Network Working Group G. Camarillo
Request for Comments: 5362 Ericsson
Category: Standards Track October 2008
The Session Initiation Protocol (SIP) Pending Additions Event Package
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document defines the SIP Pending Additions event package. This
event package is used by SIP relays to inform user agents about the
consent-related status of the entries to be added to a resource list.
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Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................3
3. Overview of Operation ...........................................3
4. XML Schema Definition ...........................................3
5. Pending Additions Event Package Definition ......................5
5.1. Event Package Name .........................................5
5.1.1. Event Package Parameters ............................5
5.1.2. SUBSCRIBE Bodies ....................................5
5.1.3. Subscription Duration ...............................5
5.1.4. NOTIFY Bodies .......................................5
5.1.5. Notifier Processing of SUBSCRIBE Requests ...........6
5.1.6. Notifier Generation of NOTIFY Requests ..............6
5.1.7. Subscriber Processing of NOTIFY Requests ............6
5.1.8. Handling of Forked Requests .........................7
5.1.9. Rate of Notifications ...............................7
5.1.10. State Agents .......................................7
5.1.11. Example ............................................7
6. Partial Notifications ...........................................8
6.1. Generation of Partial Notifications ........................8
6.2. Processing of Partial Notifications ........................9
6.3. XML Schema for Partial Notifications .......................9
6.4. Examples ..................................................11
7. IANA Considerations ............................................11
7.1. SIP Event Package Registration ............................11
7.2. URN Sub-Namespace Registration: consent-status ............12
7.3. XML Schema Registration: consent-status ...................12
7.4. XML Schema Registration: resource-lists ...................13
7.5. MIME Type Registration:
application/resource-lists-diff+xml .......................13
8. Security Considerations ........................................14
9. Acknowledgments ................................................14
10. Normative References ..........................................14
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1. Introduction
The framework for consent-based communications in SIP [RFC5360]
identifies the need for users manipulating the translation logic at a
relay (e.g., adding a new recipient) to be informed about the
consent-related status of the recipients of a given translation.
That is, the user manipulating the translation logic needs to know
which recipients have given the relay permission to send them SIP
requests.
This document defines a SIP event package whereby user agents can
subscribe to the consent-related state of the resources that are
being added to a resource list that defines a translation.
2. Terminology
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 [RFC2119].
Relay: Any SIP server, be it a proxy, B2BUA (Back-to-Back User
Agent), or some hybrid, that receives a request, translates its
Request-URI into one or more next-hop URIs (i.e., recipient URIs),
and delivers the request to those URIs.
3. Overview of Operation
A user agent subscribes to a relay using the Pending Additions event
package. NOTIFY requests within this event package can carry an XML
document in the "application/resource-lists+xml" format [RFC4826] or
in the "application/resource-lists-diff+xml" format, which is based
on XML patch operations [RFC5261].
A document in the "application/resource-lists+xml" format provides
the user agent with the whole list of resources being added to a
resource list along with the consent-related status of those
resources. A document in the "application/resource-lists-diff+xml"
format provides the user agent with the changes the list of resources
being added has experimented with since the last notification sent to
the user agent.
4. XML Schema Definition
This section defines the element, which provides
consent-related information about a resource to be added to a relay's
translation logic.
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A consent-status document is an XML document that MUST be well-formed
and SHOULD be valid. Consent-status documents MUST be based on XML
1.0 and MUST be encoded using UTF-8. This specification makes use of
XML namespaces for identifying consent-status documents. The
namespace URI for elements defined for this purpose is a URN, using
the namespace identifier 'ietf'. This URN is:
urn:ietf:params:xml:ns:consent-status
The element can take on the following values:
Pending: the relay has received a request to add a resource to its
translation logic and will ask for permission to do so.
Waiting: the relay has requested permission to add the resource to
its translation logic but has not gotten any answer from the
resource yet.
Error: the relay has requested permission to add the resource to its
translation logic and has received an error response (e.g., a SIP
error response to the MESSAGE request sent to request permission).
That is, the permission document requesting permission could not
be delivered to the resource.
Denied: the resource has denied the relay permission to add the
resource to the relay's translation logic.
Granted: the resource has granted the relay permission to add the
resource to the relay's translation logic.
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Section 5.1.11 contains an example of an "application/resource-
lists+xml" document that carries consent-related state information
using elements.
5. Pending Additions Event Package Definition
This section provides the details for defining a SIP [RFC3261] event
notification package, as specified by [RFC3265]. Support for this
section (i.e., Section 5) is REQUIRED for implementations of this
specification. Support for partial notifications is optional, but if
a subscriber signals support for partial notifications, Section 6
MUST be implemented.
5.1. Event Package Name
The name of this event package is "consent-pending-additions". This
package name is carried in the Event and Allow-Events header, as
defined in [RFC3265].
5.1.1. Event Package Parameters
This package does not define any event package parameters.
5.1.2. SUBSCRIBE Bodies
A SUBSCRIBE for Pending Additions events MAY contain a body. This
body would serve the purpose of filtering the subscription. Filter
documents are not specified in this document and, at the time of
writing, they are expected to be the subject of future
standardization activity.
A SUBSCRIBE for the Pending Additions event package MAY be sent
without a body. This implies that the default session policy
filtering policy has been requested. The default policy is that
notifications are generated every time there is any change in the
state of a resource in the list.
5.1.3. Subscription Duration
The default expiration time for a subscription is one hour (3600
seconds).
5.1.4. NOTIFY Bodies
In this event package, the body of the notifications contains a
resource list document. This document describes the resources being
added as recipients to a translation operation. All subscribers and
notifiers MUST support the "application/resource-lists+xml" data
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format [RFC4826] and its extension to carry consent-related state
information, which is specified in Section 4. The SUBSCRIBE request
MAY contain an Accept header field. If no such header field is
present, it has a default value of "application/resource-lists+xml".
If the header field is present, it MUST include
"application/resource-lists+xml", and MAY include any other types
capable of representing consent-related state.
Additionally, all subscribers and notifiers SHOULD support the
"application/resource-lists-diff+xml" format. Section 6 discusses
the usage of the Pending Additions event package with this format.
5.1.5. Notifier Processing of SUBSCRIBE Requests
The state of the resources to be added to a relay's translation logic
can reveal sensitive information. Therefore, all subscriptions
SHOULD be authenticated and then authorized before approval.
Authorization policy is at the discretion of the administrator.
5.1.6. Notifier Generation of NOTIFY Requests
A notifier for the Pending Additions event package SHOULD include the
element, which is defined in Section 4. The
element MUST be positioned as an instance of the
element within the element.
Notifications SHOULD be generated for the Pending Additions package
whenever there is a change in the consent-related state of a
resource. When a resource moves to the error, denied, or granted
states, and once a NOTIFY request is sent, the resource is removed
from further notifications.
5.1.7. Subscriber Processing of NOTIFY Requests
As stated in Section 3, a document in the "application/resource-
lists+xml" format provides the subscriber with the whole list of
resources being added to a resource list along with the consent-
related status of those resources. On receiving a NOTIFY request
with such a document, the subscriber SHOULD update its local
information about the resources being added to the resource list with
the information in the document. NOTIFY requests contain full state.
The subscriber does not need to perform any type of information
aggregation. Section 6 discusses the use of the Pending Additions
event package with partial notifications.
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5.1.8. Handling of Forked Requests
The state of a given resource list is normally handled by a server
and stored in a repository. Therefore, there is usually a single
place where the resource-list state is resident. This implies that a
subscription for this information is readily handled by a single
element with access to this repository. There is, therefore, no
compelling need for a subscription to pending additions information
to fork. As a result, a subscriber MUST NOT create multiple dialogs
as a result of a single subscription request. The required
processing to guarantee that only a single dialog is established is
described in Section 4.4.9 of [RFC3265].
5.1.9. Rate of Notifications
For reasons of congestion control, it is important that the rate of
notifications not become excessive. As a result, it is RECOMMENDED
that the server does not generate notifications for a single
subscriber at a rate faster than once every 5 seconds.
5.1.10. State Agents
State agents have no role in the handling of this package.
5.1.11. Example
The following is an example of an "application/resource-lists+xml"
document that carries consent-related state information using
elements:
Bill Doe
pending
Joe Smith
pending
Nancy Gross
granted
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6. Partial Notifications
The lists of resources reported by this event package may contain
many resources. When the "application/resource-lists+xml" format is
used and there is a change in the consent-related status of a
resource, the server generates a notification with the whole list.
Generating large notifications to report small changes does not meet
the efficiency requirements of some bandwidth-constrained
environments. The partial notifications mechanism specified in this
section is a more efficient way to report changes in the status of
resources.
Subscribers signal support for partial notifications by including the
"application/resource-lists-diff+xml" format in the Accept header
field of the SUBSCRIBE requests they generate. If a client
subscribing to the Pending Additions event package generates an
Accept header field that includes the MIME type
"application/resource-lists-diff+xml", the server has the option of
returning documents in this format (instead of in the
"application/resource-lists+xml" format).
6.1. Generation of Partial Notifications
Once a subscription is accepted and installed, the server MUST
deliver full state in its first notification. To report full state,
the server uses the regular format for resource lists. Consequently,
the server MUST set the Content-Type header field to the value
'application/resource-lists+xml'.
In order to deliver a partial notification, the server MUST set the
Content-Type header field to the value 'application/resource-lists-
diff+xml'. When the server generates a partial notification, the
server SHOULD only include the information that has changed since the
previous notification. It is up to the server's local policy to
determine what is considered as a change to the previous state.
The server MUST construct partial notifications according to the
following logic: all information that has been added to the document
is listed inside elements, all information that has been
removed from the document is listed inside elements, and all
information that has been changed is listed under elements.
The server MUST NOT send a new NOTIFY request with a partial
notification until it has received a final response from the
subscriber for the previous one or the previous NOTIFY request has
timed out.
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When the server receives a SUBSCRIBE request (refresh or termination)
within the associated subscription, it SHOULD send a NOTIFY request
containing the full document using the 'application/resource-
lists+xml' content type.
If the server has used a content type other than
'application/resource-lists+xml' in notifications within the existing
subscription and changes to deliver partial notifications, the server
MUST deliver full state using the 'application/resource-lists+xml'
content type before generating its first partial notification.
6.2. Processing of Partial Notifications
When a subscriber receives the first notification containing full
state in a 'application/resource-lists+xml' MIME body, the subscriber
MUST store the received full document as its local copy.
When the subscriber receives a subsequent notification, the
subscriber MUST modify its locally stored information according to
the following logic:
o If the notification carries an %'application/resource-lists+xml'
document, the subscriber MUST replace its local copy of the
document with the document received in notification.
o If the notification carries an 'application/resource-lists-
diff+xml' document, the subscriber MUST apply the changes
indicated in the received 'application/resource-lists-diff+xml'
document to its local copy of the full document.
If a subscriber encounters a processing error while processing an
'application/resource-lists-diff+xml' encoded document, the
subscriber SHOULD renew its subscription. A subscriber can fall back
to normal operations by not including the 'application/resource-
lists-diff+xml' format in a new SUBSCRIBE request.
If the server changes the content type used in notifications within
the existing subscription, the subscriber MUST discard all the
previously received information and process the new content as
specified for that content type.
6.3. XML Schema for Partial Notifications
This is the XML schema for the "application/resource-lists-diff+xml"
data format. The "urn:ietf:params:xml:schema:xml-patch-ops" schema
is defined in [RFC5261].
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6.4. Examples
Section 5.1.11 contains an example of an 'application/resource-
lists+xml' document, which carries full state. The following is an
'application/resource-lists-diff+xml' partial update document:
granted
The following is the resulting 'application/resource-lists+xml'
document after applying the partial update:
Bill Doe
granted
Joe Smith
pending
Nancy Gross
granted
7. IANA Considerations
There are five IANA considerations associated with this
specification.
7.1. SIP Event Package Registration
This specification registers a SIP event package per the procedures
in [RFC3265].
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Package name: consent-pending-additions
Type: package
Contact: Gonzalo Camarillo
Published Specification: RFC 5362.
7.2. URN Sub-Namespace Registration: consent-status
This section registers a new XML namespace per the procedures in
[RFC3688].
URI: The URI for this namespace is
urn:ietf:params:xml:ns:consent-status
Registrant Contact: IETF SIPPING working group ,
Gonzalo Camarillo
XML:
Pending Additions Extension Namespace
Namespace for Consent-related Status Information Extension
urn:ietf:params:xml:ns:consent-status
See RFC 5362
.
7.3. XML Schema Registration: consent-status
This section registers an XML schema per the procedures in [RFC3688].
URI: urn:ietf:params:xml:schema:consent-status
Registrant Contact: IETF SIPPING working group ,
Gonzalo Camarillo
The XML for this schema can be found in Section 4.
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7.4. XML Schema Registration: resource-lists
This section registers an XML schema per the procedures in [RFC3688].
This XML schema is an extension to the XML schema (whose ID is
resource-list) defined in [RFC4826]. The IANA has added a row in the
XML schema registry with the following values:
ID: resource-lists-diff
URI: urn:ietf:params:xml:schema:resource-lists-diff
Filename: resource-lists-diff
Reference [RFC5362]
Registrant Contact: IETF SIPPING working group ,
Gonzalo Camarillo
The XML for this schema can be found in Section 6.3.
7.5. MIME Type Registration: application/resource-lists-diff+xml
This section registers the 'application/resource-lists-diff+xml' MIME
type.
MIME media type name: application
MIME subtype name: resource-lists-diff+xml
Mandatory parameters: none
Optional parameters: Same as charset parameter application/xml as
specified in [RFC3023].
Encoding considerations: Same as encoding considerations of
application/xml as specified in [RFC3023].
Security considerations: See Section 10 of [RFC3023] and Section 7 of
[RFC4826].
Interoperability considerations: none
Published specification: RFC 5362
Applications that use this media type: This document type has been
defined to support partial notifications in subscriptions to
resource lists.
Additional Information:
Magic number: none
File extension: .rld
Macintosh file type code: "TEXT"
Personal and email address for further information: Gonzalo
Camarillo
Intended usage: COMMON
Author/Change controller: The IETF
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8. Security Considerations
"A Framework for Consent-Based Communications in the Session
Initiation Protocol (SIP)" [RFC5360] discusses security-related
issues that are related to this specification.
Subscriptions to the Pending Additions event package can reveal
sensitive information. For this reason, it is RECOMMENDED that
relays use strong means for authentication and information
confidentiality. Additionally, attackers may attempt to modify the
contents of the notifications sent by a relay to its subscribers.
Consequently, it is RECOMMENDED that relays use a strong means for
information integrity protection.
It is RECOMMENDED that relays authenticate subscribers using the
normal SIP authentication mechanisms, such as Digest, as defined in
[RFC3261].
The mechanism used for conveying information to subscribers SHOULD
ensure the integrity and confidentially of the information. In order
to achieve these, an end-to-end SIP encryption mechanism, such as
S/MIME, as described in [RFC3261], SHOULD be used.
If strong end-to-end security means (such as above) is not available,
it is RECOMMENDED that hop-by-hop security based on TLS and SIPS
URIs, as described in [RFC3261], is used.
9. Acknowledgments
Jonathan Rosenberg provided useful ideas on this document. Ben
Campbell and Mary Barnes performed a thorough review of this
document. Jari Urpalainen helped improve the partial notifications
mechanism.
10. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3261] 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.
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[RFC3265] Roach, A.B., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC4826] Rosenberg, J., "Extensible Markup Language (XML) Formats
for Representing Resource Lists", RFC 4826, May 2007.
[RFC5261] Urpalainen, J., "An Extensible Markup Language (XML) Patch
Operations Framework Utilizing XML Path Language (XPath)
Selectors", RFC 5261, September 2008.
[RFC5360] Rosenberg, J., Camarillo, G., and D. Willis, "A Framework
for Consent-Based Communications in the Session Initiation
Protocol (SIP)", RFC 5360, October 2008.
Author's Address
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
EMail: Gonzalo.Camarillo@ericsson.com
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Full Copyright Statement
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contained in BCP 78, and except as set forth therein, the authors
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RFC, FYI, BCP