations SHOULD subscriptions. To prevent such attacks, implementations SHOULD
provide integrity protection across the "Call-ID," "CSeq," and provide integrity protection across the "Call-ID", "CSeq", and
"Subscription-State" headers and the bodies of NOTIFY messages. "Subscription-State" headers and the bodies of NOTIFY messages.
Integrity protection of message headers and bodies is discussed Integrity protection of message headers and bodies is discussed
in SIP [1] . in SIP [1] .
6.6. Confidentiality 6.6. Confidentiality
The state information contained in a NOTIFY message has the The state information contained in a NOTIFY message has the
potential to contain sensitive information. Implementations MAY potential to contain sensitive information. Implementations MAY
encrypt such information to ensure confidentiality. encrypt such information to ensure confidentiality.
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As this document specifies no package or template-package names, As this document specifies no package or template-package names,
the initial IANA registration for event types will be empty. The the initial IANA registration for event types will be empty. The
remainder of the text in this section gives an example of the remainder of the text in this section gives an example of the
type of information to be maintained by the IANA; it also type of information to be maintained by the IANA; it also
demonstrates all five possible permutations of package type, demonstrates all five possible permutations of package type,
contact, and reference. contact, and reference.
The table below lists the event packages and template-packages The table below lists the event packages and template-packages
defined in "SIP-Specific Event Notification" [RFC xxxx]. Each defined in "SIP-Specific Event Notification" [RFC xxxx]. Each
name is designated as a package or a template-package under name is designated as a package or a template-package under
"Type." "Type".
Package Name Type Contact Reference Package Name Type Contact Reference
------------ ---- ------- --------- ------------ ---- ------- ---------
example1 package [Roach] example1 package [Roach]
example2 package [Roach] [RFC xxxx] example2 package [Roach] [RFC xxxx]
example3 package [RFC xxxx] example3 package [RFC xxxx]
example4 template [Roach] [RFC xxxx] example4 template [Roach] [RFC xxxx]
example5 template [RFC xxxx] example5 template [RFC xxxx]
PEOPLE PEOPLE
skipping to change at page 29, line 30 skipping to change at page 30, line 30
7.3. Syntax 7.3. Syntax
This section describes the syntax extensions required for event This section describes the syntax extensions required for event
notification in SIP. Semantics are described in section 4. Note notification in SIP. Semantics are described in section 4. Note
that the formal syntax definitions described in this document are that the formal syntax definitions described in this document are
expressed in the ABNF format defined by [1] , and contain expressed in the ABNF format defined by [1] , and contain
references to elements defined therein. references to elements defined therein.
7.4. New Methods 7.4. New Methods
This document describes two new SIP methods: "SUBSCRIBE" and This document describes two new SIP methods: SUBSCRIBE and
"NOTIFY." NOTIFY.
This table expands on tables 2 and 3 in SIP [1] . This table expands on tables 2 and 3 in SIP [1] .
Header Where SUB NOT Header Where SUB NOT
------ ----- --- --- ------ ----- --- ---
Accept R o o Accept R o o
Accept 2xx - - Accept 2xx - -
Accept 415 o o Accept 415 o o
Accept-Encoding R o o Accept-Encoding R o o
Accept-Encoding 2xx - - Accept-Encoding 2xx - -
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Contact 485 o o Contact 485 o o
Content-Disposition o o Content-Disposition o o
Content-Encoding o o Content-Encoding o o
Content-Language o o Content-Language o o
Content-Length t t Content-Length t t
Content-Type * * Content-Type * *
CSeq c m m CSeq c m m
Date o o Date o o
Error-Info 300-699 o o Error-Info 300-699 o o
Expires o - Expires o -
Expires 2xx m -
From c m m From c m m
In-Reply-To R - - In-Reply-To R - -
Max-Forwards R m m Max-Forwards R m m
Min-Expires 423 m - Min-Expires 423 m -
MIME-Version o o MIME-Version o o
Organization o - Organization o -
Priority R o - Priority R o -
Proxy-Authenticate 407 m m Proxy-Authenticate 407 m m
Proxy-Authorization R o o Proxy-Authorization R o o
Proxy-Require R o o Proxy-Require R o o
skipping to change at page 30, line 52 skipping to change at page 32, line 4
RSeq 1xx o o RSeq 1xx o o
Server r o o Server r o o
Subject R - - Subject R - -
Supported R o o Supported R o o
Supported 2xx o o Supported 2xx o o
Timestamp o o Timestamp o o
To c(1) m m To c(1) m m
Unsupported 420 o o Unsupported 420 o o
User-Agent o o User-Agent o o
Via c m m Via c m m
Warning R - o
Warning r o o Warning r o o
WWW-Authenticate 401 m m WWW-Authenticate 401 m m
7.4.1. SUBSCRIBE method 7.4.1. SUBSCRIBE method
"SUBSCRIBE" is added to the definition of the element "Method" in "SUBSCRIBE" is added to the definition of the element "Method" in
the SIP message grammar. the SIP message grammar.
Like all SIP method names, the SUBSCRIBE method name is case Like all SIP method names, the SUBSCRIBE method name is case
sensitive. The SUBSCRIBE method is used to request asynchronous sensitive. The SUBSCRIBE method is used to request asynchronous
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Header field where proxy ACK BYE CAN INV OPT REG PRA SUB NOT Header field where proxy ACK BYE CAN INV OPT REG PRA SUB NOT
----------------------------------------------------------------- -----------------------------------------------------------------
Allow-Events R o o - o o o o o o Allow-Events R o o - o o o o o o
Allow-Events 2xx - o - o o o o o o Allow-Events 2xx - o - o o o o o o
Allow-Events 489 - - - - - - - m m Allow-Events 489 - - - - - - - m m
Event R - - - - - - - m m Event R - - - - - - - m m
Subscription-State R - - - - - - - - m Subscription-State R - - - - - - - - m
7.5.1. "Event" header 7.5.1. "Event" header
The following header is defined for the purposes of this
specification.
Event = ( "Event" | "o" ) HCOLON event-type
*( SEMI event-param )
event-type = event-package *( "." event-template )
event-package = token-nodot
event-template = token-nodot
token-nodot = 1*( alphanum | "-" | "!" | "%" | "*"
| "_" | "+" | "`" | "'" | "~" )
event-param = generic-param | ( "id" EQUAL token )
Event is added to the definition of the element "message-header" Event is added to the definition of the element "message-header"
in the SIP message grammar. in the SIP message grammar.
For the purposes of matching responses and NOTIFY messages with For the purposes of matching responses and NOTIFY messages with
SUBSCRIBE messages, the event-type portion of the "Event" header SUBSCRIBE messages, the event-type portion of the "Event" header
is compared byte-by-byte, and the "id" parameter token (if is compared byte-by-byte, and the "id" parameter token (if
present) is compared byte-by-byte. An "Event" header containing present) is compared byte-by-byte. An "Event" header containing
an "id" parameter never matches an "Event" header without an "id" an "id" parameter never matches an "Event" header without an "id"
parameter. No other parameters are considered when performing a parameter. No other parameters are considered when performing a
comparison. comparison.
Note that the forgoing text means that "Event: foo; id=1234"
would match "Event: foo; param=abcd; id=1234", but not
"Event: foo" (id does not match) or "Event: Foo; id=1234"
(event portion does not match).
This document does not define values for event-types. These This document does not define values for event-types. These
values will be defined by individual event packages, and MUST be values will be defined by individual event packages, and MUST be
registered with the IANA. registered with the IANA.
There MUST be exactly one event type listed per event header. There MUST be exactly one event type listed per event header.
Multiple events per message are disallowed. Multiple events per message are disallowed.
For the curious, the "o" short form is chosen to represent
"occurrence."
7.5.2. "Allow-Events" Header 7.5.2. "Allow-Events" Header
The following header is defined for the purposes of this Allow-Events is added to the definition of the element
specification. "general-header" in the SIP message grammar. Its usage is
describe in section 4.3.7.
Allow-Events = ( "Allow-Events" | "u" ) HCOLON 7.5.3. "Subscription-State" Header
1*event-type
Allow-Events is added to the definition of the element Subscription-State is added to the definition of the element
"general-header" in the SIP message grammar. "request-header" in the SIP message grammar. Its usage is
described in section 4.2.4.
For the curious, the "u" short form is chosen to represent 7.6. New Response Codes
"understands."
7.5.3. "Subscription-State" Header 7.6.1. "202 Accepted" Response Code
The following header is defined for the purposes of this The 202 response is added to the "Success" header field
specification. definition. "202 Accepted" has the same meaning as that defined
in HTTP/1.1 [4].
Subscription-State = "Subscription-State" HCOLON 7.6.2. "489 Bad Event" Response Code
substate-value )
*( SEMI subexp-params )
substate-value = "active" | "pending" | "terminated" The 489 event response is added to the "Client-Error" header
subexp-params = ("reason" EQUAL reason-code) field definition. "489 Bad Event" is used to indicate that the
|("expires" EQUAL delta-seconds) server did not understand the event package specified in a
|("retry-after" EQUAL delta-seconds) "Event" header field.
| generic-param
reason-code = "deactivated" 7.7. Augmented BNF Definitions
| "probation"
| "rejected"
| "timeout"
| "giveup"
| reason-extension
The Augmented BNF definitions for the various new and modified
syntax elements follows. The notation is as used in SIP [1], and
any elements not defined in this section are as defined in SIP
and the documents to which it refers.
SUBSCRIBEm = %x53.55.42.53.43.52.49.42.45 ; SUBSCRIBE in caps
NOTIFYm = %x4E.4F.54.49.46.59 ; NOTIFY in caps
extension-method = SUBSCRIBEm / NOTIFYm / token
Event = ( "Event" / "o" ) HCOLON event-type
*( SEMI event-param )
event-type = event-package *( "." event-template )
event-package = token-nodot
event-template = token-nodot
token-nodot = 1*( alphanum / "-" / "!" / "%" / "*"
/ "_" / "+" / "`" / "'" / "~" )
event-param = generic-param / ( "id" EQUAL token )
Allow-Events = ( "Allow-Events" / "u" ) HCOLON event-type
*(COMMA event-type)
Subscription-State = "Subscription-State" HCOLON substate-value
*( SEMI subexp-params )
substate-value = "active" / "pending" / "terminated"
/ extension-substate
extension-substate = token
subexp-params = ("reason" EQUAL reason-value)
/ ("expires" EQUAL delta-seconds)
/ ("retry-after" EQUAL delta-seconds)
/ generic-param
reason-value = "deactivated"
/ "probation"
/ "rejected"
/ "timeout"
/ "giveup"
/ reason-extension
reason-extension = token reason-extension = token
Subscription-State is added to the definition of the element 8. Changes
"request-header" in the SIP message grammar.
7.6. New Response Codes 8.1. Changes from draft-ietf-...-02
7.6.1. "202 Accepted" Response Code - Fixes in section
4.1.1.
to align with rest of spec:
missed one reference to notifier being able to increase
subscription interval.
The 202 response is added to the "Success" header field - Changed Record-Routing description in
definition: 4.1.5.
and
Success = "200" ; OK 4.2.3.
| "202" ; Accepted
"202 Accepted" has the same meaning as that defined in HTTP/1.1 Now mandatory only for 1st SUBSCRIBE and
[4] . dialog-establishing NOTIFY messages.
7.6.2. "489 Bad Event" Response Code - Added language to
4.2.4.
requiring an immediate
NOTIFY response.
The 489 event response is added to the "Client-Error" header - Added clarifying text to
field definition: 4.3.3.
to explain that
the forking behavior comes from the SIP spec.
Client-Error = "400" ; Bad Request - Fixed ABNF to use "/" instead of "|". Other minor
... ABNF updates to make consistent and correct.
| "489" ; Bad Event
"489 Bad Event" is used to indicate that the server did not - Grouped ABNF into a single section.
understand the event package specified in a "Event" header field.
8. Changes - Pointed to correct version of HTTP/1.1 spec.
8.1. Changes from draft-ietf-...-01 - Added generation of 423 error response to
- Changed dependancy from RFC2543 to new sip bis draft. notifier handling of SUBSCRIBE requests.
- Update to allow "Warning" headers in NOTIFY
requests
- Several small editorial changes.
- Adjusted usage of quotation marks next to periods and
commas to match that used by the American Mathematical
Society; although contrary to traditional American
English convention, this usage lends clarity to certain
passages.
8.2. Changes from draft-ietf-...-01
- Changed dependency from RFC2543 to new sip bis draft.
This allowed removal of certain sections of text. This allowed removal of certain sections of text.
- Renamed "sub-packages" to "template-packages" in an - Renamed "sub-packages" to "template-packages" in an
attempt to mitigate exploding rampant misinterpretation. attempt to mitigate exploding rampant misinterpretation.
- Changed "Subscription-Expires" to "Subscription-State," - Changed "Subscription-Expires" to "Subscription-State",
and added clearer semantics for "reason" codes. and added clearer semantics for "reason" codes.
- Aligned "Subscription-State" "reason" codes with - Aligned "Subscription-State" "reason" codes with
watcherinfo draft. watcherinfo draft.
- Made "Subscription-State" mandatory in NOTIFY - Made "Subscription-State" mandatory in NOTIFY
requests, since it is integral to defining the requests, since it is integral to defining the
creation and destruction of subscriptions (and, creation and destruction of subscriptions (and,
consequently, dialogs) consequently, dialogs)
- Heavily revised section on dialog creation and - Heavily revised section on dialog creation and
termination. termination.
- Expanded migration section. - Expanded migration section.
- Added "id" parameter to Event header, to allow - Added "id" parameter to Event header, to allow
demultiplexing of NOTIFY requests when more than demultiplexing of NOTIFY requests when more than
one subscription is associated with a single dialog. one subscription is associated with a single dialog.
- Syncronized SUBSCRIBE "Expires" handling with REGISTER - Synchronized SUBSCRIBE "Expires" handling with REGISTER
(again) (again)
- Added definitions section. - Added definitions section.
- Restructuring for clarity. - Restructuring for clarity.
- Added statement explicitly allowing event - Added statement explicitly allowing event
packages to define additional parameters packages to define additional parameters
for the "Event" header. for the "Event" header.
- Added motivational text in several places. - Added motivational text in several places.
- Synced up header table modifications with bis draft. - Synced up header table modifications with bis draft.
8.2. Changes from draft-ietf-...-00 8.3. Changes from draft-ietf-...-00
- Fixed confusing typo in section describing correlation - Fixed confusing typo in section describing correlation
of SUBSCRIBE requests of SUBSCRIBE requests
- Added explanitory text to clarify tag handling when - Added explanatory text to clarify tag handling when
generating re-subscriptions generating re-subscriptions
- Expanded general handling section to include specific - Expanded general handling section to include specific
discussion of Route/Record-Route handling. discussion of Route/Record-Route handling.
- Included use of "methods" parameter on Contact as - Included use of "methods" parameter on Contact as
a means for detecting support for SUBSCRIBE and NOTIFY. a means for detecting support for SUBSCRIBE and NOTIFY.
- Added definition of term "dialog"; changed "leg" to - Added definition of term "dialog"; changed "leg" to
"dialog" everwhere. "dialog" everywhere.
- Added syntax for "Subscription-Expires" header. - Added syntax for "Subscription-Expires" header.
- Changed NOTIFY messages to refer to "Subscription-Expires" - Changed NOTIFY messages to refer to "Subscription-Expires"
everywhere (instead of "Expires.") everywhere (instead of "Expires".)
- Added information about generation and handling of - Added information about generation and handling of
481 responses to SUBSCRIBE requests 481 responses to SUBSCRIBE requests
- Changed having Expires header in SUBSCRIBE from - Changed having Expires header in SUBSCRIBE from
MUST to SHOULD; this aligns more closely with MUST to SHOULD; this aligns more closely with
REGISTER behavior REGISTER behavior
- Removed experimental/private event package names, - Removed experimental/private event package names,
per list consensus per list consensus
skipping to change at page 36, line 24 skipping to change at page 38, line 21
with other parts of this document. with other parts of this document.
- Moved description of event packages to later in document, - Moved description of event packages to later in document,
to reduce the number of forward references. to reduce the number of forward references.
- Minor editorial and nits changes - Minor editorial and nits changes
- Added new open issues to open issues section. All - Added new open issues to open issues section. All
previous open issues have been resolved. previous open issues have been resolved.
8.3. Changes from draft-roach-...-03
- Added DOS attacks section to open issues.
- Added discussion of forking to open issues
- Changed response to PINT request for notifiers who don't
support PINT from 400 to 489.
- Added sentence to security section to call attention to
potential privacy issues of delayed NOTIFY responses.
- Added clarification: access control list handling is out
of scope.
- (Hopefully) Final resolution on out-of-band subscriptions:
mentioned in section
4.2.
Removed from open issues.
- Made "Contact" header optional for SUBSCRIBE 1xx responses.
- Added description clarifying tag handling (section
4.3.4.
)
- Removed event throttling from open issues.
- Editorial cleanup to remove term "extension draft" and
similar; "event package" is now (hopefully) used consistently
throughout the document.
- Remove discussion of event agents from open issues.
This is covered in the event packages section now.
- Added discussion of forking to open issues.
- Added discussion of sub-packages
- Added clarification that, upon receiving a "NOTIFY"
with an expires of "0", the subscriber can re-subscribe.
This allows trivial migration of subscriptions between
nodes.
- Added preliminary IANA Considerations section
- Changed syntax for experimental event tokens to avoid
possibly ambiguity between experimental tokens and
sub-packages.
- Slight adjustment to "Event" syntax to accommodate sub-packages.
- Added section describing the information which is to be
included in documents describing event packages.
- Made 481 responses mandatory for unexpected notifications
(allowing notifiers to remove subscriptions in error cases)
- Several minor non-semantic editorial changes.
8.4. Changes from draft-roach-...-02
- Clarification under "Notifier SUBSCRIBE behavior" which
indicates that the first NOTIFY message (sent immediately
in response to a SUBSCRIBE) may contain an empty body, if
resource state doesn't make sense at that point in time.
- Text on message flow in overview section corrected
- Removed suggestion that clients attempt to unsubscribe
whenever they receive a NOTIFY for an unknown event.
Such behavior opens up DOS attacks, and will lead to
message loops unless additional precautions are taken.
The 481 response to the NOTIFY should serve the same
purpose.
- Changed processing of non-200 responses to NOTIFY from
"SHOULD remove contact" to "MUST remove contact" to support
the above change.
- Re-added discussion of out-of-band subscription mechanisms
(including open issue of resource identification).
- Added text specifying that SUBSCRIBE transactions are not
to be prolonged. This is based on the consensus that non-INVITE
transactions should never be prolonged; such consensus within
the SIP working group was reached at the 49th IETF.
- Added "202 Accepted" response code to support the above
change. The behavior of this 202 response code is a
generalization of that described in the presence draft.
- Updated to specify that the response to an unauthorized
SUBSCRIBE request is 603 or 403.
- Level-4 subheadings added to particularly long sections to
break them up into logical units. This helps make the
behavior description seem somewhat less rambling. This also
caused some re-ordering of these paragraphs (hopefully in a
way that makes them more readable).
- Some final mopping up of old text describing "call related"
and "third party" subscriptions (deprecated concepts).
- Duplicate explanation of subscription duration removed from
subscriber SUBSCRIBE behavior section.
- Other text generally applicable to SUBSCRIBE (instead of just
subscriber handling of SUBSCRIBE) moved to parent section.
- Updated header table to reflect mandatory usage of "Expires"
header in SUBSCRIBE requests and responses
- Removed "Event" header usage in responses
- Added sentence suggesting that notifiers may notify
subscribers when a subscription has timed out.
- Clarified that a failed attempt to refresh a subscription
does not imply that the original subscription has been
cancelled.
- Clarified that 489 is a valid response to "NOTIFY" requests.
- Minor editorial changes to clean up awkward and/or unclear
grammar in several places
8.5. Changes from draft-roach-...-01
- Multiple contacts per SUBSCRIBE message disallowed.
- Contact header now required in NOTIFY messages.
- Distinction between third party/call member events removed.
- Distinction between call-related/resource-related events removed.
- Clarified that subscribers must expect NOTIFY messages before
the SUBSCRIBE transaction completes
- Added immediate NOTIFY message after successful SUBSCRIBE;
this solves a myriad of issues, most having to do with forking.
- Added discussion of "undefined state" (before a NOTIFY arrives).
- Added mechanism for notifiers to shorten/cancel outstanding
subscriptions.
- Removed open issue about appropriateness of new "489" response.
- Removed all discussion of out-of-band subscriptions.
- Added brief discussion of event state polling.
9. References 9. References
[1] J. Rosenberg et. al., "SIP: Session Initiation Protocol", [1] J. Rosenberg et. al., "SIP: Session Initiation Protocol",
<draft-ietf-sip-rfc2543bis-07>, IETF; February 2002. Work in <draft-ietf-sip-rfc2543bis-07>, IETF; February 2002. Work in
progress. progress.
[2] J. Rosenberg, H. Schulzrinne, "Guidelines for Authors of SIP [2] J. Rosenberg, H. Schulzrinne, "Guidelines for Authors of SIP
Extensions", <draft-ietf-sip-guidelines-03.txt>, IETF; Extensions", <draft-ietf-sip-guidelines-03.txt>, IETF;
November 2001. Work in progress. November 2001. Work in progress.
[3] S. Petrack, L. Conroy, "The PINT Service Protocol", RFC 2848, [3] S. Petrack, L. Conroy, "The PINT Service Protocol", RFC 2848,
IETF; June 2000. IETF; June 2000.
[4] R. Fielding et. al., "Hypertext Transfer Protocol -- [4] R. Fielding et. al., "Hypertext Transfer Protocol --
HTTP/1.1", RFC2068, IETF, January 1997. HTTP/1.1", RFC 2616, IETF, June 1999.
[5] J. Postel, J. Reynolds, "Instructions to RFC Authors", [5] J. Postel, J. Reynolds, "Instructions to RFC Authors", RFC
RFC2223, IETF, October 1997. 2223, IETF, October 1997.
[6] T. Narten, H. Alvestrand, "Guidelines for Writing an IANA [6] T. Narten, H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, IETF, October 1998. Considerations Section in RFCs", BCP 26, IETF, October 1998.
[7] Schulzrinne/Rosenberg, "SIP Caller Preferences and Callee [7] Schulzrinne/Rosenberg, "SIP Caller Preferences and Callee
Capabilities", <draft-ietf-sip-callerprefs-05.txt>, IETF; Capabilities", <draft-ietf-sip-callerprefs-05.txt>, IETF;
November 2001. Work in progress. November 2001. Work in progress.
[8] S. Bradner, "Key words for use in RFCs to indicate
requirement levels", RFC 2119, IETF, March 1997
10. Acknowledgements 10. Acknowledgements
Thanks to the participants in the Events BOF at the 48th IETF Thanks to the participants in the Events BOF at the 48th IETF
meeting in Pittsburgh, as well as those who gave ideas and meeting in Pittsburgh, as well as those who gave ideas and
suggestions on the SIP Events mailing list. In particular, I wish suggestions on the SIP Events mailing list. In particular, I wish
to thank Henning Schulzrinne of Columbia University for coming up to thank Henning Schulzrinne of Columbia University for coming up
with the final three-tiered event identification scheme, Sean with the final three-tiered event identification scheme, Sean
Olson for miscellaneous guidance, Jonathan Rosenberg for a Olson for miscellaneous guidance, Jonathan Rosenberg for a
thorough scrubbing of the -00 draft, and the authors of the "SIP thorough scrubbing of the -00 draft, and the authors of the "SIP
 End of changes. 

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