We have an Asterisk 1.4 server with a multi-FXO port Sangoma telephony card installed that is receiving inbound calls from our customer’s on-site equipment. Our customer’s technician informed us that he can provide only two options to indicate call hang up – “dial tone on disconnect, or a standard hard disconnect”. We’ve tried several different Asterisk settings and neither option is being recognized, so the line stays open until a timeout is hit.
When we tried “standard hard disconnect” we saw the voltage sit at 51 volts while waiting for a call, drop to 7-9 volts when the call connected, and then remain at 7 after a hang up. No polarity reversal was noted either.
We’re currently receiving an audibly recognizable dial tone, but Asterisk isn’t detecting it.
You need to find a PSTN provider who can provide proper PABX lines, with disconnect supervision.
I’m not a Dahdi expert, but I don’t remember any suggestions that Asterisk can use dial tone detect for clearing. In any case, you would be vulnerable to this being spoofed by the the caller, and even more likely, the callee.
The low voltage state on the line is created by the Asterisk being off hook.
[quote=“david55”]You need to find a PSTN provider who can provide proper PABX lines, with disconnect supervision.
I’m not a Dahdi expert, but I don’t remember any suggestions that Asterisk can use dial tone detect for clearing. In any case, you would be vulnerable to this being spoofed by the the caller, and even more likely, the callee.
The low voltage state on the line is created by the Asterisk being off hook.[/quote]
[quote]By default, asterisk listens for a busy tone or a a dial tone on the line to detect if the line got hung up.
These tones are different in different countries, duration and tones might differ a little between carriers.[/quote]
The voltage measurements related to what our customer’s technician referred to as a “standard hard disconnect” were intended to show that we can’t detect a voltage drop at disconnect using this methodology. We also thought that maybe he was referring to polarity reversal, but that wasn’t detected either.
As I said, I’m not a dahdi expert. The problem with using dialtone for disconnect supervision is that you may get dialtone from the far end if they want you to send DTMF digits; there is nothing in the network which will block this. Are you sure that it looks for dialtone whilst the call is up? I’m not saying it doesn’t do it.
Your voltage levels problem is that you are using a line intended for connecting to a phone, whereas you need a line intended for connecting to another PABX. Ordinary phones cannot detect when the caller has hungup; they rely on the callee doing that and then hanging up themselves. If you, for example, use a modem on such a line, it relies on failing to detect carrier from the far end, rather than detecting a supervision tone, to determine that the call has ended.