ISDN Dialing - Erratic Behaviour

Unanswered Question
Feb 18th, 2008


Network Design as follows -

• Individual branches dial and establish a connection to the Central Location; in case of its primary leased line failure between the Branch and Central Location.

• Central Location dials and establishes a connection to the Data Center. in case of its primary leased line failure between the Central Location and Data Center.

• All branches are spread across the Country and have been activated with STD calling (Interstate dialing / calling).

Problem facing -

• One of the Branch with 2801 Router+2BRI S/T card + 12.4(3B) IOS dials and establishes connection to the Data Center which is located in a different state successfully.

• But this above branch does not dials a test call to its Central Location; which is again located in a different state. (Point to be noted: "STD Dialing is activated on this Branch, that's why it is able to make a call to the Data Center successfully, but fails making a call to the Central Location *01202775453*").

Can any one please HELP me to rectify this issue.

Please find the attached Debug q931 & q921 output of the Branch router when dailed *01202775453* and fails.



I have this problem too.
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spremkumar Mon, 02/18/2008 - 19:44


Have you checked the configurations of both the central location which requries to accept the call and the other location which is already accepting the call from the branch ?

But as per the error message this is something to do with your central location's telco settings which you need to contact either BSNL/MTNL to get it resilved.

C1 - Bearer capability not implemented

The network cannot provide the bearer capability that the user requests.

Contact the telco to troubleshoot further.


keshavahp Mon, 02/18/2008 - 22:51

Hello Mr. Prem,

Thanks for responding!

I have checked with BSNL at Central Location - they claim that all calls are allowed on the PRI link of Central Location and no such restrictions have been configured.



dongdongliu Mon, 02/18/2008 - 20:42


are you sure that the switch-type and spid number are both set right?

keshavahp Mon, 02/18/2008 - 22:41

Hello Mr. Liu,

Here in India Telco's will not use the SPID no#, hence SPID's are not configured.

ISDN Switch type is configured with the right one *basic-net3*.

Can this be a IOS Bug?

dongdongliu Tue, 02/19/2008 - 04:42

hi Keshava

It seems the L2 is well(from router to isdn switch), but, what`s about L3 info?

could you show us "show dialer/isdn status & debug dialer" info?

thank you



yxsjwsb Wed, 02/20/2008 - 09:24

Hey, I'd use the pri debugger tool (free - ) to keep up with that failures. It may reveal that only certain B chans are affected.


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