What is SDP (Session Description Protocol)?

In this article you can read about Session Description Protocol that is used between two networks for communication. If you are interested in this topic you can find more information and a video in the sections below.

SDP transports information on media streams, in multimedia sessions (exists for a certain duration of time) that includes e.g. session announcement and session invitation. It allows recipients to take part in SD (Session Description). It is primarily applied in inter-networks and also applied for describing conferences. The Session Description protocol does not send data itself, it is only used for the communication between end-points. In the picture below you can see that a VoIP phone and a softphone calls another VoIP phone that is transmitted by Ozeki Phone System XE and the call goes through an SDP channel (Figure 1).

Figure 1 - What is SDP?

1. communication during a session (session includes a sender, a receiver, and media stream)
2. transporting information to enable participation

1. session detailing (aim and name of session)
2. time (when it is active)
3. media

SDP messages contain several different sessions, time and media descriptions.

Session description values:

• v=(protocol version)
• o=(originator and session identifier)
• s=(session name)
• i=*(session information)
• e=*(email address)
• p=*(phone number)

• t= (time when the session is active)
• r=* (zero or more repeat times)

• m=(media name and transport address)
• c=*(connection information - optional if included at session-level)
• a=*(zero or more media attribute lines)

(* signs optional values)

With the help of a Session Description Protocol, you are able to make public and private sessions too. If you want to make a session private, you have to encrypt it.

The Session Description Protocol is supported by the Ozeki Phone System XE and it uses SDP in communication. Ozeki Phone System XE is an outstanding PBX telephone system that uses SDP to get information on data.

• What is RTP?
• What is RTCP?
• What is SRTP?
• What is H.323?
• What is SIP?