[Freeswitch-users] SRTP media handling survey behaviour.

[Daniel Ivanov]

I wanted to implement a mixed mode of srtp and zrtp crypto capabilities
across our network and i was facing several issues. But succeeded
nonetheless. What kicked me in the balls hardest was rfc3713(taken from
memory) compliance of the UAs. Whenever i wanted to set SRTP to optional on
the devices sent both avp and savp lines along with the according keys in
the a=crypto lines in the sdp and the zrtp-hash too.
If for a reason i wanted to force ZRTP on the channel, i was supposed to
set sip_secure_media to false and that would disable srtp on the b-leg and
zrtp handshake would take place in p2p mode. I was using csipsimple(pjsip)
though and fs was just stripping the savp from the sdp and still passing
the a=crypto lines. It turned out greedy and still started talking srtp
instead of zrtp. I patched it myself to strip the a=crypto too if
sip_secure_media is false and it  worked like a german. I wanted to know if
anyone has observed how other UAs handle the srtp negotiation and if it's
worth proposing my patch as an improvement on the JIRA.
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