Subject: [AVT] Comments on draft-perkins-avt-srtp-vbr-audio-02

From: Cullen Jennings <[email-masked]>
Date: Sun, 8 Nov 2009 13:31:47 +0900

On the advice to overhang the VAD by a random amount, I think I need  
more advice to implement this. Clearly if I put a random number from 0  
to 1 ms this won't work and if I pick a uniformly distributed random  
number between 0 and 1 day, it will more or less disable VAD. No  
complaints about the approach to this but I think I need more advice  
to be able to implement anything useful.

Is there other research that collaborates the spot-me stuff. I sort of  
wonder about it at times because the implications of it are that the  
success at picking the language when the system has all the  
unencrypted RTP, that the would be better than some of the results I  
see. I'm not saying I don't believe the spot-me stuff - I would just  
want to look at it much deeper before I decided and I was wondering  
what others had found. I often see results where the training data was  
too closely correlated with the the data used for the test results.

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From: Koen Vos <[email-masked]>
Date: Mon, 09 Nov 2009 04:01:30 -0800

If the average VAD overhang time is known by an interceptor, then it  
is still possible to estimate the average talk spurt length (and,  
thus, potentially the language). So the overhang statistics themselves  
should be randomly varied from call to call.

It would indeed be good to see more quantitative analysis, e.g. about:
- The size of the information leak
- How fast the leak shrinks by adding overhang
- How this leak compares to other leaks such as call duration and IP  
addresses.
It would make little sense to close a small leak if bigger ones are  
still wide open.

koen.

Quoting Cullen Jennings:
> more advice to implement this. Clearly if I put a random number from  
> 0 to 1 ms this won't work and if I pick a uniformly distributed  
> random number between 0 and 1 day, it will more or less disable VAD.  
> No complaints about the approach to this but I think I need more  
> advice to be able to implement anything useful.
>
> Is there other research that collaborates the spot-me stuff. I sort  
> of wonder about it at times because the implications of it are that  
> the success at picking the language when the system has all the  
> what others had found. I often see results where the training data  
> was too closely correlated with the the data used for the test  
> results._______________________________________________
> Audio/Video Transport Working Group
> [email-masked]
> https://www.ietf.org/mailman/listinfo/avt
>