In the offer/answer model, Session Description Protocol (SDP) does not have a defined capability to negotiate one or more alternative transport protocols or attributes. For example, in the offer/answer model, SDP does not have a defined capability to negotiate the Real-time Transport Protocol (RTP) profiles. This SDP behavior has the following capability limitations:
deployment of new RTP profiles, such as Secure Real-time Transport Protocol (SRTP), or RTP, or Real-Time Transport Control Protocol (RTCP)-based feedback
negotiate use of different security keying mechanisms
To overcome the SDP limitations, the SDP capability negotiation feature implements a set of potential configurations indicating which combinations of capabilities and associated media components can be used for negotiating a session. During a session, the negotiation process implements the potential configurations as the input and provides the negotiated actual configurations as the output.
Note:
The SDP capability negotiation feature also supports SIP Direct Media. However, the SDP capability negotiation feature is not required because of SIP Direct Media.
You can implement the SDP capability negotiation feature to support SIP Direct Media and enhance the SIP SRTP capability in Avaya Aura® Communication Manager.
SIP SRTP enhancements in Communication Manager supporting SDP capability negotiation cause some memory overhead on the system. However, the memory overhead is insignificant and does not involve any bandwidth overhead.
