Reducing Channels from a full PRI to a fractional PRI

Unanswered Question

Hello All,

I have a 3725 router configured as H.323 with a full PRI connecting to PSTN. The PRI is being under utilized so I have decided to reduce the channels to 11 B channels and a D channel. I've talked to my provider about applying the change and they said that the change is seamless and will not affect service at all but I am a little iffy about this.

Can someone please confirm the following for me ?

1. Does the change on my router and the provider's equipment need to be applied at the same time ?

2. Will there be any service down time ? I thought the pri-group timeslot has to match on both ends for the D channel to come up.

3. I'll be reducing the pri to 11 B channels and the provider has told me that the D channel will remain on the 24th channel. Do I just simply change the pri-group timeslot from 1-24 to 1-11 ?

The PRI is conneced to an NM-HDV with a VWIC-1MFT-T1.

thank you very much in advance !!


I have this problem too.
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Kenneth Mohammed Mon, 03/31/2008 - 13:45

To minimize downtime, it would be best to schedule a time to do the cutover. Basically, all that needs to change in the router is the pri-group statement. You may also want to shut/no shut the controller t1 as well. Your PRI group statement will need to say:

"pri-group timeslots 1-11"

In the running config, it will automatically apply the D channel to the statement, so it looks like:

"pri-group timeslots 1-11,24"

Hope this helps.

Hello Kenneth,

My provider they pretty convince that the change is seamless and that there will be no service affecting, they even said that they could even make the change ahead of time on their end and I can apply the change on my end at my own convenience. Can you tell me if this is true ?

thanks Kenneth !!! I appreciate your response !!


Kenneth Mohammed Mon, 03/31/2008 - 14:19

To be honest with you, I'm not really sure. Maybe one of the gurus can jump in and answer that for you. I guess maybe you can try it during non-production hours to find out for yourself. If your PRI is configured for 23 channels now, change the timeslot statement in the gateway to 1-11 and see if you can still make/receive calls. Everytime I've done a cutover, I coordinated a time with the telco so that in case something goes wrong, I have them there on the phone with me, as opposed to having to open a trouble ticket to get the issue resolved and increase your downtime.

Paolo Bevilacqua Mon, 03/31/2008 - 14:48

Ok, please don't call me guru, here's the scoop on the matter. Changing timeslots is not really "on the fly", but almost.

Here's the sequence, even if you didn't knew that router would guide you anyway.

# 1. note any DP that is using port x/y/x:23 in destination-pattern: show dial-peer voice summary | inc x/y/z:23

voice-port x/y/z:23


# 2. note any config possibly had under voice-port

controller t1 x/y/z:23


no pri-group

pri-group timeslots 1-11

no shutdown

# 3. reapply config under voice-port in .2.

# 4. reapply port under any DP noted in .1.

One thing to note is that if you know that telco always place calls to router on the lowest available channels (that is very standard practice), you can reduce timeslots before telco does, and nothing bad will happen. Else if telco is using cyclic hunting, the switch must be coordinated.

Hope this helps, please rate post if it does!


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