Microsoft Office Communications Server 2007, OCS 2007, is an enterprise real-time communications server, providing the infrastucture to allow instant messaging, presence, audio-video conferencing and web conferencing functionality.
Microsoft Office Communications Server uses the Session Initiation Protocol (SIP) for signaling along with the SIMPLE extensions to SIP for IM and presence. Media is transferred using RTP/SRTP. The Live Meeting client uses PSOM to download meeting content. The Communicator client also uses HTTPS to connect with the web components server to download address books, expand distribution lists, etc. By default, Office Communications Server encrypts all signaling and media traffic using SIP over TLS and SRTP. There is one exception to this - traffic between the Mediation Server and a basic media gateway is carried as SIP over TCP and RTP.