Gateway

Gateway is a piece of networking hardware used in telecommunications for telecommunications networks that allows data to flow from one discrete network to another. Gateways are distinct from routers or switches in that they communicate using more than one protocol to connect multiple networks and can operate at any of the seven layers of the open systems interconnection model (OSI).

NENA-STA-010, Detailed Functional and Interface Standards for the NENA i3 Solution

Wikipedia definition