【RFC simulcast SDP】 https://datatracker.ietf.org/doc/html/draft-ietf-mmusic-sdp-simulcast-13

• 原文 Using Simulcast in SDP and RTP Sessions
  draft-ietf-mmusic-sdp-simulcast-13
• SDP 不仅关系到链接建立
• 而且是信令设计的初衷
• 快速过一遍 simulcast 的 SDP 设计文档，掌握基础知识，后面遇到有个印象，遇到问题再回头查阅。

simulcast

• send multiple
  differently encoded versions of the same media source in different
  RTP streams. This is called simulcast.

SDP

• This document describes how
  to accomplish simulcast in RTP and how to signal it in SDP.
• The
  described solution uses an RTP/RTCP identification method to identify
  RTP streams belonging to the same media source, and makes an
  extension to SDP to relate those RTP streams as being different
  simulcast formats of that media source