[xiph-rtp] header caching and chaining

[Ralph Giles]

On Thu, Feb 10, 2005 at 10:10:35AM -0800, Aaron Colwell wrote:

> ok. I sort of lost track of what has happened here. Could someone provide a
> summary of the problem and solutions being proposed?

Oops. That's what I was trying to do when I started the thread.

> Here is what I've gotten from this discussion.
> 
> - There are concerns about collisions in the CRC

Yes. And we don't want to spend more per-packet bits on the ident.

> - The use of a unique ID is being proposed so that collisions are avoided,
>   but this brings up a problem of mapping the unique ID to the codebooks and
>   ident header.

It makes the mapping definition more pressing anyway.

> - There are some concerns that using a unique ID adversely effects the players
>   ability to cache codebooks and avoid retrieval when it isn't necessary.

Yes.

> If so here is a possible solution.
> 
> - Generate a unique ID for each chain. This could simply be the chain index 
>   (ie the Nth chain in the file will have a unique ID of N)
> 
> - The server publishes a base URL in the SDP that allows the client to retrieve
>   hashes and URLs for the codebook and ident header associated with each 
>   unique ID. The url for info associated with a particular unique ID is 
>   constructed by appending the unique ID to the base URL.

How many bits are you proposing for this id?

Using a regularized URL scheme also means clients can at least take 
advantage of HTTP caching mechanisms. That might be simpler than 
specifying some way to retrieve the hash separately.

I'd really like to see what the SDP would actually look like for 
this codebook transmission stuff. Can someone work up some examples? If 
we can somehow include a larger hash for the chain idents in the 
SDP, that would restore caching.

 -r