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Protocols Used in Office Communications Server 2007

Microsoft Office Communications Server 2007 and Microsoft Office Communications Server 2007 R2 will reach end of support on January 9, 2018. To stay supported, you will need to upgrade. For more information, see Resources to help you upgrade your Office 2007 servers and clients.

The Unified Communications vision that is embodied in Office Communications Server 2007 is built on SIP (Session Initiation Protocol), an industry standard, application layer signaling protocol for starting, controlling, and ending communication sessions in an IP-based network. SIP is formally described in the IETF (Internet Engineering Task Force) reference specification RFC 3261. By using SIP, one user can explicitly invite another to join a conversation or multimedia session. A SIP session begins when the second user accepts a SIP INVITE request.

In Office Communications Server 2007, SIP is used for IM, conferencing, presence subscriptions, video, and VoIP, providing a common user experience across all these communication modes. Signaling for phone calls coming from the PSTN is converted to SIP by the media (PSTN) gateway.

Although SIP sessions can include the sharing of real-time media, SIP itself does not handle the actual media data, such as audio, video, and application sharing. In practical terms, this separation means that SIP and various media protocols can evolve independently.

Other protocols that are used in Office Communications Server 2007 include the following:

  • HTTP (Hypertext Transfer Protocol). A standard Internet protocol that in Office Communications Server 2007 is used for communication between the Focus and conferencing servers, downloading Address Book Server updates to clients, and downloading meeting content to users.

  • C3P (Centralized Conference Control Protocol). A custom protocol for communicating conference creation and control commands from clients to Office Communications Server 2007. C3P commands are carried as XML in SIP SERVICE or INFO messages. CP3 commands are also carried over HTTPS to all conferencing servers.

  • PSOM (Persistent Shared Object Model). A custom protocol for transporting Web conferencing content.

  • SRTP (Secure Real-time Transport Protocol). An IETF standard protocol that is used in Office Communications Server 2007 for securely transporting audio and video content to various media devices. It is based on the RTP that defines a packet format for carrying audio and video over IP networks.

  • RTCP (Real-Time Control Protocol). An IETF standard protocol used in conjunction with RTP and SRTP to convey information about the signal quality of an audio/video conferencing session to various media devices.