Gateways, Gatekeepers and Softswitches Media gateways, gatekeepers and softswitches are all components of a hybrid PSTN and IP networks, and they can run the gamut of protocols. Consistent support of protocols in these various network components are what enable a hybrid network to operate seamlessly end to end with consistent services, features and reliability. The media gateway translates the lower layer transport protocols from one network to another. There are very few media gateways deployed from all vendors, according to Byars, who says that this is one reason for the dearth of IP telephony services to date. The gatekeeper can function as a virtual switch and translate phone numbers to IP addresses.
Endpoints register with the gatekeeper and request permission to place a call to another endpoint.
If granted, the gatekeeper returns the transport address for the call signaling channel of the called endpoint. Some vendors' softswitches support multiple voice signaling protocols to allow a single device to simultaneously speak to several gateways that interface with networks with varying signaling needs. This flexibility enables the integration of voice and data protocols, and of existing PSTN signaling interfaces for smooth migration of existing services. MGCP, H.248 and Megaco Media gateway controllers and media gateways must run certain protocols to control media flows. These protocols control IP telephony gateways from external call elements.