[Freeswitch-users] problems with freeswitch + zrtp in proxy-media mode

Eli Burke eburke at edge-net.net
Fri Feb 1 01:43:34 MSK 2013

I'm trying to use Freeswitch with an open source voip client called Linphone, but cannot manage to establish functioning ZRTP sessions. The problem *seems* to be related to the RTP stream's SSRC.  I'm trying to conclusively determine if the problem lies with Linphone, Freeswitch, or one of the underlying zrtp implementations (libzrtp and zrtpcpp).

Here's what I've determined so far:
1) ZRTP support is compiled and functioning. I can establish ZRTP sessions between two iPhones running Groundwire. 
2) linphone + ZRTP works correctly if I make a one legged call to a Freeswitch echo extension
3) linphone + ZRTP works correctly if I turn on bypass-media
4) linphone gets a CRC error when trying to verify the ZRTP packet on any two-legged call
5) disabling the CRC check results in a successful ZRTP session, but the audio is extremely garbled

Is Freeswitch modifying the ZRTP packets when running in proxy mode? If so, how is it that some clients are able to handle this situation?

Thanks for any suggestions,

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