A router (also known as a packet switch) is a device that is used to interconnect two or more networks. Its function will be discussed in more detail in Level 2 of your course, but in outline a router is is responsible for forwarding a packet (datagram) from a link in network to a link in another network. The path taken by a packet from end-system to another end-system, is known as a route. Routers, are responsible for moving packets closer to their destination and in this sense they work like the post-office sorting offices that are used to deliver mail items. Each packet in the Internet has a source and destination IP address which are used by the routers in their forwarding role.

The incoming and outgoing links to a router need not use the same link protocol: for example, if you have a WiFi router at home, then your PC connects to the home network by wireless, but the router probably connects to the your broadband modem by Ethernet.

Routers are “Network Layer” devices and they implement the routing part of the Internet Protocol. Routers are points of possible network congestion and if packets arrive at a faster rate then the outgoing links, they will need to queue. If the queue is overloaded, packets can be lost. See also: Internet Protocol, Network Layer, Store and Forward, Queuing Delay, Transmission Delay, Processing Delay.

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