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3. Concepts of Inter-Relations

This section describes how different RTP streams and entities relate to each other.

3.1. Synchronization Context​

Mechanisms for synchronizing multiple RTP streams:

  • RTCP CNAME: Common identifier across streams requiring synchronization
  • Clock Source Signaling: Explicit signaling of timing relationships
  • RtcMediaStream: WebRTC mechanism for grouping synchronized streams
  • SDP Mechanisms: Session Description Protocol methods for indicating relationships

3.2. Key Relationship Patterns​

Simulcast​

Sending multiple encoded versions of the same source stream (e.g., different resolutions) in separate RTP streams, allowing receivers to select the most appropriate version.

Layered Multi-Stream​

Encoding media in hierarchical layers (base + enhancement layers) sent as separate RTP streams, where enhancement layers depend on base layers.

RTP Stream Duplication​

Sending identical copies of an RTP stream over different network paths for redundancy.

Redundancy Format​

Including redundant data within RTP packets to recover from packet loss.

RTP Retransmission​

Resending lost packets upon request from receiver.

Forward Error Correction (FEC)​

Adding error correction data that allows recovery without retransmission.

RTP Stream Separation​

Using different RTP streams for different purposes (e.g., separate streams for video and audio).

Multiple RTP Sessions​

Running multiple RTP sessions over a single media transport (e.g., using BUNDLE).

4. Mapping from Existing Terms

This section maps terminology from other specifications to the taxonomy defined in this document.

4.1. Telepresence Terms​

  • Audio Capture: Maps to Media Capture for audio
  • Capture Device: Maps to Media Capture
  • Capture Encoding: Maps to Media Encoder
  • Media Consumer: Maps to Media Sink
  • Media Provider: Maps to Media Source
  • Stream: Can map to various stream types depending on context

4.2. WebRTC Terms​

  • RtcMediaStream: Set of media sources sharing synchronization context
  • RtcMediaStreamTrack: Individual media source
  • Recording Device: Entity performing media capture

4.3. RTP Core Terms​

  • RTP Sender: RTP protocol part of media packetizer
  • RTP Receiver: RTP protocol part of media depacketizer
  • SSRC: Synchronization Source identifier for RTP stream

4.4. SVC Terms​

  • Single-Session Transmission (SST): All layers in one RTP session
  • Multi-Session Transmission (MST): Layers across multiple RTP sessions

4.5. Other Terms​

  • Media Description: SDP description of media
  • Media Stream: Can refer to various stream types
  • Multimedia Conference: Communication session with multiple participants
  • Multimedia Session: Set of concurrent RTP sessions
  • Multipoint Control Unit (MCU): Central mixing/switching entity
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