Trunk from CUCM to ITSP

[mumbles202]

Is it still not recommended to have a trunk directly from CUCM to a carrier?  Currently have 1 carrier configured via a pair of 4331s in a redundancy group.  A new carrier is coming in and they plan to terminate a sip trunk on their equipment and then have an interface on our internal network on the same segment as CUCM.  Would there be any disadvantage to configuring a trunk from CUCM directly to their internal address, similar to as if it were a different 4331?  

[Roger Kallberg]

Yes it’s not recommended. Primarily because you’re going to open up your entire network to the service provider as each internal endpoint that is involved in any call would send and receive traffic to/from the service provider equipment. Apart from that can you provide a little more information on what you mean by “they plan to terminate a sip trunk on their equipment”? Do you mean that it will serve as an SBC or do you mean something else?

[mumbles202]

Thanks for the reply. Yes, they'll have a SBC onsite.

I've always used a VG in path between carrier and CUCM but thought I'd ask. 

[Roger Kallberg · Accepted solution]

The router in-between the CM and the carrier is acting as an SBC, not really the same as a VG. Anyway not how the term VG is typically used. A SBC acts as a demarcation point between the different networks and connects the VoIP call legs together from the networks.

If the service provider CPE acts as a SBC you technically may not have a direct need for an SBC between, but you should know that without it you’re vulnerable to intrusion via the SP network. I would never recommend such a solution.

[mumbles202]

Thanks for the reply. I usually use VG to refer to the device sitting between CUCM and the carrier, whether it be a CUBE or has a PRI, but your point is well taken. 

I'll recommend sticking with the CUBE inline with the carrier equipment.