While Session Initiation Protocol (SIP) is still the primary control protocol used by Office Communications Server 2007 R2, Web Conferencing Server, A/V Conferencing Server, and their subcomponents, they also employ other protocols to set up and modify conferences and to set up and break down media streams between different elements in the Office Communications Server2007 R2 network. The following protocols are employed by Office Communications Server 2007 R2:
Session Initiation Protocol (SIP).The industry standard
protocol described in IETF RFC 3261 that defines a standard for
session setup, termination, and media negotiation between two
parties. It is widely used for Voice over IP (VoIP) call signaling.
Web Access to ensure efficient client-server interaction, while
keeping the Web user interface (UI) responsive.
Centralized Conferencing Control Protocol (C3P).Used to
encode Conferencing Control commands in Office Communications
HTTPS.The set of rules for exchanging files (that is, text,
graphic images, sound, video, and other multimedia files) on the
World Wide Web. Relative to the Transmission Control Protocol
(TCP)/Internet Protocol (IP) suite of protocols, the basis for
information exchange on the Internet, HTTP is an application-layer
protocol. HTTPS is the HTTP protocol over Secure Sockets Layer
(SSL)/Transport Layer Security (TLS).
Interactive Connectivity Establishment (ICE).Used to provide
media connectivity across firewalls and Network Address Translation
(NAT) devices, thereby enabling audio/video anywhere.
Persistent Shared Object Model (PSOM).A proprietary protocol
for the transport of real-time data, including audio and video.
PSOM uses TCP or TLS as the underlying transport.
Remote Desktop Protocol (RDP).The Microsoft protocol that is
used in Office Communications Server 2007 R2 for desktop sharing.
This is the protocol that is used for Microsoft Remote Desktop
Real-time transport protocol/real-time control protocol
(RTP/RTCP).The industry standard protocol for the transport of
real-time data, including audio and video.
Session Description Protocol (SDP).Used to negotiate
capabilities between SIP endpoints during call initiation.
Secure real-time transport protocol/secure real-time control
protocol (SRTP/SRTCP).Encrypted versions of RTP/RTCP.
Scale secure real-time transport protocol (SSRTP).Scale
secure RTP/RTCP, used for efficient media sessions for multi-point
Simple Traversal of UDP through NAT (STUN).Used by endpoints
to determine the public IP addresses allocated to them by the NAT
Transport Layer Security (TLS).Used to encrypt SIP or HTTP
trafficin addition to server authentication.
Third Party Control Protocol (TPCP).Used for Outside Voice
Traversal Using Relay NAT (TURN).A protocol for allocating a
public IP address and port on a globally reachable server for the
purpose of relaying media from one endpoint to another.
For detailed specifications for Office Communications Server
protocols, including several of those listed in this topic, see
“Microsoft Office Protocol Documents” at