Fractional PRI MGCP 2801

[miket]

I have a fractional PRI running MGCP mode on a 2801 using a Vwic 1 mft t1, what is the best way to turn off the unused DS0's??? Make Channel B status in CallManager or use a group in the gateway like 1-12,24 ???

[thisisshanky]

Under service parameters (callmanager), click Advanced button and search for B channel maintenance.

There should be up to 5 B channel maintenance that you may specify. Copy the name of the MGCP endpoint from the gateway confiuration page and paste it in the b channel maintenance field.

= 0000 1111 1111 1111 1111 1111

0 - active channel

1 - busied out

You should have only the top 4 channels up and running now.

Also make sure the MGCP gateway config page has "Enable status poll" checked.

HTH

Sankar.

PS please remember to rate posts

[anup.anand]

You would need to do both steps. You have to create the group in the gateway for the active channels, say 1-12, so that Layer 2 using Q921 will be setup properly between the gateway and the telco ISDN switch. You also need to use the Channel B status to tell Callmanager to use only those channels (1-12) for calls.

Regards,

Anup

[s.casper_2]

Ok but what if you want to use fractional PRI/T-1s for more than 5 gateways?

[thisisshanky]

I have never tried that. You have only 5 MGCP maintenance channel options available right now. I guess you could rely on H323 on the remaining.

HTH

Sankar

PS: please remember to rate all posts!

[s.casper_2]

Wouldn't the Call Manager "know" the channels that are not in use? I think that if the carrier is providing you B-channels 17-23 with 24 as the D-channel that the remaining channels would appear out of service and the Call Mananger would not try to use them. Al least I hope that is how it works - H.323 does not scale well for dial peers in a large multi branch network.

[gajolly]

i dont think that callmanager will come to know whether the call should go through the unused channels or not, it should be configure on the callmanager as SANKAR already explained under advance options.

[s.casper_2]

Too limited for an enterprise deployment, if that is the only option. If the carrier is sending that a B channel is out of service or not provisioned and the PRI is backhauled via MGCP I do not see why it would be selected for an outbound call by Call Manager. Have to test.

[michael_davis]

Unfortunately CCM does not know. According to Cisco, MGCP controlled fractional ISDN circuits are not supported. The service parameter is for temporary maintenance only.

The reason this doesn't work is that CCM is controlling the D-channel for that PRI, not the gateway. CCM assumes control of all the B-channels and D-channel(backhaul). The gateway no longer controls the D-channel.

In fact, if you use ccm-manger config / ccm-manager config server commands, ccm-manager will download a config that places all 24 timeslots in service, regardless of the fractional timeslots you configure in the cli.

So why would you configure a fractional PRI on an MGCP gateway's CLI? Because during fall-back to H.323 mode for SRST, the ccm-manager will restore the fractional pri-group portion of the config for the duration of SRST activity.

If you want H.323 to scale, you should consider centralizing your dialplan with gatekeepers.

Let me know if this helps explain by rating the post.

Michael

[shane]

According to a TAC engineer that I spoke with one day a fractional PRI is really not supported with MGCP backhauled PRI configurations. However it does work. I have many PRI's running fractional and I have configured both example - 1-12,24 if it is not backhauled and if it is backhauled Call Manager does not know it is a fractional but the only thing you need to consider is the Top/Bottom vs Bottom/Top channel selection on the gateway so it does not try to grab a channel that is offline first.

[miket]

I talked to TAC the other day and they said to use make b channel in order fo the fractional T1 to be supported..

I have always done it with the service groups. There is a whole other topic on whether to use the ccm config server command.. SOme people say use it some say don't..

But thanks for all the replies

[michael_davis]

Sorry, I'm not sure I was clear in my earlier post...

When I said it doesn't work, I was referring to the earlier question "Wouldn't the Call Manager "know" the channels that are not in use?."

The config server reference was simply to illustrate that point.

In terms of support, see:

http://www.cisco.com/en/US/partner/tech/tk1077/technologies_configuration_example09186a00801ad22f.shtml#req

http://www.ciscotaccc.com/voice/showcase?case=K14305072

CSCed41207 and CSCdw29259.

HTH clarify a bit.

Michael