3.2 Sender Details

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The Sender side of this protocol MUST negotiate using SDP for a dynamic payload type binding for the redundancy data.

The redundancy data block MUST NOT have a distance greater than 3.

Distance is defined as the number of RTP packets succeeding the main block for which the redundancy block applies. For example, if RTP packet X contains main block A, and RTP packet X + n contains the redundancy block for main block A, that redundancy block has a distance of n. The maximum value of n MUST NOT exceed 3.

There MUST NOT be more than one redundancy block per RTP packet. At most two blocks are allowed per RTP packet: one main block and one redundancy block.

All redundant audio data from the Sender MUST be the same encoding (same codec) as the main audio block. This requirement deviates from [RFC2198] where secondary, tertiary, or other successive codecs are supported.

This means that the main audio block and redundant audio block MUST use the same codec.