Multiple PRI Groups on single T1 interface

Unanswered Question
Jun 12th, 2009

Hi All,

I have come across a situation where another equipment is being replaced with a Cisco 2821 router with VWIC2-1MFT-T1 card.

The previous equipment is configured to receive voice calls on first 10 channels but sends back any voice calls only on the remaining channels.

Is there a way to configure the same on the router like some sort of pri group where the pots dial-peer could be made to point to some sort of group or even if it is possible to force a dial-peer to use one or a particular group of challels?

I am interested in any solution and it is urgent.

Due to the urgency I will be folling any replies and test them throughout the weekend so any help will really be greatefully appretiated.

Many thanks in advance for any help.


I have this problem too.
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Overall Rating: 4.7 (3 ratings)
Kenneth Mohammed Fri, 06/12/2009 - 07:25


Basically the command to do this is:

controller t1 x/x

ds0-group 0 timeslots 1-10 type e&m-wink-start

ds0-group 1 timeslots 11-24 type e&m-wink-start

Then on your outgoing dialpeers configure:

dial-peer voice 1 pots

destination-pattern 9[2-9]......

port x/x:1 (remaining channels for outbound)

forward-digits 7

dial-peer voice 2 pots

destination-pattern 91[2-9].........

port x/x:1 (remaining channels for outbound)

forward-digits 11

Hope that helped, if so please rate.

ShailendraK Fri, 06/12/2009 - 07:43

Hi Ken,

Thanks for the reply. I will be reaching work in about 3 hours time. I will post back the result immediately after testing.

And I will make sure I rate your responce.

Thanks for the help matey.



Paolo Bevilacqua Fri, 06/12/2009 - 08:16


In your answer, you assumed the OP has CAS, while I've assumed it has PRI.

In reality we don't know what he has, so that should be clarified.

Paolo Bevilacqua Fri, 06/12/2009 - 08:10

You do not need multiple trunk groups to achieve the above.

First of all, the router has no control on which channel it receive calls.

To limit the number of outgoing calls, just configure max-conn 20 unde the outgoign DP.

Kenneth Mohammed Fri, 06/12/2009 - 08:43

Hey Paolo,

Thanks for the clarification. I did assume CAS T1 since he was saying that he had some channels dedicated for incoming while others were dedicated for outgoing. Also, I wasnt sure whether or not this would be possible with ISDN PRI.

Paolo Bevilacqua Fri, 06/12/2009 - 08:56

You can have multiple pri-group off a same controller, or be OK with the simple config I've suggested above.

ShailendraK Fri, 06/12/2009 - 09:05

Hi guys,

Thanks for your replies. I am following them but still haven't reached work.

Paolo you are right buddy. It is PRI. And I can see your solution will work in my situation. I will get back soon.

I am also interested to know if it is actually possible to configure groups like Ken suggested for CAS.

Thanks again.


Nicholas Matthews Fri, 06/12/2009 - 09:10

Hi Shad,

For partial PRIs you probably want to configure the pri-group as such. That way the router does not try to send calls out channels that aren't accepted on the other side.

controller t1 0/0/0

pri-group 1-8,10-16,23

If you're using MGCP you want to use the full 1-24 and then busy out the channels in CUCM so that ccm config doesn't overwrite it. Otherwise this is fine.


Paolo Bevilacqua Fri, 06/12/2009 - 09:20

pri-group 1-8,10-16,23

That is really a strange configuration. Perhaps router will not use the excluded channels, but what if a call comes in there ?

The proper configuration is either max-calls, or multiple pri-groups encompassing all the channels.

Nicholas Matthews Fri, 06/12/2009 - 10:05

We see this every now and then when people have two partial PRIs. Technically the other side should be configured the same so you don't have the incoming problem. This prevents having to manually busy out channels and may be a bit more graceful. Just another way to skin the cat.


Paolo Bevilacqua Fri, 06/12/2009 - 12:18

I sure believe you, but there isn't anything less graceful than changing B channels on PRI, since you have to stop all calls, shutdown voice-port, remove group and then re-add port where it was referenced.

Also I think that if you ask a telco or PBX technician to setup so certain channels are skipped on a PRI, you better have tolerance to profanities.

ShailendraK Fri, 06/12/2009 - 13:08

Hi All,

Thank you for the help. So as a simple solution the suggestion by Paolo is working. I have configured as follows.

The other side is sending the calls only on the first 10 channels.

On my router I have configured the follows.

interface serial 1/0:23

isdn bchan-number-order descending

This makes the 2811 send the calls from the bottom channels in descending order. Configuring the max-conn on the outgoing dial-peer is sending the calls only on the required the channels back to the network.

Thank you very much Ken, Paolo and Nick. Out of interested is there a way to configure groups of PRI and send calls through them? For example if there is a tenant situation where as a managed service provider there can be a full T1 from one provider. Is it possible to split it into different groups and send calls through them respectively?

Thank you very much



Paolo Bevilacqua Fri, 06/12/2009 - 21:43

Yes, as mentioned above, multiple PRI groups groups should be supported. However, it is not of much use because in your example, telco will not know anything about multiple groups, and will place all calls on the lowest free channel anyway.

Please remember to rate useful posts with the scrollbox below.

ShailendraK Sat, 06/13/2009 - 00:34

Hey Paolo,

Are you referring to Ken's example? I am interested to know how the same can be done if PRI is being used? Will you be kind enough to provide a few lines of configuration or even refer to the commands or a doc?

Thanks for all the help in the meantime.



Paolo Bevilacqua Sat, 06/13/2009 - 00:48

Under controller, configure multiple pri-groups using non-overlapping channels. That's all. Ken's example is about CAS that luckily you don't have.

Again, in most cases it doesn't anything good for the reasons explained above.

ShailendraK Sat, 06/13/2009 - 01:04

Hey Paolo,

I have scratched my head enough and tried the commands I could find. What Nick suggested is the closest I could get but this does not give me any flexibility in sending out the calls through only a set of channels as only one voice-port shows up in the configuration.

Any commands you could help me out with mate? I will be grateful.



Paolo Bevilacqua Sat, 06/13/2009 - 01:07

Sorry, I can't understand what your problem really is.

Can you configure multiple pri-groups ? If not, may be the IOS you use doesn't have the feature.

And, again for the 5th time, it is not necessary to have multiple pri groups to limit number of outgoing calls. Do you understand that ?

ShailendraK Sat, 06/13/2009 - 08:34

Hey Paolo,

Let me first clear your doubt that I am not trying to use PRI groups to limit the outgoing calls anymore. I don't know what in my recent posts gave you this idea. As I mentioned in my previous post that using max-conn obviously did the job.

Anyway, the commands I was looking for are as follows. Unfortunately they never showed up anywhere in the searches when looking for multiple PRI groups. Hope these help someone else too.

controller T1 0/0/0

framing esf

linecode b8zs

pri-group timeslots 1-24

trunk-group GROUP1 timeslots 1-10

trunk-group GROUP2 timeslots 10-18

trunk-group GROUP3 timeslots 19-23

Thanks again guys. Enjoy your weekend Paolo.



Paolo Bevilacqua Sat, 06/13/2009 - 08:39

You are right, it's not multiple pri-groups, but trunk-groups under controller. I couldn't remember because I never use it.

Now please let me understand what advantage that gives you :)

ShailendraK Sat, 06/13/2009 - 08:44

As mentioned in my previous posts I was just interested to find out how to to this.

It does not give me any advantage in this particular scenario. Just good to know how the multiple PRI groups could be configured since they were mentioned in this post. My main issue was resolved by your suggestion earlier.


Paolo Bevilacqua Sat, 06/13/2009 - 08:49

Curiosity is (almost) always a good thing. I've rated your post above.

Thank you for the appreciation and good luck.

skint Thu, 06/16/2011 - 08:14


I just found a use for it, thanks for saving me some time.  A customer had authorization codes at the telco level and needed some FAX machines to not use the codes.  The trunk-groups will allow me to set aside some channels that will not need FAC.  I proposed FAC based on ANI, but that was not an option for the carrier.



John Butterfield Thu, 04/18/2013 - 13:00

      I am trying to use the trunk group command as follows:

controller T1 0/0/0

cablelength long 0db

pri-group timeslots 1-7,24 service mgcp

trunk-group GROUP1 timeslots 1-6

trunk-group GROUP2 timeslots 7

     I need to be able to direct outbound calls to Group1 or Group2, however in Call Manager (9.x) if I try to create a route group pointing to the T1, I am only allowed to choose "All" ports and I don't see a way to route to one group or the other.  Is this possible to direct calls to one group or the other?


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