It's less complicated and unrelated to echo cancellation; you just tell the transmitting codec to always encode whatever audio you've given it, rather than detecting silence.
(Echo cancel is usually in the local audio path before data is passed to the codec. So the outbound codec would hear silence rather than an echo of inbound audio. At least that's my experience of working with PJ-SIP)
(Echo cancel is usually in the local audio path before data is passed to the codec. So the outbound codec would hear silence rather than an echo of inbound audio. At least that's my experience of working with PJ-SIP)