Conferencing Protocols

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 following table shows the protocols that are used between conferencing components.

Table 1.   Conferencing Protocols

	Client	Focus	Focus Factory	Conferencing Server Factory	Conferencing server
Client	X	Session Initiation Protocol (SIP), Centralized Conferencing Control Protocol (C3P)	SIP, C3P	X	SIP, real-time transport protocol (RTP), Persistent Shared Object Model (PSOM) and so on
Focus	SIP, C3P	X	X	HTTPS, C3P	HTTPS, C3P
Focus Factory	SIP, C3P	X	X	X	X
Conferencing Server Factory	X	HTTPS, C3P	X	X	HTTPS, C3P
Conferencing Server	SIP, RTP, PSOM and so on	HTTPS, C3P	X	HTTPS, C3P	X

The following figure provides an overview of the protocols and the components that use them to communicate.

Figure 1. Office Communication Server 2007 R2 conferencing protocols and component relationships

Interfaces in the diagram identify a specific link, based on the transport and purpose, between two logical elements. The same protocol can be used in different ways over the various interfaces. For example, SIP/3CP is used to communicate C3P commands over SIP INFO messages and conference event package notifications over SIP SUBSCRIBE and NOTIFY messages.

Centralized Conferencing Control Protocol (C3P)

C3P is a conference manipulation protocol used by the Office Communications Server 2007 conferencing servers. C3P is used to modify the conference state. The channels over which C3P can be used in an Office Communications Server 2007 deployment are shown in Figure 1.

C3P has request/pending response/final response semantics similar to SIP. The following table lists C3P commands.

Table 2. C3P Commands

Conference Level
addConference
deleteConference
modifyConference
getConference
getMCU
modifyConferenceLock
modifyUsersMediaFilters

User Level
addUser
deleteUser
modifyUser
modifyUserRoles
setUserAccess

Scheduling
getAvailableMcuTypes
getConferencingCapabilities
getEncryptionKey
getConferences

Endpoint Level
modifyEndpointRole

Endpoint Media Level
addEndpointMedia
deleteEndpointMedia
modifyEndpointMedia

High Availability (HA)/Load Balancing
ping
getConference

PSOM

PSOM is the media protocol for data collaboration. PSOM uses Transport Layer Security (TLS) as the underlying transport. Conferencing clients can use PSOM to establish media channels with the Web Conferencing Server to negotiate or transfer media.

RTP/RTCP

RTP/RTCP is the standard protocol for the transport of real-time data, including audio and video.

SIP/SDP

Session Initiation Protocol (SIP) is the industry standard protocol described in IETF RFC 3261 that defines a standard way for session setup, termination, and media negotiation between two parties. It is widely used for Voice over IP (VoIP) call signaling.

Session Description Protocol (SDP) is the industry standard protocol described in IETF RFC 4566 that defines a standard way to convey media details, transport addresses, and other session description metadata to the participants when initiating multimedia teleconferences, Voice over IP calls, streaming video, or other sessions.

Signaling and Control Protocol

This section describes the protocols supported by the various server components and the functionality supported by each of those protocols. Clients and servers use signaling and control protocols for session setup and conference management. For each media in a conference or an audio/video call, different media protocols are used.

SIP, as specified in RFC 3261, is used for session setup and termination in Office Communications Server 2007. SIP messages use Transmission Control Protocol (TCP) or TLS as the underlying transport layer for client-to-server communications and mutual TLS (MTLS) for server-to-server communications. Conferences and call control are established within the context of existing SIP sessions using C3P protocol. C3P commands are sent using SIP INFO messages. A separate SUBSCRIBE/NOTIFY dialog is used to subscribe to conference packages, state change notifications, and the conference participant list.

Media Protocols

The Web Conferencing Server uses PSOM as the media protocol for data collaboration. PSOM uses TLS as the underlying transport. As the client for the Web Conferencing Server, Live Meeting functionality also relies on PSOM.

RTP and RTCP are used to transport audio/video and desktop sharing data. By default, Office Communications Server 2007 uses secure real-time transport protocol (SRTP) and secure real-time transport control protocol (SRTCP) to secure and encrypt both media types. RTP/RTCP can use either TCP or User Datagram Protocol (UDP) as the underlying transport for audio/video, but will use only TCP for desktop sharing.

See Also

Concepts

Communication Protocols for Office Communication Server 2007 R2