Network Working Group A. Niemi
Internet-Draft Nokia
Intended status: Standards Track May 2, 2007
Expires: November 3, 2007
An Extension to Session Initiation Protocol (SIP) Events for Conditional
Event Notification
draft-ietf-sip-subnot-etags-00
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
The Session Initiation Protocol (SIP) events framework enables
receiving asynchronous notification of various events from other SIP
user agents. This framework defines the procedures for creating,
refreshing and terminating subscriptions, as well as fetching and
periodic polling of resource state. These procedures have a serious
deficiency in that they do not allow state to persist over a
subscription refresh, or between two consecutive polls. This
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inability to suppress notifications of state already known to the
subscriber results in superfluous traffic in the network. This memo
defines an extension to SIP events that allows the subscriber to
condition the subscription request to whether the state has changed
since the previous notification was received. When such a condition
is true, either the body of an event notification or the entire
notification message is suppressed.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Document Conventions . . . . . . . . . . . . . . . . . . . 4
2. Motivations and Background . . . . . . . . . . . . . . . . . . 5
2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Problem Description . . . . . . . . . . . . . . . . . . . 5
2.3. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6
3. Overview of Operation . . . . . . . . . . . . . . . . . . . . 7
4. Subscriber Behavior . . . . . . . . . . . . . . . . . . . . . 10
4.1. Indicating Support for Entity Tags . . . . . . . . . . . . 10
4.2. Generating Conditional SUBSCRIBEs . . . . . . . . . . . . 10
4.3. Polling or Fetching Resource State . . . . . . . . . . . . 11
4.4. Resuming a Subscription . . . . . . . . . . . . . . . . . 13
4.5. Refreshing a Subscription . . . . . . . . . . . . . . . . 14
4.6. Terminating a Subscription . . . . . . . . . . . . . . . . 14
5. Notifier Behavior . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Generating Entity-tags . . . . . . . . . . . . . . . . . . 15
5.2. Suppressing NOTIFY Bodies . . . . . . . . . . . . . . . . 16
5.3. Suppressing NOTIFY Requests . . . . . . . . . . . . . . . 16
5.4. State Differentials . . . . . . . . . . . . . . . . . . . 17
5.5. List Subscriptions . . . . . . . . . . . . . . . . . . . . 17
6. Protocol Element Definitions . . . . . . . . . . . . . . . . . 17
6.1. 204 (No Notification) Response Code . . . . . . . . . . . 17
6.2. Suppress-Notify-If-Match Header Field . . . . . . . . . . 18
6.3. Suppress-Body-If-Match Header Field . . . . . . . . . . . 18
6.4. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Open Issues and Todo . . . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
8.1. "subnot-etags" Option Tag . . . . . . . . . . . . . . . . 19
8.2. 204 (No Notification) Response Code . . . . . . . . . . . 19
8.3. Suppress-Body-If-Match Header Field . . . . . . . . . . . 19
8.4. Suppress-Notify-If-Match Header Field . . . . . . . . . . 20
9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Normative References . . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21
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Intellectual Property and Copyright Statements . . . . . . . . . . 22
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1. Introduction
The Session Initiation Protocol (SIP) events framework provides an
extensible facility for requesting notification of certain events
from other SIP user agents. This framework includes procedures for
creating, refreshing and terminating of subscriptions, as well as the
possibility to fetch or periodically poll the event resource.
Several instantiations of this framework, called event packages have
been defined, e.g., for presence [6], message waiting indications [7]
and registrations [8].
By default, every SUBSCRIBE request generates a NOTIFY request
containing the latest event state. Typically, a SUBSCRIBE request is
issued whenever a subscription is installed, periodically refreshed
or terminated. Once the subscription has been installed, the
majority of the NOTIFYs generated by the subscription refreshes are
superfluous; the subscriber usually is in possession of the event
state already, except in the unlikely case where a state change
exactly coincides with the periodic subscription refresh. In most
cases, the final event state generated upon terminating the
subscription similarly contains resource state that the subscriber
already has.
Fetching or polling of resource state behaves in a similarly
suboptimal way in cases where the state has not changed since the
previous poll occurred. In general, the problem lies in with the
inability to persist state across a SUBSCRIBE request.
This memo defines an extension to the SIP events framework allowing a
notifier to issue versioning in the form of entity tags to
notifications, and the subscriber to condition the SUBSCRIBE request
for actual changes since the last notification carrying that entity
tag was issued. The solution is almost identical to conditional
requests defined in the HyperText Transfer Protocol (HTTP) [9], and
follows the mechanism already defined for the PUBLISH [1] method for
issuing conditional event publications.
1.1. Document Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119 [2]
and indicate requirement levels for compliant implementations.
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2. Motivations and Background
2.1. Overview
A SUBSCRIBE request creates a subscription with a finite lifetime.
This lifetime is negotiated using the Expires header field, and
unless the subscription is refreshed by the subscriber before the
expiration is met, the subscription is terminated. The frequency of
these subscription refreshes depends on the event package, and
typically ranges from minutes to hours.
Changes in connectivity represent another impetus for a subscriber
re-subscribing. If the subscriber's point of attachment to the
Internet changes, e.g., due to dynamic address allocation, the
subscriber needs to re-subscribe in order to update the dialog
endpoint, which is carried in the Contact header field of the
SUBSCRIBE request.
Another option for reducing connectivity induced subscription
refreshes is to use the Globally Routable User Agent (UA) URI
(GRUU) [10] as a stable endpoint contact for subscriptions.
2.2. Problem Description
In spite of being somewhat distinct operations, the SIP events
framework does not include different protocol methods for initiating
and terminating of subscriptions, subscription refreshes and fetches
inside and outside of the SIP dialog. Instead, the SUBSCRIBE method
is overloaded to perform all of these functions, and the notifier
behavior is identical in each of them; each SUBSCRIBE request
generates a NOTIFY request containing the latest resource state. In
fact, the only difference between a fetch that does not create a
(lasting) subscription, and a SUBSCRIBE that creates one is in the
Expires header field value of the SUBSCRIBE; a zero-expiry SUBSCRIBE
only generates a single NOTIFY, after which the subscription
immediately terminates.
Some subscriber implementations may choose to operate in semi-
stateless mode, in which they immediately upon receiving and
processing the NOTIFY forget the resource state. This operation
necessarily needs every NOTIFY to carry the full resource state.
However, for an implementation that stores the resource state
locally, this mode of operation is inefficient.
There are certain conditions that aggravate the problem. Such
conditions usually entail such things as:
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o Large entity bodies in the payloads of notifications
o High rate of subscription refreshes
o Relatively low rate of actual notifications triggered by actual
state changes
In effect, for an event package that generates few state changes, and
is refreshed relatively often the majority of traffic generated may
be related to subscription maintenance. Especially in networks where
bandwidth consumption and traffic count is at a premium, the high
overhead of subscription maintenance becomes a barrier for
deployment.
The same problem affects fetching and polling of resource state as
well. As a benchmark, if we look at the performance of HTTP [9] in
similar scenarios, it performs substantially better using conditional
requests. When resources are tagged with an entity-tag, and each GET
is a conditional one using the "If-None-Match" header field, the
entity body need not be sent more than once; if the resource has not
changed between successive polls, an error response is returned
indicating this fact, and the resource entity is not transmitted
again.
The SIP PUBLISH [1] method also contains a similar feature, where a
refresh of a publication is done by reference to its assigned entity-
tag, instead of retransmitting the event state each time the
publication expiration is extended.
2.3. Requirements
As a summary, here is the required functionality to solve the
presented issues:
REQ1: It must be possible to suppress the NOTIFY request (or at a
minimum the event body therein) if the subscriber is already
in possession of the latest event state of the resource.
REQ2: This mechanism must apply to initial subscriptions, in which
the subscriber is attempting to "resume" an earlier
subscription.
REQ3: This mechanism must apply to refreshing a subscription.
REQ4: This mechanism must apply to terminating a subscription
(i.e., an unsubscribe).
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REQ5: This mechanism must apply to fetching or polling of resource
state.
3. Overview of Operation
Whenever a subscriber initiates a subscription, it issues a SUBSCRIBE
request. If the subscriber supports the conditional subscription
mechanism described in this memo, it can include a "subnot-etags" tag
in the Supported header field. The SUBSCRIBE request is sent, routed
and processed by the notifier normally, i.e., according to RFC3261
[3], RFC3265 [4].
If the notifier receiving the SUBSCRIBE request supports conditional
subscriptions, it generates a unique entity tag for the resource
state, and attaches that tag in a SIP-ETag header field of every
NOTIFY request. The entity tag is unique for that particular
resource and event notification.
Entity-tags are independent of subscriptions; the notifier remembers
the entity-tag of the resource state regardless of whether or not
there are any active subscription to that resource. This allows
notifications generated to a fetch or a poll to have valid entity-
tags even across subsequent fetches of the resource state.
The subscriber will store the entity-tag received in the notification
along with the resource state. It can then later use this entity-tag
to make a SUBSCRIBE contain a condition in the form of a header
field. Unlike the "If-Match" condition in a PUBLISH [1] request,
which applies to whether the PUBLISH succeeds or returns an error,
this condition applies to the notifications that are sent after the
SUBSCRIBE request has been processed.
The two types of conditions available for a SUBSCRIBE are a Suppress-
Body-If-Match and a Suppress-Notify-If-Match; each of these header
fields contains the last entity-tag seen by the subscriber. If the
condition evaluates to true, the first of these conditions will
instruct the notifier to suppress the body of the next notification
and the second the entire notification. The condition is evaluated
by matching the value of the header field against the current entity-
tag of the resource state. There is also a wildcard entity-tag with
a special value of "*" that always matches.
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Subscriber Notifier
---------- --------
(1) SUBSCRIBE -------->
Supported: subnot-etags
Expires: 3600
<-------- (2) 202
<-------- (3) NOTIFY
SIP-ETag: ffee2
(4) 200 -------->
...
(5) SUBSCRIBE --------> \ if "ffee2"
Suppress-Notify-If-Match: ffee2 | matches
Supported: subnot-etags | local
Expires: 3600 | entity-tag
|
<-------- (6) 204 / then
...
<-------- (7) NOTIFY
SIP-ETag: ca89a
(8) 200 -------->
...
(9) SUBSCRIBE --------> \ if "ca89"
Suppress-Notify-If-Match: ca89a | matches
Supported: subnot-etags | local
Expires: 0 | entity-tag
|
<-------- (10) 204 / then
Figure 1: Example Message Flow
Figure 1 describes a typical message flow for conditional SUBSCRIBEs:
1. The subscriber initiates a subscription by sending a SUBSCRIBE
request for a resource. The request can contain a Supported tag
of "subnot-etags" to indicate support for conditional
subscriptions.
2. After proper authentication and authorization, the the notifier
accepts the subscription.
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3. The notifier then immediately sends the initial resource state
in a notification. And since the subscriber supports the
mechanism, it includes a resource-specific entity-tag in a SIP-
ETag header field.
4. The subscriber accepts the notification and stores the entity-
tag value along with the resource state.
5. Later, the subscriber refreshes the subscription by a
reSUBSCRIBE, and includes an entity-tag in a Suppress-Notify-If-
Match header field.
6. The notifier evaluates the condition by matching its entity-tag
for the resource against the value of the Suppress-Notify-If-
Match header field. If the condition evaluates to true, the
notifier informs the subscriber that the notification was
blocked.
7. At some point, the state of the resource changes, e.g., the
presence status of a user changes from online to busy. This
triggers an event notification with a new value in the SIP-ETag
header field.
8. The subscriber accepts the notification and stores the new
entity-tag along with the resource state.
9. After a while, the subscriber decides to terminate the
subscription with an unSUBSCRIBE. It adds a condition for
Suppress-Notify-If-Match, and includes the entity-tag it
received in the previous NOTIFY.
10. The notifier evaluates the condition by matching its entity-tag
for the resource against the value of the Suppress-Notify-If-
Match header field. If the condition evaluates to true, the
notifier informs the subscriber that the notification was
blocked. This concludes the subscription.
The benefit of using conditional subscriptions in this example is in
the reduction of the number of NOTIFY requests the subscriber can
expect to receive. Each event notification that the subscriber has
already seen is blocked by the notifier. This example illustrates
only one use case for the mechanism; the same principles can be used
to optimize workflows related to other use cases of event
notification.
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4. Subscriber Behavior
This section augments the subscriber behavior defined in RFC3265 [4].
It first discusses general issues related to indicating support for
the mechanism (Section 4.1) and creating conditions in SUBSCRIBE
requests (Section 4.2); it then describes the workflows for the main
three use cases for making the subscription conditional.
4.1. Indicating Support for Entity Tags
The mechanism defined in this memo is backwards compatible with SIP
events [4] in that a notifier supporting this mechanism will insert a
SIP entity-tag in its NOTIFY requests, and a subscriber that
understands this mechanism will know how to use it in creating a
conditional request.
Unaware subscribers will simply ignore the entity-tag, make requests
without conditions and receive the default treatment from the
notifier.
However, to explicitly advertise the support for conditional
subscriptions, the subscriber MAY use the Supported header field in
advertising support for receiving entity tags in notifications.
Example:
Supported: subnot-etags
4.2. Generating Conditional SUBSCRIBEs
When creating a conditional SUBSCRIBE request, the subscriber MUST
include a conditional header field including an entity-tag to the
request. The condition is evaluated by comparing the entity-tag of
the subscribed resource with the entity-tag carried in the
conditional header field. If they match, the condition evaluates to
true.
Unlike the condition introduced for the SIP PUBLISH [1] method, these
conditions do not apply to the SUBSCRIBE request itself, but to the
resulting NOTIFY request. When true, the condition drives the
notifier to change its behavior with regards to sending the first
notification after the SUBSCRIBE.
There are two types of conditional header fields defined in this
specification:
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Suppress-Body-If-Match: if this condition evaluates to true, the
notifier is instructed to suppress (i.e., remove) the body of the
first NOTIFY request following the SUBSCRIBE. If false, the
notifier follows the default behavior.
Suppress-Notify-If-Match: if this condition evaluates to true, the
notifier is instructed to suppress (i.e., block) the entire first
NOTIFY request following the SUBSCRIBE, and instead send a 204 (No
Notification) response. If false, the notifier again follows the
default behavior.
The value of these header-fields is an entity-tag, which is an opaque
token that the subscriber simply copies from a previously received
NOTIFY request.
Examples:
Suppress-Body-If-Match: b4cf7
Suppress-Notify-If-Match: 628736
The conditional header field can also be wildcarded using the special
"*" entity-tag value. Such a condition always evaluates to true
regardless of the value of the current entity-tag for the resource.
Example:
Suppress-Notify-If-Match: *
4.3. Polling or Fetching Resource State
Polling with conditional notification allows a user agent to
efficiently poll resource state. This is accomplished using the
Suppress-Notify-If-Match condition:
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Subscriber Notifier
---------- --------
(1) SUBSCRIBE -------->
Supported: subnot-etags
Expires: 0
<-------- (2) 202
<-------- (3) NOTIFY
SIP-ETag: f2e45
(4) 200 -------->
... poll interval elapses
(5) SUBSCRIBE -------->
Supported: subnot-etags
Suppress-Notify-If-Match: f2e45
Expires: 0
<-------- (6) 204
Figure 2: Polling Resource State
1. The subscriber polls for resource state by sending a SUBSCRIBE
with zero expiry (expires immediately).
2. The notifier accepts the SUBSCRIBE with a 202 (Accepted)
response.
3. The notifier then immediately sends a first (and last) NOTIFY
request with the current resource state, and the current entity-
tag in the SIP-ETag header field.
4. The subsciber accepts the notification with a 200 (OK) response.
5. After some arbitrary poll interval, the subscriber sends another
SUBSCRIBE with a Suppress-Notify-If-Match header field that
includes the entity-tag received in the previous NOTIFY.
6. Since the resource state has not changed since the previous poll
occurred, the notifier sends a 204 (No Notification) response,
which concludes the poll.
Fetching resource state using conditional notification and the
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wildcard entity-tag allows two other types of operations as well:
Liveliness check: this allows a user agent to periodically check
whether a resource is still available. This is accomplished using
the Suppress-Notify-If-Match header field and the wildcard entity-
tag.
Meta-information query: this allows a user agent to query the latest
meta-information related to a resource. This is accomplished
using the Suppress-Body-If-Match header field and the wildcard
entity-tag.
4.4. Resuming a Subscription
Resuming a subscription means the ability to continue an earlier
subscription that either closed abruptly, or was explicitly
terminated. When resuming, the subscription is established without
transmitting the resource state. This is accomplished with
conditional notification and the Suppress-Body-If-Match header field:
Subscriber Notifier
---------- --------
(1) SUBSCRIBE -------->
Supported: subnot-etags
Suppress-Body-If-Match: ega23
Expires: 3600
<-------- (2) 202
<-------- (3) NOTIFY
SIP-ETag: ega23
Content-Length: 0
(4) 200 -------->
Figure 3: Resuming a Subscription
1. The subscriber attempts to resume an earlier subscription by
including a Suppress-Body-If-Match header field with the entity-
tag it last received.
2. The notifier accepts the subscription after proper authentication
and authorization, by sending a 202 (Accepted) (Accepted)
response.
3. The notifier then immediately sends an initial NOTIFY request
that now has no body. It also mirrors the current entity-tag of
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the resource in the SIP-ETag header field.
4. The subscriber accepts the NOTIFY and sends a 200 (OK) response.
Had the entity-tag not been valid any longer, the condition would
have evaluated to false, and the NOTIFY would have had a body
containing the latest resource state.
4.5. Refreshing a Subscription
To refresh a subscription using conditional notification, the
subscriber creates a subscription refresh before the subscription is
about to expire, and uses the Suppress-Notify-If-Match header field:
Subscriber Notifier
---------- --------
(1) SUBSCRIBE -------->
Supported: subnot-etags
Suppress-Notify-If-Match: aba91
Expires: 3600
<-------- (2) 204
Expires: 3600
Figure 4: Refreshing a Subscription
1. Before the subscription is about to expire, the subscriber sends
a SUBSCRIBE request that includes the Suppress-Notify-If-Match
header field with the latest entity-tag it has seen.
2. If the condition evaluates to true, the notifier sends a 204 (No
Notification) response sends no NOTIFY request. The Expires
header field of the 204 (No Notification) indicates the new
expiry time.
4.6. Terminating a Subscription
To terminate a subscription using conditional notification, the
subscriber creates a SUBSCRIBE request with a Suppress-Notify-If-
Match condition:
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Subscriber Notifier
---------- --------
(1) SUBSCRIBE -------->
Supported: subnot-etags
Suppress-Notify-If-Match: ega23
Expires: 0
<-------- (2) 204
Figure 5: Terminating a Subscription
1. The subscriber decides to terminate the subscription and sends a
SUBSCRIBE request with the Suppress-Notify-If-Match condition
with the entity-tag it has last seen.
2. If the condition evaluates to true, the notifier sends a 204 (No
Notification) response, which concludes the subscription, and the
subscriber can clear all state related to the subscription.
5. Notifier Behavior
This section augments the notifier behavior as specified in RFC3265
[4].
5.1. Generating Entity-tags
A notifier MUST generate entity tags for each resource it is
responsible for.
The views might correspond to different groups of users that have
varying levels of access rights to the resource state, or to
subscribers that have modified their subscription using event
notification filtering [11]. For example, in presence [6]
watchers may get different levels of accuracy in geolocation
information, based on the presentity's privacy settings.
An entity-tag is a token carried in the SIP-ETag header field, and it
is opaque to the client. The notifier is free to decide the means
for generating an entity-tag, except for the special "*" value. For
example, one possible method is to implement the entity-tag as a
simple counter, incrementing it by one for each generated
notification per resource.
An entity-tag is valid for as long as the resource state is valid.
The notifier MUST remember the entity-tag of a resource as long as
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the associated resource state is valid. The notifier MAY remember
the entity-tag longer than this, e.g., for implementing journaled
state differentials (Section 5.4).
The entity tag values used in publications are not necessarily shared
with the entity tag values used in subscriptions. This is because
there may not always be a one-to-one mapping between a publication
and a notification; there may be several sources to the event
composition process.
5.2. Suppressing NOTIFY Bodies
When a condition for suppressing a NOTIFY body is true, i.e., the
local entity-tag for the resource state and the subscriber provided
entity-tag in a Suppress-Body-If-Match header field match, the
notifier MUST suppress the body of the resulting NOTIFY request.
That is, the resulting NOTIFY contains no Content-Type header field,
the Content-Length is set to zero, and no payload is attached to the
message.
Suppressing the entity body of a NOTIFY does not change the current
entity-tag of the resource. Hence, the NOTIFY MUST contain a SIP-
Etag header field that contains the unchanged entity-tag of the event
state resource.
A Suppress-Body-If-Match header field that includes an entity-tag
with the value of "*" MUST always evaluate to true.
5.3. Suppressing NOTIFY Requests
When a condition in a SUBSCRIBE request to suppress a NOTIFY request
is true, i.e., the local entity-tag of the resource and the entity-
tag in a Suppress-Notify-If-Match header field of a SUBSCRIBE request
match, the notifier MUST suppress the resulting NOTIFY request, and
generate a 204 (No Notification) "No Notification" response.
Such a successful conditional SUBSCRIBE request MUST extend the
subscription expiry time.
Suppressing the entire NOTIFY has no effect on the entity-tag of the
resource. In other words, it remains unchanged.
A Suppress-Body-If-Match header field that includes an entity-tag
with the value of "*" MUST always evaluate to true.
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5.4. State Differentials
Some event packages may support a scheme where notifications contain
state differentials, or state deltas [4] instead of complete resource
state.
A notifier can optionally keep track of the state changes of a
resource, e.g., storing the changes in a journal. If a condition
fails, the notifier MAY send a state differential in the NOTIFY
rather than the full state of the event resource. This is only
possible if the event package and the subscriber both support a
payload format that has this capability.
When state differentials are sent, the SIP-ETag header field MUST
contain an entity-tag that corresponds to the full resource state.
5.5. List Subscriptions
OPEN ISSUE: What approach should we take in defining how conditional
notification works in RLSs? Seems there are roughly three different
approaches:
1. Treat meta-information as independent of the actual resource
state, don't apply conditional notification to meta-information
at all.
2. Treat everything as a single resource, and update the etag
whenever either meta or real info changes.
3. Have separate etags for meta and real information.
6. Protocol Element Definitions
This section describes the protocol extensions required for
conditional notification.
6.1. 204 (No Notification) Response Code
The 204 (No Notification) response code indicates that the request
was successful, but the notification associated with the request will
not be sent.
The response code is added to the "Success" production rule in the
SIP [3] message grammar.
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6.2. Suppress-Notify-If-Match Header Field
The Suppress-Notify-If-Match header field is added to the definition
of the "message-header" rule in the SIP [3] grammar. Its use is
described in Section 4 and Section 5.3.
This header field is allowed to appear in any request, but it's
behavior is only defined for the SUBSCRIBE request.
6.3. Suppress-Body-If-Match Header Field
The Suppress-Body-If-Match header field is added to the definition of
the "message-header" rule in the SIP [3] grammar. Its use is
described in Section 4 and Section 5.2.
This header field is allowed to appear in any request, but it's
behavior is only defined for the SUBSCRIBE request.
6.4. Grammar
This section defines the formal syntax for extensions described in
this memo in Augmented BNF (ABNF) [5]. The rules defined here
augment and reference the syntax defined in RFC3261 [3] and RFC3903
[1].
Success =/ "204" ; No Notification
; Success is defined in RFC3261.
message-header =/ Suppress-Body-If-Match
message-header =/ Suppress-Notify-If-Match
; message-header is defined in RFC3261.
Suppress-Body-If-Match = "Suppress-Body-If-Match" ":"
entity-tag / "*"
Suppress-Notify-If-Match = "Suppress-Notify-If-Match" ":"
entity-tag / "*"
; entity-tag is defined in RFC3903.
7. Open Issues and Todo
o The applicability of subnot-etags to RLS subscriptions should be
clarified. In particular, how does the entity-tag relate to RLMI
vs. the resource state?
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o Should add detailed examples of all of the different use cases for
conditional notification presented in this document.
8. IANA Considerations
This document registers a new SIP option-tag, a new response code and
two new header field names.
Note to IANA and the RFC editor: please replace all occurrences of
RFCXYZ in this section with the RFC number of this specification
upon publication.
8.1. "subnot-etags" Option Tag
This document registers a new SIP option tag. This option tag is
defined by the following information, which has been added to the
option-tags sub-registry under
http://www.iana.org/assignments/sip-parameters.
+--------------+----------------------------------------+-----------+
| Name | Description | Reference |
+--------------+----------------------------------------+-----------+
| subnot-etags | This option tag indicates support for | [RFCXYZ] |
| | entity-tags and conditional | |
| | notifications in SIP events. | |
+--------------+----------------------------------------+-----------+
8.2. 204 (No Notification) Response Code
This document registers a new response code. This response code is
defined by the following information, which has been added to the
methods and response-codes sub-registry under
http://www.iana.org/assignments/sip-parameters.
This information is to be added under "Successful 2xx" category.
+---------------------+-----------+
| Response Code | Reference |
+---------------------+-----------+
| 204 No Notification | [RFCXYZ] |
+---------------------+-----------+
8.3. Suppress-Body-If-Match Header Field
This document registers two new SIP header field names. These
headers are defined by the following information, which has been
added to the header fields sub-registry under
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http://www.iana.org/assignments/sip-parameters.
+------------------------+---------+-----------+
| Header Name | Compact | Reference |
+------------------------+---------+-----------+
| Suppress-Body-If-Match | | [RFCXYZ] |
+------------------------+---------+-----------+
8.4. Suppress-Notify-If-Match Header Field
This document registers two new SIP header field names. These
headers are defined by the following information, which has been
added to the header fields sub-registry under
http://www.iana.org/assignments/sip-parameters.
+--------------------------+---------+-----------+
| Header Name | Compact | Reference |
+--------------------------+---------+-----------+
| Suppress-Notify-If-Match | | [RFCXYZ] |
+--------------------------+---------+-----------+
9. Security Considerations
The security considerations for SIP event notification are
extensively discussed in RFC 3265 [4]. This specification introduces
an optimization to SIP event notification, which in itself does not
alter the security properties of the protocol.
10. Acknowledgments
The following people have contributed corrections and suggestions to
this document: Adam Roach, Sean Olson, Johnny Vrancken, Pekka Pessi,
Eva Leppanen, Krisztian Kiss, Peili Xu, Avshalom Houri, David
Viamonte and the SIP and SIMPLE working groups.
11. References
11.1. Normative References
[1] Niemi, A., "Session Initiation Protocol (SIP) Extension for
Event State Publication", RFC 3903, October 2004.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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[3] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[4] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[5] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
11.2. Informative References
[6] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", RFC 3856, August 2004.
[7] Mahy, R., "A Message Summary and Message Waiting Indication
Event Package for the Session Initiation Protocol (SIP)",
RFC 3842, August 2004.
[8] Rosenberg, J., "A Session Initiation Protocol (SIP) Event
Package for Registrations", RFC 3680, March 2004.
[9] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[10] Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-12 (work in progress), March 2007.
[11] Khartabil, H., Leppanen, E., Lonnfors, M., and J. Costa-
Requena, "Functional Description of Event Notification
Filtering", RFC 4660, September 2006.
Author's Address
Aki Niemi
Nokia
P.O. Box 407
NOKIA GROUP, FIN 00045
Finland
Phone: +358 50 389 1644
Email: aki.niemi@nokia.com
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