[Asterisk-Users] UK, Disconnect supervision

[Peter Hoppe]

Hello!

This is actually less a question than some information, if anyone else 
struggles with the same issue.

I am located in the UK and use a Sipura-3000 adapter to connect to a BT 
line (via fxo port). One problem I had was that disconnect supervision 
didn't work:

Some caller phones me (my adapter)
adapter goes off-hook (answers call)
caller hangs up
adapter doesn't realize and stays off hook.

I researched into it and found that the BT exchange delivers a CPC (0.1 
sec) upon the caller's hangup and a disconnect tone about 3 seconds 
later. The tone lasts 6 seconds and remains constant during that time. I 
recorded the disconnect tone with Cool Edit and did a frequency analysis 
on it and got the following components:

     400Hz/-56dB +
     1200Hz/-69dB +
     2000Hz/-65dB +
     2800Hz/-59dB +
     3600Hz/-59dB

If normalized with -56 dB reference level, I get

     400Hz/0dB +
     1200Hz/-13dB +
     2000Hz/-9dB +
     2800Hz/-3dB +
     3600Hz/-3dB

I suspect that the harmonics (1200, 2000, 2800, 3600)Hz may not have 
come from the Exchange, but were distortions.

After the 6 seconds the tone stopped and there was succession of two 
'clicks' on the line (another CPC? haven't looked into that); both were 
0.3 secs apart.

I tried to use both, the CPC and the disconnect tone in the Sipura-3000 
settings. Unfortunately I couldn't get disconnect supervision via the 
disconnect tone to work. In a post on the voxilla forum

http://voxilla.com/PNphpBB2-viewtopic-t-2904.html

I found some further info on disconnect tone in the UK - unfortunately I 
couldn't get those settings to work. I also looked into BT's SIN notes 
(on http://www.sinet.bt.com , notes 350, 351) but failed to see further 
information on what tone they exactly deliver for a disconnect event.

However, the CPC did work. I set the adapter to a CPC minimum time of 
0.05 seconds, and from then on it recognized remote disconnection in 
every test phone call. If I set the time too short I got problems - for 
incoming calls the adapter started to mistake the incoming ringing for 
disconnect events and simply wouldn't go off hook anymore.

Now, these are the settings I configured my adapter with:

Settings: 
spa-3000-setup-web-page/PSTN-line-tab/PSTN-disconnect-detection-section:

'Detect CPC' => 'yes'
'Min CPC Duration' => '0.05'

I also have
'Detect Disconnect Tone' => 'no' [as it didn't work]
'Disconnect Tone' => '400 at -30,400 at -30;5(5/5/1+2)'
'Detect Polarity Reversal' => 'Yes'
'Detect PSTN Long Silence' => 'yes'
'PSTN Long Silence Duration' => '150'
'Detect VoIP Long Silence' => 'no'
'VoIP Long Silence Duration' => '30'

but the relevant values are 'Detect CPC' => 'yes' and 'Min CPC Duration' 
=> '0.05'


I hope this helps, if anyone struggles with unrecognized disconnects.

God bless, Peter


CPC: Calling Party Control: A short break in the line current in the 
called party's phone line when the calling party hangs up.
(def. from http://www.vikingelectronics.com/glossary/telecom-term.php)
-- 
dyslexics of the world - untie !