Subject: Re: [AVT] FEC draft

From: Magnus Westerlund <[email-masked]>
Date: Thu, 23 Oct 2003 14:27:26 +0200

Hi Adam,

Why not, it should simplify the processing somewhat. However I think 
this should be discussed openly, so I CC the AVT list in this reply. So 
if someone else has any comments about this, please respond.

Cheers

Magnus

Adam Li wrote:

> Hi Magnus,
> 
> I shuffle the fields around a little bit more (since we have them moved
> already). What do you think about the following format along the line
> you proposed? It have a even closer resemblance of the RTP header.
> 
>  0                   1                   2                   3
>  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> |E|L|P|X|  CC   |M| PT recovery |            SN base            |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> |                          TS recovery                          |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> |        length recovery        |             mask              |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> |              mask cont. (present only when L = 1)             |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> 
> Do you think this looks alright? Thanks a lot.
> 
> Adam
> 
> 
> 
>>-----Original Message-----
>>From: [email-masked] [mailto:[email-masked]] On Behalf Of
>>Magnus Westerlund
>>Sent: Wednesday, October 22, 2003 5:31 AM
>>To: Adam Li
>>Cc: [email-masked]
>>Subject: Re: [AVT] FEC draft
>>
>>Hi Adam,
>>
>>[chair hat of]
>>
>>I have actually thought this over and have a counter proposal that I
>>think is rather nice. First I would like to rearrange the header in
>>the
>>following way:
>>
>>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>|      SN base                  |        length recovery        |
>>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>|E|L|P|X|  CC   |M| PT recovery |             mask              |
>>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>|                          TS recovery                          |
>>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>
>>That way the 16 bits of fields matches the first 16 bits of the RTP
>>header. The sending part can simply XOR the headers of the packet as
>>is
>>and mask out the version bits.
>>
>>Secondly I would actually take the reserved bit and change it into a
>>"Long mask" indicator. When the L bit is set the header would then
>>actually look like this:
>>
>>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>|      SN base                  |        length recovery        |
>>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>|E|L|P|X|  CC   |M| PT recovery |             mask              |
>>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>|                         mask continued                        |
>>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>|                          TS recovery                          |
>>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>
>>That way one can allow for a 48 bit mask while still keeping the
>>number
>>of options low and keep the 32 bit alignment.
>>
>>What does you think about it?
>>
>>Cheers
>>
>>Magnus
>>
>>
-- 

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: [email-masked]

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