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2 x T1 PRI with only 1 D channel configuration

Normally our configuration for a single T1 PRI on a H323 gateway is:

card type t1 0 0

network-clock-participate wic 0
network-clock-select 1 T1 0/0/0

isdn switch-type primary-ni

controller t1 0/0/0
cablelength long 0db
pri-group timeslots 1-24

interface Serial0/0/0:23
no ip address
encapsulation hdlc
isdn switch-type primary-ni
isdn incoming-voice voice
no cdp enable

voice-port 0/0/0:23
echo-cancel coverage 64

We will be activating another T1 PRI on 0/0/1 and 0/0/0 will no longer have a D channel.

I've been reviewing these articles though I am still not sure what the configuration should be.

Does anyone have experience configuring 2 T1 PRI circuits with only 1 D channel?


Hall of Fame Super Red

2 x T1 PRI with only 1 D channel configuration

Hi Mike,

We only use PRI's with a 1 to 1 D-Channel relationship, but I thought

this doc may be helpful for NFAS;



Hall of Fame Super Gold

Re: 2 x T1 PRI with only 1 D channel configuration

With only 2 PRIs only, having only 1 D-channel, does not gives advantage and is not a good idea.

Ask yourselff, what happens if the circuit carrying D goes down ?

So, to avoid disaster, one wants D-channel backup, that is feasible with NFAS.

But, you end having again. 2x Ds for 2s PRIs.

That's why NFAS is not advantageous with 2 PRIs and no D-backup, ad it gives you 47 beares instead of 46, but much bigger chances of total failure.

And of course, if you get D-channel back, you have not gained any additional channel, but got the additional complexity of NFAS.