Re: [AVT] draft-kerr-avt-vorbis-rtp-04

Hi,

On 16 Jan 2005, at 18:42, Phil Kerr wrote:
> Colin Perkins wrote:
>> On 4 Jan 2005, at 15:54, Phil Kerr wrote:
>>> An -04 update of the Vorbis-RTP draft was submitted a few days ago.
>>>
>>> http://www.ietf.org/internet-drafts/draft-kerr-avt-vorbis-rtp-04.txt
>>>
>>> Major changes include:
>>>
>>> Removal of RTCP-based transport for configuration headers, replaced 
>>> with in-band transport.
>>> Inclusion of a CRC32 header field used to tie the stream to the 
>>> associated decoding codebook.
>>
>>
>> This is an interesting idea. How is the CRC32 calculated? What is the 
>> chance of collision, and how would that be resolved?
>
> The CRC32 is calculated from the codebook header itself.

Actually, I meant what is the CRC algorithm, not which data is it 
calculated using?

> The chance of collision should be quite low, MD5 would be a lot safer 
> in this regard but it does add quite a lot of overhead to each packet. 
>  There may need to be an additional identifier, possibly a host id 
> which ties the CRC32 value to the host, which is sent via SDP to 
> reduce the chance of collision further.

Host identifiers are difficult to pick too, so I'm not sure that'd help.

Can you expand on why the CRC was chosen, and why a table-indexing to 
onto a list of URLs wouldn't work?

Cheers,
Colin

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