You mean that i must double my PRI lines to do this migration ? Let me me ask you if i understand your solution:

         CUCM-----QSIG/H323/MGCP router-------PBX------------1st PRI Line------------>PSTN

             |

             |

             |

             !

      MGCP Router

             |

             |

             | Other PRI Line to avoid overload on QSIG Trunk

             |

             !

         PSTN

This is the solution you used to migrate ? I have 20 PRI lines on PBX: can i setup 1 QSIG trunk for every PRI ?

I wouldnt say double.....     Let me see if I can explain this:

For example, I have 2,000 DNs on my Nortel PBX.  Approx call volume through PSTN is around 1 channel per 10 DNs.

If i were to migrate 100 DNs to the CUCM, Im looking at approx 10 channels for PSTN connectivity and then misc station to station calls.

To provide connectivty, I need to have (1) QSIG T1 between CUCM and Nortel to make this work and still have bandwidth.

On the CUCM, I install a new PRI on a new router. (Say MGCP).   When my CUCM callers make an outside call, they will use this PRI.  But all incoming calls will still come from the Nortel via the QSIG trunk.

If your PSTN Carrier will allow you to break up the DID Banks and migrate them to the new PRI, even better!  Most carriers are starting to allow the breaking of DID banks between PRI groups.  So for example, I had the range 555-1000-1999.   But I was moving DID numbers 1050, 1060, 1061, 1072 to the new PRI.  Most will allow it.  Some do not.. all depends.

At some point though, you will have more phones and DNs than on the Nortel, at this point, you should move all the PRIs over to the CUCM and route traffic *back* to the Nortel as needed.  For example, I had 1200 DIDs on the CUCM (phones) and 800 on the Nortel, it would make more sense to move all PRI traffic to the CUCM and push traffic back through the QSIG as needed.

The trick here to balance the trunk between CUCM and Nortel, and also the PSTN traffic incoming/outgoing. 

You will also need to figure out voicemail.   I typically do (and Cisco recommendeds) you migrate everyone to a common voicemail platform FIRST, before turning up phones.  This way, whether they are on CUCM or Nortel, the voicemail is the same.  If you have (2) different voicemail platforms, then you have to deal with AMIS or VPIM or?  But all depends on the scenario, budget, business drivers, etc... you may have to use AMIS or VPIM if required.

Hope I have not confused you.

In the end, you will probably pay a little more for PRIs than you would hope to be paying, but it will help your migration.  Those costs assocaited to the "double PRIs" will only be temporary.

Hey Tommer,

Great answer my friend! Worthy of 5 points for sure

We used the method given by Tommer for our Notel to CUCM migration, and used DSC's

(Distant Steering Codes) on the Nortel side to route incoming calls to DN's that had moved over

to CUCM. Worked sweet!

Cheers!

Huff

Thank you,

your explanation was clear about how QSIG channel can go busy when overloading it with additional calls. But consider my migration architecture showed below: (i have an MGCP router with a 2 port VWIC2-2MFT: one connected to PSTN and the other for QSIG Trunk connected to Nortel)

                                                                                                                        IP

PSTN----------to 1st port of VWIC2-2MFT---------> MGCP Router--------------> CUCM--------> Cisco DN's

                                                                                                         |

                                                                                                         |
                                                                                                         | (QSIG on 2nd port of  VWIC2-2MFT)

                                                                                                         |

                                                                                                         |

                                                                                                   Nortel PBX

                                                                                                         |
                                                                                                         |

                                                                                                         |

                                                                                                         |

                                                                                                  Nortel DN's

I have calls going into QSIG channel in these 4 situations: (Cisco DN's are Phones migrated to CUCM and Nortel DN's are Phones not yet migrated)

1.   Cisco DN's to Nortel DN's

2.   Nortel DN's to Cisco DN's

3.   Nortel DN's to PSTN

4.   Voicemail channels

So, it's true that i can overload the QSIG channel because of additional station to station calls but not for "Cisco DN's to PSTN" calls. Consider that i have 6 MGCP routers with 18 VWIC2-2MFT cards, so i must set up many QSIG channels as possible.

So, my final questions are:

1.    Do you think my migration architecture  (with special handling of QSIG congestion) can work ?

2.    have you got a link to any documentation about configuring CUCM and MGCP router for my migration architecture ? (i read every documentation about it, but all are dealing with this type of architecture: PSTN------->PBX---------->MGCP Router---------->CUCM and not with mine that is a little bit different)

Thank you and Good Luck to Packers!!!!