Re: [AVT] WGLC on draft-ietf-avt-rtp-g711wb-03.txt

[Hitoshi Ohmuro <[e-mail]>]

Hi,

I discussed with some interested parties.

The number of parties who supported my proposal was limited.
It seems that most parties do not prefer even-size payload header or 
zero-padding to 1-octet one, because the significance of the processing 
problem is small, compared to the whole codec complexity.

I am ok with the current 1-octet payload header format.

I thank you for good discussions.

Regards,

Hitoshi Ohmuro


> Hi,
> 
> Sorry for my delayed comment.
> 
> I found an alignment problem for implementing the 1-octet payload header.
> 
> We are thinking of low-cost implementation of G.711.1 codec and RTP 
> stack on a DSP.
> Generally, a G.711.1 codec and an RTP stack are implemented as 
> independent functions.
> 
> An G.711.1 encoder generates even-size audio data, 40, 50, or 60 byte 
> data. RTP header always has 4-octet boundary.
> 
> If the payload header has a even-size, the RTP stack can combine the RTP 
> header, the payload header and the audio data easily, i.e. a DSP has 
> only to copy data word by word.
> 
> If the payload header has a odd-size, however, a 16-bit DSP has to copy 
> the audio data byte by byte using byte swapping like endian conversion. 
> This is due to 16-bit DSP memory architecture. This processing causes 
> much more overheads than even-size payload header.
> 
> I know that the communication protocol should not depend on a specific 
> hardware architecture.
> However, I know also that most of DSPs designed for speech signal 
> processing are optimized for 16-bit data.
> 
> I would like to propose that the payload header should be 2-octet and 
> the latter 1-octet is treated as a reserved byte which is default to zero.
> 
> This reserved byte might waste the bit rate, but we might be able to use 
> this byte for an optional purpose in the future, without 
> interoperability problems.
> 
> Please let me know your comments.
> 
> Regards,
> 
> Hitoshi Ohmuro
> 
> 
>> Hi,
>>
>>  
>>
>> This is to announce a working group last call on the RTP Payload 
>> Format for ITU-T Recommendation G.711.1
>>
>> Please send any final comments to the mailing list by May 27^th 2008.
>>  
>>
>> If no issues are raised, we will request the IESG consider the 
>> document for publication.
>>
>>  
>>
>>  
>>
>>  
>>
>> A New Internet-Draft is available from the on-line Internet-Drafts 
>> directories.
>>
>> This draft is a work item of the Audio/Video Transport Working Group 
>> of the IETF.
>>
>>  
>>
>>  
>>
>>             Title           : RTP Payload Format for ITU-T 
>> Recommendation G.711.1
>>
>>             Author(s)       : A. Sollaud
>>
>>             Filename        : draft-ietf-avt-rtp-g711wb-03.txt
>>
>>             Pages           : 15
>>
>>             Date            : 2008-04-28
>>
>>  
>>
>> This document specifies a Real-time Transport Protocol (RTP) payload 
>> format to be used for the International Telecommunication Union
>>
>> (ITU-T) G.711.1 audio codec.  Two media type registrations are also 
>> included.
>>
>>  
>>
>> A URL for this Internet-Draft is:
>>
>> http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-g711wb-03.txt
>>
>>  
>>
>> Internet-Drafts are also available by anonymous FTP at:
>>
>> ftp://ftp.ietf.org/internet-drafts/
>>
>>  
>>
>> Thanks
>>
>> Roni Even
>>
>>  
>>
>>
>> ------------------------------------------------------------------------
>>
>> _______________________________________________
>> Audio/Video Transport Working Group
>> [e-mail]
>> https://www.ietf.org/mailman/listinfo/avt

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