Whats the difference between a Gateway & Gatekeeper?

I am new to asterisk and the telecom/networking side of computer science. i need to know the difference between a gatekeeper and a gateway. i know a little about the gateway which we r using with asterisk to route the call from pstn to asterisk server. but i dont know anything about gatekeeper. are these different names for a single thing?

If u know about any article on this topic plz mention


Gateway = pathway between two different networks. IE: A TDM->IP gateway allows you to bridge calls between the PSTN and an IP network.

Gatekeeper = a device that controls access to a network. IE: an H.323 gatekeeper allows devices like phones to register with an IP network and use it. Just like a SIP proxy/registrar service.

thanx for the reply. the basic concept is clear. if u know any article on this topic plz share