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questio About ISDN BRI Layer1 status and monitoring


CIsco 2811

I have a problem on isdn bri connection customer can't use the line sometimes. The only thing that I was able to detect is that the ISDN layer 2 goes down, deb isdn q921 show that). Is it possible understand if aslo Layer goes down ? It seem that layer1 still up (Show isdn status). From my experience I saw that puting out the cabling of a Bri that was working the layer2 goes down, but the layer 1 still up into the router. At the is it possible monitoring the layer1 in real time.

6 Replies 6

paolo bevilacqua
Hall of Fame
Hall of Fame


are you connecting to TI ?

It is normal that layer 1 & 2 get deactivated after a short timeout of non use.

The only things you should care is :

1. use an updatad IOS to avoid bugs - what do you have now ?

2. use isnd tei-negotiation preserve.

Then if still trouble, use debug bri together with debug isdn q921.

Hope this helps, please rate post if it does!

Cisco Employee
Cisco Employee

This sounds a lot like Cisco bug CSCsg11155 - Hung Calls on BRI port.

This should be fixed in IOS 12.4.15T1 or 12.4.16a

Something else to watch for with BRI services - many Telco drop layer after a period of inactivity as a power save feature. You can often contact the telco and request they make the BRI a 'persistent layer 1 ' connection so layer 2 traffic is continually passed between the exchange and the terminal device.

In our case there isn't Telco part.The 2811 router is used as h323 GW and the BRIs' router are connected to the Customer PABX. We see that layer2 goes down also during conversation, but we aren't able to detect if is due to some layer1 problem (microinterruption for example). As told we saw layer1 always up evenif we put out the cabling between ROUTER and PABX. We are able to see layer1 deactivated just during 1st installation or if after put out the cabling we perform shut and no shut of the BRI interface. So if I understood well with c2800nm-ipvoice-mz.124-6.T6.bin doesn't exit way to monitoring layer 1 problem or is it possible use some counter as for controller E1?

Thanks in advance.


since the router is network side, you will see always layer1 up.

Please recheck cabling and use the properly wired bri cross connect with two pairs only.

Then check show interface for errors.

Then finally I would suggest you to use 12.4(11)XJ4 that is stable for ISDN including network-side applications.

about Layer 1. If you configure the interface as Point to Multipoint ( No isnd static tei 0) and you connect the BRI to a Telecom Italia interface the Telcom Italia after a time with no traffic they tear down Layer 2 an 1 bay default and after that the cisco BRI interface still block. I solved the problem with this additionial option isdn tei-negotiation first-call.added to general configuration

Jorge Armijo

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Jorge Armijo

Please remember to rate helpful responses and identify helpful or correct answers.

-- Jorge Armijo Please remember to rate helpful responses and identify helpful or correct answers.
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