SDP: Session Description Protocol)

 

The Session Description Protocol (SDP) provides multimedia session descriptions for session notifications, session invitations, and other forms of multimedia session initialization.

The session directory is used to assist with multimedia conference announcements and send relevant settings for session participants. SDP is used to transmit this information to the receiving end. SDP is completely a session description format-it is not a Transport Protocol-it only uses different appropriate transport protocols, including session notification protocol (SAP) and Session Initiation Protocol (SIP), real-time stream protocol (RTSP), mime extension protocol email and Hypertext Transfer Protocol (HTTP ).

SDP is designed to be universal. It can be applied to a wide range of network environments and applications, not just multicast session directories, but SDP does not support negotiation of session content or media encoding.

In the Internet multicast Backbone Network (mbone), the Session Directory tool is used to notify multimedia meetings and send the meeting address and the meeting-specific tool information required by the participants, which is completed by SDP. After the session is connected, the SDP sends enough information to the session participant. Session notification protocol (SAP) is used to send SDP messages, which periodically multicast notification packets to known multicast addresses and ports. This information is a UDP packet, which contains the sap protocol header and text payload ). Here, the text payload refers to the SDP Session Description. In addition, the information can also be sent via email or WWW (World Wide Web.

SDP text information includes:

• Session name and intent;
• Session duration;
• Media that constitutes a session;
• Information about the received media (addresses, etc ).

Protocol Structure

SDP information is text information, using the ISO 10646 character set in the UTF-8 encoding. The SDP session is described as follows: (an optional field marked with the * symbol ):

• V = (Protocol Version)
• O = (owner/creator and session identifier)
• S = (Session name)
• I = * (session information)
• U = * (URI description)
• E = * (email address)
• P = * (phone number)
• C = * (connection information-this field is not required if it is included in all media)
• B = * (bandwidth information)

One or more time descriptions (as shown below ):

• Z = * (Time Zone adjustment)
• K = * (encryption key)
• A = * (0 or multiple session attribute rows)
• 0 or more media descriptions (as shown below)

Time description

• T = (Session Activity time)
• R = * (0 or repeated times)

Media description

• M = (media name and transfer address)
• I = * (media title)
• C = * (connection information-this field is optional if it is included in the Session Layer)
• B = * (bandwidth information)
• K = * (encryption key)
• A = * (0 or multiple session attribute rows)

Organization Source: SDP is defined by IETF (http://www.ietf.org/) in RFC 2327.

Link: http://www.javvin.com/protocol/rfc2327.133: Session Description Protocol.