Legacy PBX and SIP Trunk

[Ajay Singh]

Hi,

One of our customer needs SIP trunking services. Cuurently they have 3 different Legacy TDM PBXs & is willing to use existing PBXs rather than moving to IP PBX. How can we acheive this?

Option 1: TDM PBX ---->QSIG--->Cisco ISRG2 Gateway (H.323) ----> SIP -----> SIP Service provider network

Option 2: TDM PBX ---->QSIG---> H.323 On Cisco ISRG2 Gateway ----> SIP on CUBE (same ISRG2 running H.323 GW) ---> SIP Service provider network

Which option is suitable???

As far as i know, Option 1 will suffice since there is no IP PBX and TDM doesn't understand IP so gateway will take care of everything and CUBE licenses are not needed. QSIG --> H.323 --->SIP signal conversion and transcoding can be taken care by gateways itself.

Is my understanding correct and we can go with Option1 or not?? What other consideration needs to be taken or we should go with Option 2??

Secondly if i am choosing option 2 and running CUBE & Gateway both on same router, do i need to consider CPU utilization also. E.g. Cisco 2901 supports 100 SIP sesions and if i need TDM - IP conversion also for 80 sessions, will there be any effect on CPU utilization or i just need to put CUBE licenses and CPU utilization will not have a considerable impact.

I was going through the Gateway section of SRND but i found the information a bit ambigutous to conclude for solution

[chuck.brule · Accepted solution]

You don't need H323 at all in this setup, man.

The Correct Setup Is:

TDM PBX ----PRI--->Cisco ISRG2 Gateway with PVDMs and VWIC2 or better ----SIP-----> SIPSP

This works like you have a PRI gateway from the PSTN to CUCM, except reversed. The VOIP call legs face your SIP SP, and the POTS call legs face the PBX.

I'd recommend against Q.SIG. I know a lot of people like it but each PBX vendor speaks a slightly different version and it gets messy. Just provision the whole thing as NI2 and make sure you are the network and clock source for the PBX (clock source internal on the controller and protocol-emulate network on the Serial x/x/x:23 interface).

Make sure your dial peers are set up correctly and this is easy as cake, man.

Let me know if you need any configuration assistance on this, I've done it like a thousand times.

Chuck

[raymond00]

Chuck's PRI suggestion is great. Just to add to it, don't forget to use a T1 crossover cable between the PBX and ISR when emulating a PRI.