################ WebRTC SDP ################ .. include:: ../links.ref .. include:: ../tags.ref .. include:: ../abbrs.ref ============ ========================== **Abstract** WebRTC SDP **Authors** Walter Fan **Status** WIP as draft **Category** LearningNote **Updated** |date| ============ ========================== .. contents:: :local: overview ============== An SDP session description includes the following: * Session name and purpose * Time(s) the session is active * The media comprising the session o Information needed to receive those media (addresses, ports, formats, etc.) An Offer/Answer Model with the SDP ======================================== * 每当需要 Offer/Answer 交换时，发起方都会通过调用 createOffer() API 创建 Offer。 * 然后，应用程序使用该 Offer 通过 setLocalDescription() API来设置其本地配置。offer 最终通过其首选的信令机制（例如WebSockets）发送到远程端；收到该 offer 后，远程方将使用 setRemoteDescription()API进行安置。 * 为了完成 Offer/Answer 交换，远程方使用 createAnswer() API生成适当的 answer，使用 setLocalDescription()`API应用该`answer，并将 answer 通过信令通道发送回发起方。 启动器获得该`answer`后，它将使用 setRemoteDescription() API进行安装，并且初始设置已完成。可以重复此过程以进行其他 Offer/Answer 交换。 参见 `RFC3264`_ RTP Profile for Audio and Video Conferences with Minimal Control =================================================================== 参见 `RFC3551 `_ SDP for ICE and DTLS ============================ 关于 DTLS extension to establish keys for SRTP, 请参见 `RFC5764 `_ SDP extension ============================ * DTLS fingerprint for SRTP (a=fingerprint) * RTP/RTCP Multiplexing (a=rtcp-mux) * RTCP Feedback support (a=rtcp-fb) * Host and server-reflexive candidate lines (a=candidate) * SRTP Setup framework parameters (a=setup) * RTCP attribute (a=rtcp) * RTP header extension indicating audio-levels from client to the mixer(a=extmap:1 * * urn:ietf:params:rtp-hdrext:ssrc-audio-level) SDP 的两个 Plan ======================= Plan B 和 Unified Plan .. code-block:: enum SdpSemantics { "plan-b", "unified-plan" }; partial dictionary RTCConfiguration { SdpSemantics sdpSemantics; } Negotiating Media Multiplexing Using SDP ============================================= 该扩展可以与SDP提供/应答机制一起使用，以协商使用单个传输（5元组）来发送和接收由多个SDP媒体描述所描述的媒体 5-tuple：client ip, client port, server ip, server port, protocol Allow an SDP 'group' attribute to contain an identification-tag that identifies a "m=" section with the port set to zero. It is to use a single transport(BUNDLE transport) for multiple media streams, defines a new SDP Grouping Framework [RFC5888] extension called 'BUNDLE'. 请参见 `RFC8843 `_ SDP Grouping Framework ============================================ The Session Description Protocol (SDP) Grouping Framework * Use of "group" and "mid" * Flow Identification (FID) - For each participant, the session is defined by a particular pair of destination transport addresses - But a single media instance maybe sent using more than one RTP session 请参见 `RFC5888 `_ Source-Specific Media Attributes in SDP ============================================ Defines a mechanism to describe RTP sources, identified by their synchronization source (SSRC) identifier, in SDP, to associate attributes with these sources, and to express relationships among individual sources. .. code-block:: a=ssrc: a=ssrc: : a=ssrc-group: ... 请参见 `RFC5576 `_ SDP examples ============================== 请参见 https://tools.ietf.org/html/draft-nandakumar-rtcweb-sdp-08 参见资料 ============================== * `SDP: Session Description Protocol `_ * `An Offer/Answer Model with the Session Description Protocol (SDP) `_ * `WebRTC 之 SDP `_ * `WebRTC 协议之 ROAP (RTCWeb Offer/Answer Protocol) `_