New SIP RFCs Supported by WebSphere 7 (Join, Replace and Update)

Support was added in WAS 7.0 for the following three RFCs: 3911 (Join Header) and 3891 (Replaces Header). These are very similar RFCs but are used for different purposes. Join is used to join an existing dialog and replaces is used to replace an old dialog with a new dialog.

From abstract of RFC 3911:

This document defines a new header for use with SIP multi-party applications and call control. The Join header is used to logically join an existing SIP dialog with a new SIP dialog. This primitive can be used to enable a variety of features, for example: "Barge-In", answering-machine-style "Message Screening" and "Call Center Monitoring".

From abstract of RFC 3891:

The Replaces header is used to logically replace an existing SIP dialog with a new SIP dialog. This primitive can be used to enable a variety of features, for example: Attended Transfer and Call Pickup.

In terms of RFC 3911, the Join header contains information used to match an existing SIP dialog (call-id, to-tag, and from-tag) to the new dialog being created. From the JSR 116 perspective, the join header can be used to add a new dialog/SIP session to an existing SIP Application session in much the same way that an encoded URI is used. This is achieved by setting the call-id, to-tag and from-tag in the join header of the INVITE to match that of an existing dialog.

In terms of RFC 3991, the Replaces header contains information used to match and replace an existing SIP dialog (call-id, to-tag, and from-tag) to the new dialog being created. From the JSR 116 perspective, the join header can be used to replace an existing SIP session associated with a SIP Application Session with a new dialog/session. This is achieved by setting the call-id, to-tag and from-tag in the replaces header of the INVITE to match that of an existing dialog. Note that it is up to the application to send a BYE on the original dialog, the container will not take care of this for you so that from the JSR perspective there really is not much difference between Join and Replaces.

RFC 3311 support was also added to WAS 7. This RFC defines the use of the Update method. From abstract of RFC 3311:

UPDATE allows a client to update parameters of a session (such as the set of media streams and their codecs) but has no impact on the state of a dialog. In that sense, it is like a re-INVITE, but unlike re-INVITE, it can be sent before the initial INVITE has been completed. This makes it very useful for updating session parameters within early dialogs.