3.4 Piggyback Notification in 200 OK Response Details

As a performance optimization, Session Initiation Protocol Extensions introduces a mechanism whereby the content of the first NOTIFY request that is normally sent in the SIP response to a SUBSCRIBE request can actually be carried in the SUBSCRIBE 200 OK response itself. This is referred to as piggybacking.

The benefit of this extension is in saving the traffic of the first NOTIFY request and its subsequent 200 OK response on the wire, reducing the total number of messages that must be processed as part of the usual login sequence for the client.

Note This extension can be used independently or in conjunction with the batched SUBSCRIBE mechanism defined previously.

This extension is optional. An implementation may support it.