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

From: Werner Dittmann
Subject: Re: [Linphone-developers] patch to fix ZRTP sequence number handling
Date: Tue, 07 May 2013 10:48:34 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130307 Thunderbird/17.0.4

Am 07.05.2013 09:25, schrieb Guillaume Beraudo:
> 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.

The ZRTP protocol does not real use the sequence numbers, they are available 
the ZRTP packets look very similar to RTP packets. ZRTP would run even if all 
numbers are the same or non-existent. One may use the sequence numbers to get 
some idea
about network quality - UDP packets may arrive out of order or not at all. ZRTP 
its internal state transitions to control the protocol.

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

Groundwire's stack is built into the client and was developed independent of 
any other
ZRTP stack. Thus, if someone uses Groundwire there is not chance to avoid it.


> Cheers,
> Guillaume
> 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. 

Werner Dittmann    address@hidden
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