If I understand correctly, Asterisk 14 introduced support for some new SRTP ciphers (including some 256 bit ones), previously only two 128 bit ciphers were supported.
Using Asterisk 14, I was able to make a call from a softphone (Groundwire) with a 256 bit cipher suite on SRTP, which is great.
However, I don’t see any way to specify with PJSIP (or chan sip) , the cipher suite which should be used when Asterisk calls the endpoint/phone.
So I believe this means Asterisk would always use 128 bit SRTP to call the phone. Then, if you have 256 bit only ciphers allowed on the phone, the call fails.
Perhaps this is just not documented, or may not be implemented yet. Anyone have a thought?