SIP Update Method

1 Call Flows
2 Configuration

The UPDATE method allows a User Agent Client (UAC) the ability to update the parameters of a session, such as the SDP and session timers. The Update Method has no impact on the state of a dialog. In that sense, the Update Method is like a re-INVITE, except that it can be sent before the initial INVITE has been completed. This makes it very useful for updating session parameters within early dialogs.

The UPDATE method allows greater control over a SIP session including, but not limited to, the following parameters

SDP (for example, to set the media on hold during early media)
Session timers (for example, to adjust call duration in a prepaid application)

The IMG 2020 supports the following for SIP Update Method:

An UPDATE request that is received before or after the initial INVITE transaction is completed and when a dialog exists (early or confirmed), in accordance with RFC 3261.
The validation of an SDP contained in an UPDATE follows the existing restrictions of the offer/answer model (RFC 3264).
The IMG 2020 will reject an Update Method request that is meant as a FAX re-INVITE. Although it is possible, the RFC does not recommend the use of the Update method in this fashion.
Follows recommendations of RFC 3311 The SIP Initiation Protocol (SIP) Update Method.

Call Flows

IMG 2020 handles a User Agent Server (UAS) UPDATE transaction while in a UAS INVITE transaction.

IMG 2020 initiates a UAC UPDATE transaction while in a UAS INVITE transaction

IMG 2020 handles a UAS UPDATE transaction while in a UAC INVITE transaction

IMG 2020 initiates a UAC UPDATE transaction while in a UAC INVITE transaction

IMG 2020 handles a UAS UPDATE transaction while in answered state

IMG 2020 initiates a UAC UPDATE transaction while in answered state

Configuration

The SIP Update Method is by default enabled and cannot be modified.

Dialogic Integrated Media Gateways