I have asterisk connected to a gateway (sip trunk) to make outbound calls.
The problem is that when one extension is on a call, another extension calling to it doesn’t hear the call waiting sound (fast ringtone) but a normal ringback sound (as if the extension wasn’t on call).
To put it in simple words - if extension A and B are on a call, a call from extension C to either A or B results in extension C hearing a normal ringback sound instead of a call waiting sound.
What is the problem? where should I start looking?
A note: I have connected a SIP phone directly to the gateway (bypassed asterisk) and this way the SIP extension does hear the call waiting sound.