[xiph-rtp] My impressions about the discussion about codebook delivery.

[Ramón García]

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This is an attempt to summarize this discussion. I do not want to look
like an authority to say the final word. This is just the impression
that one has arrived after listening all of us.

After listening all this discussion, it looks like the best posible
method is to include in every RTP data packet an identifier of the
codebook needed for decoding this packet (16 bits or 32 bits) .  As
Aaron demonstrated, including off-line messages for changing codebooks
is not reliable, and could lead to wrong decoding. The overhead of a
codebook identifier is not large taking into account that the RTP
header already adds 128 bits.

For actual codebook delivery, HTTP is in my opinion the best option.
The session descriptor should have a pattern that tells how to
retrieve any codebook giving its identifier. This avoid shipping an
URL after the codebook changes. HTTP takes advantadge of the
transparent web proxies already used by most Internet providers.

One drawback of using HTTP is that it does not work with
unidirectional links. For these cases, a special type of RTP data
packets can be used. These packets can use marker bit of the RTP
header to be distingished from other packets. They should be sended
periodically by the server.

There are some issues that have not yet been discussed enough. Is it
necessary to provide dynamic changing of sampling rate? How should be
chained OGG files handled? I think that they should be handled like
playlists.

Ramon