Partial PRI and H323 GW

Answered Question
Jan 12th, 2010

All,

Are current setup is that the main site is an H323 gateway and all the remote sites are MGCP gateways.  Our main site currently has 5 PRI's.  The telco is wanting to take one of our PRI's and divide it up into 3 different groups of 8 channels each due to some local dialing issues (local calls actually have to be dialed as LD for some sites and not for others depending on what area of the county you are in).  Is this possible?  Has anyone done this before and if so how difficult is this to implement.  We are currently running CUCM 6.1.1.

Thanks,

Debbie

Correct Answer by asandborgh about 7 years 1 month ago

Debbie,

To my knowledge this can't be done with a PRI since you can only assign one pri-group to a controller.  However, if this is actually a T1 CAS circuit (indicated by the fact you mention 3 groups of 8 channels=24) I think you could use 3 ds0-groups, although I have never done what you describe.  Are you sure thay are talking about a PRI?  You aren't running NFAS on this are you?

HTH,

Art

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Correct Answer
asandborgh Tue, 01/12/2010 - 11:39

Debbie,

To my knowledge this can't be done with a PRI since you can only assign one pri-group to a controller.  However, if this is actually a T1 CAS circuit (indicated by the fact you mention 3 groups of 8 channels=24) I think you could use 3 ds0-groups, although I have never done what you describe.  Are you sure thay are talking about a PRI?  You aren't running NFAS on this are you?

HTH,

Art

Paolo Bevilacqua Tue, 01/12/2010 - 12:04

Can you give more details ? How telco would know from where you are calling, is calling since it is a single PRI ? Does it depends from the calling number, and how exactly ?

Also, can you get proof that this requirement is legal on their side ?


For the router is possible in extreme cases to split a PRI, but unless it is proven that is a 100% necessary, I do recommend against.

dbritoosis Tue, 01/12/2010 - 12:16

How this came about was the telco screwed up.  They told our company we would save money by putting the PRI in at our site.  When they put the PRI in they ran it off one of their switch's that was not local to us which was fine but their switch was also not local to two of the three sites that were to use this PRI (even though they are all located in the same area code some sites still have to dial long distance to reach each other).  So to fix their screw up they decided to come up with the bright idea of splitting the PRI channels into 3 different groups thus assigning each group of channels to a switch that was local to each location.  I did not think that it could be done, or let me say I had never seen it done, but the Telco insisted it could.  I just verified with TAC that the only way we could accomplish this is with a T1 CAS circuit.

Thanks again for the help!

Debbie

Paolo Bevilacqua Tue, 01/12/2010 - 15:10

It can be done with PRI also, but is rarely done.

Please share some detailed information from telco of what they would expect exactly, and how the can split a PRI to three COs on their side.

I think the person you are talking with does not understand the difference between PRI and CAS, but they also could be able to pull some magic just like the router does.

dbritoosis Tue, 01/12/2010 - 18:21

I am waiting to hear back from the Telco.  I am now curious too since they told me earlier this evening that they could only deliver full PRI's and not a partial one.  Also I did hear back from TAC again stating this is possible to do with an H323 gateway.  Here is what they have come up with:

                                                                                |----MGCP-----Site A GW

                                                                                |

PSTN - - - -PRI 0/3/0- - - GW - - - -IP - - -                |----MGCP - - -Site B GW

                                                                                |

                                                                                |

                                                                                |-----MGCP----Site C GW

We want to allocate channels 1-8 to Site A, 9-16 to Site B and 17-23 to Site C . To do this, we will need to do the following:

1.       Convert all the Gateways to H.323.

2.       Create trunk groups:

Config t

Trunk group SiteA

Trunk group SiteB

Trunk group SiteC

3.       Under the controller t1 0/3/0 add:

Pri-group timeslots 1-24

Trunk-group SiteA timeslots 1-8

Trunk-group SiteB timeslots 9-16

Trunk-group SiteC timeslots 17-23

4.       Create cor lists to ensure that the correct channels are selected by the Site which is placing the call:

Dial-peer cor custom

Name SiteA

Name SiteB

Name SiteC

Dial-peer cor list SiteA

Member SiteA

Exit

Dial-peer cor list SiteB

Member SiteB

Exit

Dial-peer cor list SiteC

Member SiteC

5.       Assuming that the calling number at Site A is 5XXX, Site B is 6XXX and Site C is 7XXX, we set up the incoming dial peers as follows:

Dial-peer voice 100 voip

Answer-address 5…

Corlist incoming SiteA

dial-peer voice 200 voip

answer-address 6…

corlist incoming SiteB

dial-peer voice 300 voip

answer-address 7…

corlist incoming SiteC

This ensures that the incoming dial peer chosen for Site A is always Dial-peer 100, for Site B it is 200 and for Site C 300.

6.       We now set up the outbound calls as follows (dial peers will need to be created according to the numbering plan):

Dial-peer voice 1 pots

Trunkgroup SiteA

Destination-pattern 9T

Corlist outgoing SiteA

Dial-peer voice 2 pots

Trunkgroup SiteB

Destination-pattern 9T

Corlist outgoing SiteB

Dial-peer voice 3 pots

Trunkgroup SiteC

Destination-pattern 9T

Corlist outgoing SiteC

This should ensure that Site A uses dial-peer 1 for outgoing calls via the cor list configuration. It will not have access to the other dial peers. Dial peer 1 has a trunk group of SiteA which includes channels 1-8 of the PRI. Similarly for the rest of the Sites.

Have you (or anyone else out there) ever seen this done?

Thanks,

Debbie

asandborgh Tue, 01/12/2010 - 18:37

Debbie,

This is the solution that Paolo referred to earlier, but did not detail (I had NO idea).  After he responded I inquired on the side and he showed me a similar config, although with reservations.  If I were you I would solicit his wise advice on dealing with the Telco and the ongoing supportability of the solution.

Paolo?

HTH,

Art

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