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

From: "Christian Hoene" <[email-masked]>
Date: Mon, 25 Jul 2011 10:33:27 -0400

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

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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