2.2 Message Syntax

  • Article

The structure and syntax of RTPRAD are defined within RTP Payload for Redundant Audio Data [RFC2198]. This protocol does not cover all audio data redundancy. It is limited to in-band audio communication data. This protocol MUST NOT be used to carry audio data redundancy for audio data such as in-band DTMF tones. For more information about in-band DTMF tones, see [RFC4733].

The deviation from [RFC2198] is as follows:

  • Section 2 of [RFC2198] provides for one or more redundant audio blocks for each RTP payload. However, this protocol description allows for only one redundant block for every RTP payload. Therefore, each RTP payload MUST NOT contain more than two blocks total: one redundancy block and one primary block.

  • Section 2 of [RFC2198] describes the mechanism for including the redundancy information in the RTP packet header. However, RTPRAD does not support redundant information in the RTP header. The RTP header MUST NOT contain redundant information. RTPRAD MUST be made part of a dynamic RTP payload type and negotiate as such during SDP negotiation.

  • While section 2 of [RFC2198] allows for static typing of payload types, systems interoperating with an implementation of this protocol MUST negotiate for dynamic redundancy payload type using SDP or redundancy is not enabled.