[Freeswitch-users] scratch sound at beginning of SRTP call

[Maarten Ureel]

Hello

I am running a setup where calls from the outside are not encrypted with SRTP (from our SIP trunk), and locally (between phone & FS) they are.
I put in the vars.xml:
<X-PRE-PROCESS cmd="set" data="rtp_secure_media=optional:AES_CM_128_HMAC_SHA1_80"/>

This all works fine, however with one disturbing fact; when you pick up the call you  hear a loud "static" noise. I think this is the phase where the suite is negotiated, because it's the same as when we force SRTP on FreeSWITCH and disable it in the phone (but then the call fails afterwards of course).

So what I would need to accomplish:

  *   Either the phone needs to negotiate the SRTP before it's answered (is that even possible?), e.g. during ring
  *   If the negotiation has to take place after answering, that it doesn't generate this loud noise in the meantime.

It could also be due to the used phone (Yealink, T42G and T46G). With RTX phones we didn't have this issue yet but I only tested it with one device. But if someone has some pointers on what causes this...

Thanks for your input!

Regards
Maarten

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