Polarity Switch Causing False Call Backs


With DAHDI analog lines, I keep getting false call backs after putting the phone down due to the reversal in line polarity triggering the lookup of a caller ID.

I’ve tried using hanguponpolarity switch, but that causes a hangup when answering the phone.

How do I go about getting the polarity switch at the end of a call to cause a hang up, but not at the start of a call?

First of all if your telco signal the beginning of the call with a polarity reversal, you should use the following


then try again with the hanguo polarity.

Try this in your dahdi config:

; Span 1: WCTDM/0 “Wildcard TDM410P” (MASTER)
;;; line="1 WCTDM/0/0 FXSKS"
channel => 1



; Type of caller ID signalling in use
;     bell     = bell202 as used in US (default)
;     v23      = v23 as used in the UK
;     v23_jp   = v23 as used in Japan
;     dtmf     = DTMF as used in Denmark, Sweden and Netherlands
;     smdi     = Use SMDI for caller ID.  Requires SMDI to be enabled (usesmdi).
; What signals the start of caller ID
;     ring        = a ring signals the start (default)
;     polarity    = polarity reversal signals the start
;     polarity_IN = polarity reversal signals the start, for India, 
;                   for dtmf dialtone detection; using DTMF.
;                   (see doc/India-CID.txt)
;     dtmf        = causes monitor loop to look for dtmf energy on the
;                   incoming channel to initate cid acquisition

You will have to check with  your provider as to what to expect from them, but I don't think that




are  appropriate options for you.

I suggest:-


for UK BT lines.

I’ve lived with the issue up to now by sending anything with no CID to an IVR which times out after a few seconds and hangs up the line. This seems to working normally as far as the users are concerned, but I’d really like to get it sorted properly to put an end to these phantom incoming calls.

I’m wondering if it’s voltage related. On outgoing calls, when connected the line is at 9v. If the other end hangs up first, the polarity reverses but stays at this low voltage. Everything is normal.

However, the problem occurs when I hang up first my end. The polarity reverses, but as the line is now idle it also changes from 9v to 50v. It’s only when we get a polarity change AND an increase in voltage together than this “starting post polarity CID detection” is incorrectly triggered.