An IP-to-IP gateway is a separate router that provides a proxy (or front end) for a system that does not support H.450, such as Cisco Unified CallManager. The IP-to-IP gateway can be placed between Cisco Unified CallManager and a CME router, and it provides H.323-to-H.323 call connections to terminate and re-originate calls for transfers and forwards to endpoints that do not support H.450.

Cisco Unified CallManager Express can be directly integrated with Cisco Unified CallManager using an H.323 interface without the IP-to-IP gateway. However, because Cisco Unified CallManager does not support H.450 specifications, supplementary services such call transfer and call forward initiated from Cisco Unified CallManager phones will require the media to be hair-pinned (over the WAN in some cases) through Cisco Unified CallManager even though the Cisco Unified CallManager phones might not be involved in the call. The IP-to-IP gateway ensure that this media hair-pinning does not occur over the WAN.

The IP-to-IP gateway can also act as the PSTN gateway for the remote Cisco CME systems as well as for Cisco Unified CallManager. A separate PSTN gateway is not required in such cases.

The IP-to-IP gateway must run a Cisco IOS release that is compliant with Cisco CME 3.4 and that supports H.450, such as Cisco IOS Release 12.4(6)T or later with the IP VOICE feature set.

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