Telco chopping off leading 0 of incoming calls?

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Sep 19th, 2007
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Hi. I've noticed that our incoming calls have the leading 0 digit chopped off them. IE 02920 111111 is appearing as 2920 111111 . Obviously when we miss a call and try to redial it wont connect because the number is invalid.

I've done an ISDN q931 debug and it appears that the number is coming in from the telco, in this case BT, with the leading 0 digit removed.

Is my call manager stripping it off the leading 0 or is BT not supplying me with a complete number?


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Overall Rating: 5 (2 ratings)
davieshuw Wed, 09/19/2007 - 07:00
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The result of the sh isdn q931:

ISDN BR0/1/0 Q931: RX <- SETUP pd = 8 callref = 0x01

Sending Complete

Bearer Capability i = 0x8090A3

Standard = CCITT

Transfer Capability = Speech

Transfer Mode = Circuit

Transfer Rate = 64 kbit/s

Channel ID i = 0x89

Exclusive, B1

Calling Party Number i = 0x2181, '2920433599'

Plan:ISDN, Type:National

Called Party Number i = 0x81, '447512'

Plan:ISDN, Type:Unknown

Sep 19 14:55:48.520: ISDN BR0/1/0 EVENT: process_rxstate: ces/callid 1/0x1E calL

Sep 19 14:55:48.520: ISDN BR0/1/0 EVENT: host_incoming_call: call_id 0x001E, Gu0

Sep 19 14:55:48.532: ISDN BR0/1/0 Q931: TX -> CALL_PROC pd = 8 callref = 0x81

That calling party number is actually 02920433599.

davieshuw Thu, 09/20/2007 - 08:37
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I've contacted the Telco.. they say its not them....

iwearing Thu, 09/27/2007 - 06:19
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I have the same issue. Apparently it is common for telco's to only forward 10 digits inbound.

Aparrently a leading 0 can be prefixed with a translation pattern.

Did you get a resolution.?.


davieshuw Thu, 09/27/2007 - 07:56
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Well that seems to be it.. do you have a linK to a CME document? unfortunatley that only deals with CCM :(

icabrera Thu, 09/27/2007 - 22:47
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Hi, at the same document you can see how to add the digit with a h323 gateway too, and this is your case if you are working with CME.


auditcommission Wed, 10/31/2007 - 05:23
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We got to the bottom of this issue with BT, after a lot of digging.

Apparently it's down to Q931 and Q931e circuits. Q931 signalling allows all the digits including the leading zero to be sent by the Telco. Q931e is the more modern version, and because the Telco apparently can't tell whether the call originated internationally or nationally, it doesn't include the leading zero.

BT can now only supply Q931e circuits, so you have to do other translations to get the leading zero visible. If you went to a supplier such as Cable and Wireless, they can still supply Q931 circuits and you get the leading zero.

paolo bevilacqua Wed, 10/31/2007 - 05:35
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I would be curious to learn how exactly q931e differs from the standard...

Actually q931 does not mandates with which parameters telco must deliver a call, it just defines the parameters to do so.

As a comparisonI can tell how it works in another EU country:

The default standard is to send calling without the zero, but with type national, so you build you rule on here to add digits needed for recalling.

International calls are correctly identified as so in setup message for you to add the international access code.

Another carrier emulates the above verbatim.

A third one, just sends type unknown with the leading 0 for national calls, it also signal international correctly.

To me seem the above was made to make it easier to program equipment as no digits has to be added to incoming.


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