Implement dual-stream through the SIP protocol

This article original from the http://blog.csdn.net/voipmaker reprint indicate the source.

Dual-stream is the concept in video conferencing. It generally means that the client can display two video streams at the same time, one is the main video (main), and the other is usually the content sharing (slides ), it is also called share content. Content is usually screen, PPT, document, and other content.

The SIP protocol implements dual-stream. The SDP contains two video media tags. One is main, which indicates the main video stream and the other is slides, which indicates the second stream. The SDP format is as follows:

v=0 o=Alice 330742730 33077831 IN IP4 172.101.72.11 s=lecture c=IN 172.101.72.11 t=0 0 m=video 52986 RTP/AVP 31 a=rtpmap:31 H261/9000 a=content:slides m=video 53134 RTP/AVP 31 a=rtpmap:31 H261/9000 a=content:main

Use a = content to differentiate two video streams. Each video stream is a separate RTP Port.

The two-stream protocol of SIP must be jointly controlled by the SIP and bfcp protocols. bfcp is used for permission application. That is, when the client wants to share documents and other content, it must initiate a bfcp floor request to other clients, after the request passes negotiation, the client adds the SDP information of the second video stream through the re-invite of the SIP to enable the second video stream.

RFC for bfcp: http://tools.ietf.org/html/rfc4582

Implement dual-stream through the SIP protocol