Concept and structure of SDP protocol

Next we will introduce the SDP protocol. So what is the specific role of this agreement? What does it mean? Session Description Protocol (SDP) provides multimedia session description 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. The SDP protocol 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 transmission protocols, including session notification protocol SAP), Session Initiation Protocol SIP), real-time stream protocol RTSP), MIME extension protocol e-mail 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. The session notification protocol SAP is used for sending SDP messages. It 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 be sent by email or WWW World Wide Web.

SDP text information includes:

Session name and intent;

Session duration;

Media that constitutes a session;

The information address of the Receiving media ).

Protocol Structure

The information of the SDP protocol is text information, which adopts the ISO 10646 character set in the UTF-8 coding.

The SDP session is described as follows: the optional fields 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 contained in all media)
B = * bandwidth information)

One or more times are described as follows ):

Z = * Time Zone adjustment)
K = * encryption key)
A = * 0 or multiple session attribute rows)
Description of 0 or multiple media sets)

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)