in Telephony

supervised disconnect on PSTN lines

It’s funny how sometimes you have a technical problem that you think is only attributable to your own (possibly crappy telephony) setup, but later on you discover that the problem is quite common. For example, today on the TAUG mailing list, someone complained about their Zap (analog) channel never being hung up by Asterisk particularly when the user at the other end hangs up right away. I have also had this problem on my home Asterisk setup, where Asterisk will busy-out the Zap channel for hours, preventing people from making incoming calls.

At first I attributed it to my crappy clone FXO card, but now I’m wondering if it’s a problem with Asterisk. Others seem to think so and feel that Asterisk doesn’t properly handle the supervised disconnect in situations when the channel hasn’t been Answer()ed. I haven’t done enough tests to nail down when in the dialplan it happens exactly.

Later in the day, someone claimed that one way to fix the root cause is to teach Asterisk how to handle the standard off-hook warning tone, but I don’t think it’ll be very simple to implement, since the warning tones are probably different for each country.

For now, I’m happy to ssh into the server and soft hangup Zap/1 (as someone suggested) but I wish there was a solution that didn’t require such manual intervention, so if any telephony enthusiasts are reading this and have any better ideas, feel free to comment.

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