This application describes how Session Description Protocol (SDP)
preconditions signaling can be enhanced to support lead role negotiation,
precondition capability exchange, premature precondition attempts and
concatenated preconditions processing. The application describes the use
of send and receive tags in an SDP message for a given media line. In a
given message, a success or failure tag may be associated with a send or
receive tag in addition to an optional or mandatory condition indicator
tag. A lead role indicator may also be associated with a send or receive
tag to indicate a desired preference with regard to the sender or
receiver taking the lead role. These additions lead to a greater chance
of successful session set-up completion, reduce the number of signaling
exchanges in general, and enable precondition attempts to be started
earlier and to be executed in parallel.