Cisco CUBE and SIP Trunks

SIP trunking is becoming more common place nowadays so here is a little post containing information and some specific references to CUBE - The Cisco Unified Border Element.

First off SIP trunks can be used for a number of different applications but a popular use, and the one I'm describing here, is to replace traditional connectivity to the PSTN. A SIP trunk can be provided by a ITSP (Internet Telephony Service Provider), the ITSP then provides the connection to the PSTN. The primary advantages are cost and scalability, a SIP trunk often connects over Ethernet (Gigabit or Fast Ethernet) and so has a much higher scalability for calls compared to traditional circuits.

The 3 basic components would be
1) The SIP Trunk from the ITSP
2) A Border Element which is essentially a gateway between the IP PBX and the ITSP
3) A PBX, IP or Otherwise

In a Cisco environment element 2 is a router with CUBE licensing on it, often just referred to as a CUBE. A CUBE router requires the relevant UC licenses, such as the UC package license for the ISRG2's, DSPs for translating between calls with different codecs, CUBE licenses and appropriate interface, most commonly Ethernet but check with the ITSP.

CUBE Licenses are cumulative and licensed based on a number of sessions. An example is:
FL-CUBE-25

CUBE is defined as an IPIPGW (i.e. H.323-SIP, SIP-SIP or H.323-H.323 dial-peer connections, using the "voice service voip > allow-connections" CLI). Gatekeeper is defined as the H.323 GK functionality (and "gatekeeper" CLI). Meaning the SIP trunk to Provider network requires a CUBE license.

You do not need a CUBE license for a SIP trunk built directly between CUCM clusters. For example:
|<-----------------------signaling--------------------------------->|
IP Phone----CUCM Cluster 1-----------IP WAN--------------------CUCM Cluster 2-----TDM GW--------External Phone

You do need a SIP trunk license when you use a gateway to terminate the CUCM signalling (and often media as well) and re-generate the signalling to the SIP trunk provider or third party PBX. For example:
|<---signaling--------->|<-----------signaling---------->|
IP Phone-----CUCM Cluster------------------29xxGW-----------------------SIP provider/third party IP PBX-------External Phone 


References:
What is SIP Trunking?
http://www.siptrunk.org/whatissiptrunking.php

CUBE FAQ (2011)
https://supportforums.cisco.com/docs/DOC-17964

CUBE v8.8 datasheet
http://www.cisco.com/en/US/prod/collateral/voicesw/ps6790/gatecont/ps5640/product_data_sheet09186a00801da698.html