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Unread 09-30-2006, 05:01 PM   #1
Join Date: Sep 2006
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Default Argh! Outgoing PSTN nightmare with 488

Hi all

I have a (new) Handytone 488.

I have registered with various SIP provider and can make/receive calls. I can receive PSTN calls.

I CANNOT make PSTN calls!

I cannot, however, make PSTN outgoing calls. It drops a connected call after about .5 a second.

Bizarrely, if I connect the outside line, and ring "***", I hear the Telewest "attendant" saying "The number you called" etc, perfectly fine.
If I connect outside and ring 123, and it picks up, one end drops the call.

SYSLOG from the first example (in reverse order) :

1367DAA Hangup 2
FXO killcall 0 1 33251 0
1367DAA Hangup 4
1350DAA Pickup 2

SYSLOG from the second example (in reverse order) :

1367DAA Hangup 2
(I hangup handset here)
1367DAA Hangup 2
FXO killcall 0 1 0 0
1350DAA Pickup 2

Something (killcall) kills the call, and I see a Hangup "2" rather than a "4". I also see another "2" when I actually disconnect the handset.

I suspect this is something to do with voltage and impedance.

Port FXS (the handset) has the following options :

Onhook threshold : 800ms
FXS Impedance : UK/New Zealand #2 (370 Ohm + 620 Ohm||310nF)
Onhook Voltage : 36V
Polarity Reveral : NO

Port FX0 (the line, connected to Telewest) has the following options :

PSTN AC Termination : 370 Ohm + (620 Ohm || 301nF)

Now, the Telewest FAQ says (on Network Termination Impedance) :

The impedance necessary to satisfactorily terminate the Telewest network interface at the NTP so as to prevent instability is represented by a three-element network consisting of a 620 ohm resistor in parallel with a 310 nanofarad capacitor, both in series with a 370 ohm resistor.

My FXS Impedance matches this.

My handsets are cordless DECT, but I have tried with a wired handset. No difference.
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