SIP Gateway & ISDN PRI Configuration

[C_Noble]

I am trying to clear up some confusion on my understanding of SIP voice gateways.

I have a 2900 series router at a customer site that is currently configured for MGCP with a T1 PRI.
The MGCP and T1 are functional.

Is it possible to utilize a SIP trunk from CUCM to the router instead of using MGCP?

Where can I find an an example configuration for the above?

[b.winter]

Yes, you can. Why should you not? Why are people are so confused when changing to SIP?
The protocol between CUCM and the VGW in general has nothing to do with the connection you have from VGW to PSTN or somewhere else (Yes, I know, MGCP is special in that way).

You could have x combinations:
H.323 <--> VGW <--> E1/T1
SIP <--> VGW <--> E1/T1
SIP <--> VGW <--> SIP
SIP <--> VGW <--> H.323
...

I bet you will find many posts here in the forum.

[C_Noble]

Ok so my confusion is on the SIP portion of the configuration.

I understand that the command "sip-server" can be used in a VoIP Dial Peer configuration as "session target sip-server".
I also understand that "sip-server" would be the Call Manager.

That being said what is the command "registrar" used for?

Router(config)#sip-ua
Router(config)#registrar CALL MANAGER IP
Router(config)#sip-server CALL MANAGER IP

Router(config-dial-peer)#session protocol sipv2
Router(config-dial-peer)#session target sip-server

Thanks in advance

[b.winter · Accepted solution]

"sip-server" only applies, if you have it configured in a tenant or in the sip-ua section. So, to point to CUCM in the DP, I would either user "session target ipv4..." or "session server-group <nr>".
In a "session server-group" you can define multiple IPs/FQDNs. Otherwise you would have to add one DP per destination (multiple CUCM nodes, like in the past with old IOSs without that feature of session server-groups).

sip-ua is a section for general SIP config. Normally, sip-ua isn't needed at all.
In the past (before the tenant feature was available) the SIP trunk registration was configured there. But nowadays the "current" config standard for SIP Trunk registration is to use tenants.

This said, in your case you don't need any registration, because the VGW doesn't register to CUCM. It's just a SIP trunk (connection) between them. Therefore, you don't need the command "registrar".

[Scott Leport]

Hi,

As @b.winter says, you can do that, but why would you want to? What are you looking to achieve? 

It's generally better practice (and simpler) to use the same protocol throughout where possible. Much easier to troubleshoot when things go wrong. 

[C_Noble]

Thank you guys!