Re: [codec] [payload] Padding in draft-ietf-codec-opus-07?

Jean-Marc Valin <jmvalin@jmvalin.ca> Mon, 25 July 2011 21:12 UTC

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Date: Mon, 25 Jul 2011 17:12:09 -0400
From: Jean-Marc Valin <jmvalin@jmvalin.ca>
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Subject: Re: [codec] [payload] Padding in draft-ietf-codec-opus-07?
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On 11-07-25 01:24 PM, Stephen Botzko wrote:
> I think RTP padding should be sufficient.

Well, it is possible for Opus to be transmitted in real-time over
something other than RTP. Also, even for RTP, there's the issue that the
padding bit is transmitted in the clear, which would impose padding even
frames that would not otherwise need padding.

	Jean-Marc

> Regards,
> Stephen
> 
> Sent from my Verizon Wireless Device
> 
> Christian Hoene <hoene@uni-tuebingen.de> wrote:
> 
>> Hello,
>>
>> I am wondering about a padding feature in draft-ietf-codec-opus-07. It
>> allows you to extend the frame size by filling it up with zeros.
>>
>> I just spoke with the Tim, Jean-Marc and Gregory about this feature. As far
>> as I understood, this feature is required at transcoding gateways to enforce
>> a stream of packets having a constant size (while using UDP). Otherwise,
>> attackers could potentially follow the conversation by observing packet
>> sizes. 
>>
>> To my understanding, padding is a feature that can be easily skipped from
>> the codec specification. It violates the layering principle and is intended
>> only for a very specific use cases. On the other side, constant sized frames
>> can be easily supported by keeping the codec parameters fixed.
>>
>> With best regards,
>>
>> Christian Hoene
>>
>>
>>
>> ----------------------------------------------------------------------------
>> -----
>> Dr.-Ing. Christian Hoene, University of Tübingen, Computer Science, Chair of
>> Communication Networks, Research Group Interactive Communication Systems
>> (ICS)
>> Sand 13, 72076 Tübingen, Germany, Tel +49 7071 2970532,
>> www.net.uni-tuebingen.de
>>
>>
>>
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