Re: [AVT] gen-art review of draft-ietf-avt-rtp-atrac-family-16.txt

[Scott Brim <swb at employees.org>]

On 8/18/08 10:31 PM, actech allegedly wrote:
> Mr.Brim,
> 
> Thank you for your comments for 16th version of ATARC payload format.
> We agree with almost of your comments, and modified the draft
> according to that. However, for one issue (regarding on Fragment Number),
> we did not change the draft by the reason described below.
> 
> You can see the latest version of ATRAC payload format as
> draft-ietf-avt-rtp-atrac-family-17.txt.
> If you have further comments on the draft, please let us know.
> 
> Regards,
> 
> Jun

Thank you, Jun.  My response is below ...

> 
> ----------------------------------------------------
>> > 5.3.1 Usage of ATRAC Header Section
>> >
>> >  >    Fragment Number (FrgNo): 3 bits
>> >  >    In the event of data fragmentation, this value is one for the
>> >  >    first packet, and increases sequentially for the remaining
>> >  >    fragmented data packets. This value SHOULD be zero for an
>> >  >    unfragmented frame.
>> >
>> > Earlier it was said: "The ATRAC codec can handle very large frames.  As
>> > most IP networks have significantly smaller MTU sizes than the frame
>> > sizes ATRAC can handle ...".  If there can be such a significant
>> > difference -- and if you want to allow for larger frames in the future
>> > -- is there special handling for when this 3-bit counter rolls over
>> > (more than 7 fragments)?  If not, at least mention that you do not
>> > expect it to roll over -- or that you expect the receiver to be able to
>> > handle rollovers.
> 
> In ATRAC specification, it is described that supported bit-rate is
> up to 1.4Mbps. It corresponds to approximately 7500bytes/frame.
> So 3-bit counter is sufficient for expressioning Fragment Number,
> as far as the MTU size is 1500bytes.

I still make a friendly suggestion that you document that dependency,
because if there is an extension to the ATRAC specification in the
future to support a higher bit rate, this protocol might break.

Scott


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