[SR-Users] mediaproxy-ng one-way audio (but not all the time)

[Richard Fuchs]

(Posting the follow-up of our off-list discussion for completeness)

On 08/22/13 10:36, Peter Dunkley wrote:

> I think (but I need to do more testing) the one way audio was related to
> early media and some issues with the media gateway I am using (which was
> generating the early media).  Removing the body from 18[03] responses
> (and converting 183 responses to 180) seems to have made the problem
> much better.
>
> However, I am still getting lots of "Error generating SRTP session keys"
> and occasional "Error generating SRTCP session keys" errors for every call.

The early media would indeed be responsible for the error messages you
see... SRTP uses asymmetric encryption keys, and the keys present in an
SDP body are to be used for the sending direction. IOW, with an offer
coming from an SRTP client which gets translated to a non-SRTP SDP,
mediaproxy can receive early media on those streams, but won't have an
SRTP encryption key for forwarding the media to the offerer, as the key
would only be sent in the answer SDP. Thus, SRTP (at least when used
through SDES) makes early media impossible.

However, that issue should resolve itself once the answer SDP goes
through, after which mediaproxy will have SRTP encryption keys for both
directions and the error should go away. Maybe there's a different issue
around? A full pcap including the RTP might be helpful.

cheers