Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

How many d-channels necessary for 2 ISDN PRI T1s?

I have an NFAS group configuration of 4 channelized T1s. serial 0 carries the primary d-channel, serial 1 carries the secondary, two and three care 24 B interfaces. If I lose serial, who carries my secondary d-channel, will the other 3 T1s be operational?

Is it possible to have more than one T1 operational if your backup d-channel is down?


Cisco Employee

Re: How many d-channels necessary for 2 ISDN PRI T1s?

ISDN NFAS allows a single D channel to control multiple T1/PRI interfaces. If you loose Primary D channel, secondary D channel will become active and if you loose both the d chans (primary and secondary) then all the calls which are connected will remain connected but no now calls will be received or placed. But loosing primary ans secondary both togather will be very rare from telco side..Unless telco is very funky..All the T1/PRI's can receive and place calls as long as one D channel is active.

But i think primary and secondary chans will be good enough in your case.

CreatePlease login to create content