“Cloud PBX” is practically the same as the telephone system, only it
works within the Internet means, not the simple telephone line. Using this
service you don’t have to worry about how flexible and reliable is your
telephone system anymore.
Gatekeeper is an administrational tool for H.232 multimedia networks. A single unit can control interactions for each zone, which comprises the terminals, MCU's and gateway within the frames of a particular domain. Gatekeeper is an optional element, but when it available, it becomes the central administrative entity.