As a summary, my asterisk seems to be sending a 180 RINGING Message as a call progress indicator or something, and this is causing my sip endopoints to handle wrong the 486 BUSY HERE message when the called party phone is busy.
This is what I have:
PSTN Huwai Softswitch->Asterisk 1.2.1 -> SIP Endpoint (W7 Optics LMG)
The problem is that, when doing an outgoing call to the PSTN, the asterisk sends a RINGING back to the SIP Endpoint without even get yet any answer from the PSTN Softswitch… see this:
SIP Endpoint to Asterisk SIP/SDP Request: INVITE
Asterisk to SIP Endpoint SIP Status: 100 Trying
Asterisk to PSTN Softswitch SIP/SDP Request: INVITE
Asterisk to SIP Endpoint SIP Status: 180 Ringing
PSTN Softswitch to Asterisk SIP Status: 100 Trying
PSTN Softswitch to Asterisk SIP Status: 486 Busy Here
Asterisk to PSTN Softswitch SIP Request: ACK
Asterisk to SIP Endpoint SIP Status: 486 Busy here
SIP Endpoint to Asterisk SIP Request: ACK
If you see, at message 4 the Asterisk sends a 180 Ringing to the SIP Endpoint without even knowing if the call will be completed, busy, not found, service unavailable or whatever it can be. This is causing an early RINGING TONE at the SIP endpoint caller that doesn’t change when at the end the call was BUSY and then the caller gets confused because the phone rings and rings and the call is actually busy!
My sip endpoint is not able to understand the final 486 BUSY HERE (even that it acks the message) and then it just drop the call. I have checked with the vendor and this happen because having a ringing and then a busy on the same call represents a violation of the sip protocol. (not a problem on the endpoint)
I need to find a way to take out that early 180 RINGING, which i guess the asterisk uses as a “calling progress” attempt or something like that.
Please let me know what do you think!