[SR-Users] rtpengine - SRTP <> RTP missing a=crypto

Rhys Hanrahan rhys at nexusone.com.au
Thu Mar 3 16:20:26 CET 2022

Thanks guys! I was definitely just going off the default logging calls saying “new branch to xxx” in MANAGE_BRANCH. I am not intentionally creating separate branches in my config, so I guess it must be 1 branch! Good to know. Branches is another topic I still need to learn a lot more about.

Hopefully I can come up with the right config. I will keep working on it and let you know how I go.


From: sr-users <sr-users-bounces at lists.kamailio.org> on behalf of Matthias Urlichs <matthias at urlichs.de>
Reply to: "Kamailio (SER) - Users Mailing List" <sr-users at lists.kamailio.org>
Date: Friday, 4 March 2022 at 2:01 am
To: "sr-users at lists.kamailio.org" <sr-users at lists.kamailio.org>
Subject: Re: [SR-Users] rtpengine - SRTP <> RTP missing a=crypto

On 03.03.22 14:47, Rhys Hanrahan wrote:
Yes, from what I’ve seen in the logs there are multiple branches happening. One between Teams and Kamailio and one between Kamailio and Asterisk.

That's just one branch; the incoming call doesn't count. "Real" additional branches are created by calling functions like "append_branch".

You should definitely ensure (by adding appropriate logging calls) that "rtpengine_manage" is called exactly once per outgoing application/sdp message, with all requisite arguments(*). Anything else is a recipe for confusion. In my experience that's sufficient(**) to get it all working quite nicely.

(*) "trust-address replace-origin replace-session-connection", plus either RTP/AVP or RTP/SAVP

(**) unless the opposite end is broken. Right now, for instance, talking to Zoom Europe requires a heap of "SDES-no-RANDOM_CRYPTO_ALGORITHM" arguments, for both incoming and outgoing calls. Discovering that fix was decidedly nontrivial.


-- regards


-- Matthias Urlichs
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