Real-Time Protocols


Protocols in this table enable transmission of real-time data between multimedia endpoints. The Real-Time Transport Protocol (RTP) is a set of network transport functions suitable for applications transmitting real-time data, such as audio and video, from one multimedia endpoint to one or more multimedia endpoints. During a Communications Server conference that includes audio, video, desktop, or application-sharing data, the protocol client connects to the Audio/Video/Application Sharing Conferencing Server, and media is exchanged through the RTP. An RTP session is established using SIP/SDP, which manages the negotiation for the RTP session, including defining the transport, payload, and security parameters. The RTP and its associated control protocol, Real-Time Transport Control Protocol (RTCP), are formally described in [RFC3550]. In addition, [RFC3551] defines the set of payload-type codes and payload formats for audio and video.

Protocol name


Short name

Exchange Unified Messaging Session Description Protocol Extension

Describes the extensions to SDP that negotiate and establish audio calls between protocol servers and unified messaging servers to play or record voice messages and to manage the unified messaging mailbox by using touch-tone commands.


RTP Payload for DTMF Digits, Telephony Tones, and Telephony Signals Extensions

Describes the payload format for transmitting dual-tone multi-frequency (DTMF) signaling, tone signals, and telephony events in RTP packets.


RTP Payload Format for H.264 Video Streams Extensions

Describes the payload format for encapsulating an H.264 video stream.


Real-time Transport Protocol (RTP) Extensions

Extends the standard Real-Time Transport Protocol (RTP) [RFC3550]. The extensions define features such as dominant speaker notification, enhanced host security, bandwidth estimation, and lost packet notification.


RTP Payload for Redundant Audio Data Extensions

Describes a payload format that contains redundant audio encoding to help reduce packet loss. If a packet is dropped, redundant data is carried in a subsequent packet so that the lost data can be reconstructed.


RTP for Application Sharing Payload Format Extensions

Extends the Real-time Transport Protocol (RTP) Extensions protocol (as described in [MS-RTP]) with a set of Microsoft® proprietary extensions to the base Real-Time Transport Protocol (RTP) [RFC3550], to transfer the application-sharing payload that is encoded in the graphics format described by the Remote Desktop Protocol: Basic Connectivity and Graphics Remoting Specification [MS-RDPBCGR].


RTP Payload Format for RT Video Streams Extensions

Describes the RTP payload format for encapsulating an RTVideo (real-time video) stream.


Session Description Protocol (SDP) Version 2.0 Protocol Extensions

Describes the extensions to SDP that enable protocol clients to negotiate advanced media session capabilities with Communications Server.


Secure Real-time Transport Protocol (SRTP) Extensions

Describes a framework for encryption and message authentication for both the RTP and RTCP streams. The protocol client and protocol server use SRTP when exchanging RTP traffic in either direction.


Scale Secure Real-time Transport Protocol (SSRTP) Extensions

Describes the extensions to SRTP that improve performance in scenarios where the same RTP payload is distributed to a large number of recipients. This includes cryptographic and message authentication processes that differ from the Secure Real-time Transport Protocol (SRTP) Extensions, as described in [MS-SRTP].