Communication Manager supports and enhances the SIP SRTP capability by using SDP capability negotiation. SDP Capability Negotiation is a mechanism that enables SDP to provide limited support to indicate system capabilities and the associated potential configurations and negotiate the use of the potential configurations as actual configurations. SDP Capability Negotiation provides a general SDP Capability Negotiation framework that is backward compatible with the existing SDP and defines specifically how to provide attributes and transport protocols as capabilities and negotiates them using the framework. The SIP SRTP enhancements in Communication Manager enable the following:

• Support the SIP User Agent (UA) to provide both SRTP and non-SRTP capabilities in a single SDP Capability Negotiation.

• Support Direct Media functionality in Communication Manager by eliminating the requirement of NULL INVITE at the Callee leg during the initial call setup.

• Simplify the SIP SRTP call flow.

• Enable the SIP endpoints and Communication Manager to provide complete encryption capabilities to each other and increases the call shuffling capability of Communication Manager.

SIP signaling with SDP capability negotiation is backward compatible with the existing SRTP implementation and also with SIP implementations not supporting SRTP.