Fractional t1 pri MGCP and H323 with Call Manager

[moises7777]

We have  a site that has call manager and a 2821 as a voice gateway. The gateway is configured as mgcp. We have four fxo ports and a t1 pri coming into the network. We switched phone providers and attempted to make the change last night, unfortunately we ran into some problems and I hope someone here can help.

We configured the new pri from the CLI. The new pri is a fractional pri so we only set up 15 channels and 1 b channel.  When, we did this, when we attempted to call out, the call would reach the voice gateway but it would drop. At that point, we configured the PRI port as mgcp from the Call manager. Once we did that, our configuration changed from the 1-15 timeslots to 1-24. We soon found out that mgcp does not support fractional T1’s.

We then removed mgcp from that port and set up the voice gateway as h323 so we can  configure the PRI that way. But now when we try to make a call out, the call never reaches the voice gateway, we get a message stating our call did not go through. The call manager seems to not be routing the call to the VG.

I created a route group and added a route list that contained the ip address of the h323 port on the voice gateway, but nothing. It seems as if Call Manager is still managing that port.

I need to be able to set up that PRI via h323 and to configure the dial peers. The dial peers will be easy, but right now I need some advice on how to get the call manager to route the call to voice gateway. Any help would be appreciated thanks in advanced.

[Manoj Srinivas · Accepted solution]

Hi Moises,

As you pointed out, the MGCP gateway does not support fractional PRI. But there is work around for that. Though i wuld say Cisco would not encourage you to use this work around. But this would work fine.

Here is the document which explains you on how to configure fractional PRI on MGCP gateway.

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_configuration_example09186a008076f8d2.shtml

Since this is an MGCP gateway, the CUCM is in control of the gateway and all the configuration has to be done on the CUCM. If you just configure 1-15 channels in gateway, the CUCM will not know about this information and there has to be a way to tell the CUCM that we are using only 15 channels in this PRI.

So the above document will help you on cofiguring that.

If you are looking for H323 configuration, Please delete this PRI configured as MGCP in the call manager and go ahead and configure a H323 gateway in the CUCM.

The below link will guide you on H323 gateway config on CUCM.

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_tech_note09186a0080094636.shtml

Once you have confiured the H323 gateway on CUCM, please choose this gateway under the route-group or route-pattern based on your design.

Please note that after configuring the H323 gateway on the CUCM, it would show as "unknown"

and not as "registered". Also note, you will have to configure the dial-peers on the gateway for the calls to work.

[moises7777]

We really didn't want to do the work around because mgcp still managers some ports and we were concerned that doing the fix would create more problems in the future.

Turns out that since this was a new circuit and it was not all the way up, we needed to provide the calling number in the cucm route pattern. Once we did that it worked.

All you info was spot on though, thanks.