See Also
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.
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.