Quick Tech Tip: InterNetworking

What are we talking about ? The interconnection of two or more networks, usually local area networks so that data can pass between hosts on the different networks as though they were one network. This requires some kind of router or gateway to facilitate the process of interconnecting two or more individual networks to facilitate communications among their respective nodes. Note: The interconnected networks may be different types. Each network is distinct, with its own addresses, internal protocols, access methods, and administration.
For different networks to interact, devices such as repeaters, bridges, routers, gateways are required. Repeaters are low level devices that just amplify or regenerate weak signals. They are needed to provide current to drive long cables. They copy individual bits between cable segments.
Unlike repeaters, bridges are store and forward devices. A bridge accepts the whole frame and passes it to the data link layer where the checksum is verified. Then the frame is sent down to the physical layer for forwarding on a different network.
Multiprotocol routers are conceptually similar to bridges, except that they are found in the network layer. They take incoming packets from one line to another, just as all routers do, but the lines may belong to different networks and use different protocols.
Transport gateways connect byte streams in the transport layer. Application gateways connects two parts of an application in the application layer.
When a gateway is between two WANs run by different organizations in different countries, the gateway is ripped apart in the middle and the two parts are connected with a wire.