Networks: who talks to whom
A network joins computers so that they can share data and devices. A LAN (local area network) covers one building, such as a school. A WAN (wide area network) covers a large area and links LANs together; the internet is the biggest WAN. A router passes data between networks and chooses the way. A hub is simpler: it repeats whatever it receives to every connected device. In a client-server system a server holds a service or data (files, web pages, mail) and clients ask for it. In a peer-to-peer system all computers are equal and share with each other, with no central server. How does a message cross a network? With circuit switching, as in the old telephone system, a line is reserved for the whole call: the quality is steady, but the line is wasted when nobody speaks. With packet switching, used by the internet, the message is cut into small packets. Each has a number and an address and may travel its own way, and the receiver puts them together by number. It uses the lines efficiently, though packets can arrive in a different order.
| Packet number | Content | Arrives |
|---|---|---|
| 1 | line 1 | second |
| 2 | line 2 | first |
| 3 | line 3 | third |
| Circuit switching | Packet switching | |
|---|---|---|
| Line | reserved for the whole call | shared by many messages |
| Quality | steady | can vary |
| Efficiency | wasteful when silent | efficient |
| Order | always in order | may change; rebuilt by numbers |
Draw the network of your school computer room: where is the router, which computer could be the server, how are the clients connected? Then say whether it is a LAN or a WAN, and what you would need to join it to another school’s network.