1. Introduction

The terminology about, and associations among, Real-time Transport Protocol (RTP) sources can be complex and somewhat opaque. This document describes a number of existing and proposed properties and relationships among RTP sources and defines common terminology for discussing protocol entities and their relationships.

2. Concepts

This section defines the key concepts and terminology used in RTP systems.

2.1. Media Chain

The media chain describes the complete path from media capture to media rendering:

Key Components

1. Physical Stimulus: The real-world audio or video that is captured
2. Media Capture: Device that converts physical stimulus to digital form
3. Raw Stream: Uncompressed digital media data
4. Media Source: Conceptual source of media content
5. Source Stream: Processed raw media ready for encoding
6. Media Encoder: Compresses source stream into encoded format
7. Encoded Stream: Compressed media data
8. Dependent Stream: Additional encoded data dependent on base stream
9. Media Packetizer: Packages encoded data into RTP packets
10. RTP Stream: Sequence of RTP packets with same SSRC
11. RTP-Based Redundancy: Mechanisms for adding redundancy
12. Redundancy RTP Stream: RTP stream carrying redundant data
13. RTP-Based Security: Security mechanisms (e.g., SRTP)
14. Secured RTP Stream: Encrypted/authenticated RTP stream
15. Media Transport: Network layer for RTP transmission
16. Media Transport Sender: Entity sending RTP over network
17. Sent RTP Stream: RTP stream as transmitted
18. Network Transport: Actual network path
19. Transported RTP Stream: RTP stream in transit
20. Media Transport Receiver: Entity receiving RTP from network
21. Received Secured RTP Stream: Received encrypted stream
22. RTP-Based Validation: Verification of received data
23. Received RTP Stream: Validated received stream
24. Received Redundancy RTP Stream: Received redundant data
25. RTP-Based Repair: Error correction mechanisms
26. Repaired RTP Stream: Stream after error correction
27. Media Depacketizer: Extracts encoded data from RTP packets
28. Received Encoded Stream: Encoded data after depacketization
29. Media Decoder: Decompresses encoded stream
30. Received Source Stream: Decompressed media data
31. Media Sink: Conceptual destination for media
32. Received Raw Stream: Uncompressed received media
33. Media Render: Presents media to user

2.2. Communication Entities

Endpoint

A device or application that sends and/or receives RTP streams.

RTP Session

An association among a set of participants communicating with RTP, defined by a pair of destination transport addresses (one for RTP, one for RTCP).

Participant

An entity that participates in an RTP session, identified by a unique RTCP CNAME.

Multimedia Session

A set of concurrent RTP sessions among a common group of participants, using one RTP session for each media type.

Communication Session

The complete set of RTP sessions and related signaling used for a communication between participants.