A network connects devices so they can share data and resources. This topic covers the kinds of network, how they are connected, and the rules that let different devices communicate.
A network is two or more devices connected so they can exchange data and share resources such as files, printers and an internet connection.
The costs are the hardware and management involved, and the risk that a fault or an attack affects many devices at once. A client-server network puts shared services on dedicated servers.
A LAN covers one site and is usually owned by the organisation using it.
A WAN spans a wide geographic area and relies on infrastructure the organisation does not own. The internet is the largest example. A PAN covers a few metres around one person, typically over Bluetooth.
Wired connections are generally faster, more reliable and harder to intercept.
Wireless connections allow movement and need no cabling, but range is limited, and walls and other signals can interfere. Fibre optic cable carries data as pulses of light, giving high speed over long distances.
A star topology connects every device to a central switch. One failed cable affects only its own device, but a failed switch stops the whole network.
A mesh topology connects devices to several others, so data can take another route if one link fails. A bus topology shares a single backbone cable.
Bandwidth is the maximum rate at which data can be carried. Latency is the delay before data arrives.
Performance also depends on how many devices are active, the transmission medium, and interference. Packet loss means some packets never arrive and have to be sent again.
Network speed is measured in bits per second, and in multiples: kilobits, megabits and gigabits per second. Note that speeds use bits while file sizes use bytes.
A network interface card lets a device connect to a network. A switch connects devices within a LAN and sends data only to the device it is meant for.
A MAC address is a fixed hardware address given to each network interface.
An IP address identifies a device’s location on a network. IPv4 addresses are 32 bits long.
A router forwards packets between different networks, choosing a route towards the destination.
A protocol is an agreed set of rules for communication, so devices from different makers can work together.
Protocols are organised into layers, each with its own job: application, transport, internet and link. A layer can be changed without rewriting the others.
Data is split into packets, each addressed separately, which may take different routes and are reassembled at the destination.
Data crossing a network can be read by anyone able to intercept it. Encryption scrambles it so that intercepted data is unreadable without the key.
HTTPS encrypts web traffic, and modern Wi-Fi encrypts wireless traffic.
