Gateway/Router:
To connect a TCP/IP local-area-network to another TCP/IP LAN or via a Wide-Area-Network (WAN), you need a device known as Gateway or Router, which is a communications device/program, which passes data between networks having similar functions but dissimilar implementations. A router is a layer 3 (network layer) gateway and a mail gateway is a layer 7 (application layer) gateway.
A gateway is often associated with both a router, which directs the packets of data that arrive at the gateway, and a switch, which furnishes the path in and out of the gateway for a given packet.
Gateway devices are commonly divided into the following three functional categories, or any combination of these three:
Data Gateway.
Multimedia Gateway.
Home Control Gateway.
