Cambridge O Level Computer Science · Syllabus 2210 · Data Transmission
Router
What is Router?
A router is a network device that reads the destination address in a packet's header and controls the route the packet takes, forwarding it onward towards its destination.
This definition is part of the Data Transmission chapter in Cambridge O Level Computer Science.
Router in context
Every idea in Topic 2 sits somewhere on one journey. Data has to travel; it is divided into packets so that many users can share the same network; routers choose a route for each packet independently; the method of transmission (how the bits travel and in which directions) is chosen to suit the situation; interference on the way can corrupt the data; an error-detection method reveals that corruption; automatic repeat query asks for the damaged data again; and encryption keeps the contents private from anyone who intercepts them on the way. Learn the chapter as that single chain and every individual method has an obvious place to hang.
Packet switching is a method of transmitting data in which the data is broken down into packets and each packet is sent across the network independently. A router controls the route a packet takes, so each packet could take a different route from the same sender to the same receiver. Because the routes can differ in length and congestion, packets may arrive out of order. Once the last packet has arrived, the packets are reordered using the packet numbers in their headers, and the original data is reconstructed.
Questions students ask about Router
Why is data broken down into packets before it is transmitted across a network?
Splitting data into packets means many users can share the same network instead of one transfer occupying the link from start to finish, means each packet can be routed independently by a router, and means a single damaged packet can be dealt with on its own rather than resending the whole file. Each packet carries a header with the destination address, packet number and originator's address, a payload, and a trailer, so the receiver can reorder and rebuild the original data once every packet has arrived.