SIPPING Working Group G. Camarillo
Internet-Draft Ericsson
Expires: August 6, 2004 February 6, 2004
Requirements and Framework for Session Initiation Protocol (SIP)
Exploder Invocation
draft-camarillo-sipping-exploders-02.txt
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Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document describes the need for SIP exploders and provides
requirements for their invocation. Additionaly, it defines a
framework which includes all the SIP extensions needed to meet these
requirements.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1 Carrying URI Lists in SIP . . . . . . . . . . . . . . . . . . 5
4.2 Managing Ad-Hoc URI Lists . . . . . . . . . . . . . . . . . . 5
4.3 Transaction State Information . . . . . . . . . . . . . . . . 5
4.4 Multiple REFER Targets . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . 6
Normative References . . . . . . . . . . . . . . . . . . . . . 6
Informational References . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
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1. Introduction
Some applications require that, at a given moment, a SIP UA performs
a similar transaction with a number of remote UAs. For example, an
instant messaging application that needs to send a particular message
(e.g., "Hello folks") to n receivers needs to send n MESSAGE
requests; one to each receiver.
When the transacton that needs to be repeated consists of a large
request, or the number of recipients is high, or both, the access
network of the UA needs to carry a considerable amount of traffic.
Completing all the transactions on a low-bandwidth access would
require a long time. This is unacceptable for a number of
applications.
A solution to this problem consists of introducing exploders in the
network. The task of an exploder is to receive a request from a UA
and send a number of similar requests to a number of destinations.
Once the requests are sent, the exploder needs to inform the UA about
their status. Effectively, the exploder behaves as a B2BUA.
Note that resource lists, as described in [2], already use SIP
exploders for SUBSCRIBE transactions. Still, the set of destinations
needs to be preconfigured using out-of-band mechanisms (e.g., XCAP).
The Advanced Instant Messaging Requirements for SIP [3] also
mentions the need for exploders for MESSAGE transactions:
"REQ-GROUP-3: It MUST be possible for a user to send to an ad-hoc
group, where the identities of the recipients are carried in the
message itself."
The remainder of this document provides requirements to invoke
exploders in an efficient manner and a framework that meets these
requirements.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [1] and indicate requirement levels for
compliant implementations.
3. Requirements
This section contains the requirements:
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1. The invocation mechanism MUST allow the invoker to provide a
list of destination URIs to the exploder. This URI list MAY
consist of one or more URIs.
2. It MUST be possible to send URI list "deltas" to update the list
of URIs handled by the exploder.
3. The invocation mechanism MUST NOT be request specific.
4. The invocation mechanism SHOULD NOT require more than one RTT.
5. An exploder MAY provide services beyond request explosion. That
is, exploders can be modelled as application servers. For
example, an exploder handling INVITE requests may behave as a
conference server and perform media mixing for all the
participants.
6. The interpretation of the meaning of the URI list sent by the
invoker MUST be at the discretion of the application to which
the list is sent.
7. It MUST be possible for the invoker to find out about the result
of the operations performed by the application with the URI
list. An invoker may, for instance, be interested in the status
of the transactions initiated by the exploder.
8. It MUST be possible for the application that makes use of a list
of URIs to convey the list of URIs to any recipients of messages
created by the application from that list. OPEN ISSUE: do we
really need this requirement?
9. Exploders MUST NOT perform any request explosion without
authenticating the invoker.
10. The UA MUST be able to provide credentials to the exploder so
that the exploder can use them to prove to the destinations that
it is sending requests on behalf of the UA.
4. Framework
Although Section 3 contains specific requirements for SIP exploders,
this framework is not restricted to application servers that only
provide request explosion services. We also deal with application
servers that provide a particular service that includes a request
explosion (e.g., a conference server that INVITEs several
participants which are chosen by a user agent).
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We need to use several SIP extensions to meet the requirements in
Section 3. We list these extensions in the following sections and
explain which role they play within the framework.
4.1 Carrying URI Lists in SIP
User agents can send a list of URIs to an application server using
the list SIP and SIPS URI parameter defined in
(draft-camarillo-sipping-uri-list-01). The user agent adds a list
parameter to the Request-URI of the SIP request sent to the
application server. This parameter contains a pointer to a URI list,
which can be carried in the SIP request itself or can be stored in an
external server (e.g., an http URI pointing to an XCAP resource
list). The way the application server interprets the URI list
received in the request is service specific.
4.2 Managing Ad-Hoc URI Lists
An application server that receives a request with a URI list (or a
pointer to it) creates a so called ad-hoc list, whose lifetime
depends on the service provided by the server. Services that involve
ad-hoc lists that are valid for a period of time need to allow user
agents to modify these lists.
A user agent can manage ad-hoc lists at a server in two ways, as
described in (draft-camarillo-sipping-adhoc-management-00): using SIP
or using an external means (e.g., XCAP).
User agents using SIP to manage ad-hoc lists send a new SIP request
with a pointer to a new list that will substitute the old list.
User agents using an external means to manage ad-hoc lists need to
obtain from the server a URI that allows them to manipulate the list
(e.g., an http URI pointing to an XCAP resource list). The server
provides such a URI in an Associated-List-Manipulation header field
in the response to the request that created the ad-hoc list.
4.3 Transaction State Information
User agents may be interested in the results of the message explosion
at the application server. That is, user agents may want to know the
result of the transactions that the application server initiated
towards the URIs in the URI list provided by the user agent. The
transaction state event package defined in
(draft-camarillo-sipping-transac-package-00) provides this
information to the user agent subscribing to this package.
Still, in order to subscribe to the transaction state event package,
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the user agent needs a URI to subscribe to. The application server
provides such a URI in an Associated-Transactions-State header field
in the response to the request that triggered the new transactions,
as defined in (draft-camarillo-sipping-transac-package-00).
4.4 Multiple REFER Targets
Building REFER requests with multiple REFER targets requires special
considerations, as described in
(draft-camarillo-sipping-multiple-refer-00). The Refer-To header
field carries a pointer to a URI list, and the NOTIFIES carry
transaction state information using the transaction state event
package. User agents may use bodies whose disposition type is
template to describe the messages to be sent by the application
server.
A conferencing application is an example of an application that may
use REFERs with multiple REFER targets. A user agent may send a REFER
to the conferencing server so that the server BYEs a set of users.
5. Security Considerations
Requirements related to security are considered in Section 3.
TBD: this section should be expanded considerably.
6. Acknowledges
Duncan Mills and Miguel A. Garcia-Martin supported the idea of 1 to n
MESSAGEs.
Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
Informational References
[2] Roach, A., Rosenberg, J. and B. Campbell, "A Session Initiation
Protocol (SIP) Event Notification Extension for Resource
Lists", draft-ietf-simple-event-list-04 (work in progress), June
2003.
[3] Rosenberg, J., "Advanced Instant Messaging Requirements for the
Session Initiation Protocol (SIP)",
draft-rosenberg-simple-messaging-requirements-00 (work in
progress), December 2002.
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Author's Address
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
EMail: Gonzalo.Camarillo@ericsson.com
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