Telco doesn't recognize that PSTN line has been picked up

I’ve got a weird problem and I’m not sure if it’s hardware or software related, I could use some help.

The system consists of a Digium card with one FXO and one FXS for a small business. It’s a genuine Digium card not a Chinese knockoff.

Fresh install of AsteriskNow, configured one trunk, one inbound route, one extension, one outbound route.

Outgoing calls work fine.

Incoming calls are picked up after the first ring by asterisk BUT the telco doesn’t seem to recognize that the call has been answered.

So the telco continues to ring the line and because of the delay asterisk has in picking up the line, the telco reaches three rings before asterisk and sends the call to the telco voicemail. Asterisk still has the line open so after it’s third ring it goes to voicemail and begins recording, what it records is the message being left in the telco voicemail inbox. When it’s all done I have the same message in both inboxes.

My question is this: what tells the telco that asterisk has taken the line off-hook? Is this a hardware thing or does the software send a signal to the telco that the call has been answered?

I need to narrow this down a little, I don’t want to spend all day sifting through software if it’s a card problem but I don’t want to spend $$ if it’s not hardware related. (no spare hardware on hand)

Any help or assistance you can provide will be appreciated.

Thank You in Advance

What country? What telco

North America

Specifically Telus in British Columbia Canada

Does it really matter? Is the method of telling a telco the line is off-hook different in other areas of the world?

The hardware from Digium works all over the world so if you want to know where I am that would mean that you think it’s software right? If it was a hardware signal it wouldn’t matter where I was.

Yes. Some require battery reversal etc.
If you put a meter on the line you should see 48vdc. ~100vac on ring and ~9vdc off hook.
Check the 48 and 9. If you dont get to that 9ish that means you aren’t putting a large enough load on the line (500ish ohms)

The voltage didn’t move at all when asterisk grabbed the line, it stayed at 48.

As a second test I monitored the line while dialing out and the line did drop to 8.4V

I would think that shows that the FXO card hardware is able to load the line and therefore not a hardware problem.

I monitored the voltage as I called from another line and this time I answered it, as soon as I picked up the set the voltage dropped to 8.4V.

I’m a bit confused by this, I thought asterisk was supposed to take the line off hook as soon as it received it and before it started ringing the extension.

Do you have a virtual DID assigned to the FXO ports and an inbound route to send them to?

The line is not answered as the callerid is being spilled or waiting to be spilled so make sure you have your callerid detection set up right also

Do you have a virtual DID assigned to the FXO ports and an inbound route to send them to?

No I don’t.

Thanks Dicko and TheJames

All I had to do to solve this was dial *94 to my telco and enter 6 to delay the telco voicemail to 6 rings. Now Asterisk has enough time to ring the extension three times and then go to voicemail without interference by the telco.

Interestingly asterisk doesn’t load the line while the extension is ringing, it waits until the call has been transferred to voicemail and then the voltage drops to 8.4V


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