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Re: [Linphone-developers] patch to fix ZRTP sequence number handling

From: Guillaume Beraudo
Subject: Re: [Linphone-developers] patch to fix ZRTP sequence number handling
Date: Tue, 7 May 2013 09:25:37 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Hi Eli,

Thanks for the information.
I think we will integrate the patch, though it seems to me very strange to
receive chaotical sequence numbers.

Why are you using such a strange zrtp stack as Groundwire's?



On Tue, Apr 30, 2013 at 12:46:12PM -0400, Eli Burke wrote:
> Attached is a patch to oRTP that fixes incorrect handling of ZRTP sequence 
> numbers. We encountered a consistent error when connecting between Linphone 
> and Groundwire using ZRTP (note: compatibility with Groundwire requires my 
> previously submitted zrtp-hash patch). 
> Bug details: Linphone sends ZrtpHello and receives Groundwire's ZrtpHelloAck, 
> followed by ZrtpHello with a lower sequence number. This packet gets dropped 
> with the error "Discarding received out of order zrtp packet:..." and 
> Linphone never completes the ZRTP handshake. 
> Though you may conclude that Groundwire is misbehaving, it is in fact in 
> compliance with the RFC, which simply says:
> > The Sequence Number is a count that is incremented for each ZRTP
> >    packet sent.  The count is initialized to a random value.  This is
> >    useful in estimating ZRTP packet loss and also detecting when ZRTP
> >    packets arrive out of sequence.
> I have confirmed with Werner Dittmann (author of ZrtpCpp) that the sequence 
> number is only intended for diagnostic purposes and not for enforcing any 
> kind of packet ordering. 

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> Linphone-developers mailing list
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