Just to elaborate on the response as to why a single gatekeeper would be the correct way to go.
The gatekeeper just provides a consolidation of VoIP call routing configuration on one box that would otherwise have to reside on every one of your gateways.
The dial-peers on the originating side of a VoIP call are set up to consult the gatekeeper rather than having a fixed IP address set as the target for the call.
The idea would seem to be to reduce the amount of configuration on the gateways so that required changes can be effected on just one central box. I think that the system also responds better to a gateway going down since the gateway is supposed to send keepalives to the gatekeeper while it is up and available.
The fact that you still have to define all sorts of information ( like codec, fax rate, DTMF relay protocol ) in the dial-peers on the gateway, means that the gatekeeper solution is not as useful as it might be.
I haven't tried it, but I guess if you try to design a dial plan with your own custom prefixes you can keep the dial-peer on your gateways down.
By this I mean that you might prefix all E.164 numbers with '7' say, and just have a single dial-peer for destination-pattern '7T' on your gateways.
This assumes that you have no desire to use different dial-peer parameters between different destinations.
On your gatekeeper you can have separate entries for every E.164 prefix you want to handle in a distinct way ( 7-44 for UK, 7-1-561 if you happen to have a gateway in that area code ... ).
In a similar way you could use a 9 prefix for some kind of internal dial plan for interfacing into a network of company PBXs, and have just a single '9.......' voip dial-peer per gateway.
Like I say, this is all hypothetical, but it's the only way I can think of that makes a gatekeeper efficient in terms of a configuration maintenance reduction device.
