Networks, topologies and protocols · GCSE Computer Science

Types of network

A network is two or more devices connected so they can share data and resources.
A LAN (local area network) covers a small area, such as a school, and its hardware is usually owned by the organisation. A WAN (wide area network) covers a large area, often using links hired from telecoms companies. The internet is the biggest WAN. (AQA) A PAN (personal area network) connects devices around one person, such as Bluetooth earphones.
Wired connections (copper or fibre-optic cables) are faster, more reliable and more secure. Wireless connections (Wi-Fi) let devices move around, but are slower and can suffer interference.

A network interface controller (NIC) connects a device to a network. A switch connects the devices in a LAN and sends data to the right one. A router connects different networks, such as a LAN and the internet, and directs packets between them. A wireless access point lets devices join by Wi-Fi.
Client–server: servers provide services, such as files or web pages, to clients. It is easier to manage and back up, but the server is expensive, and if it fails the clients lose access.
Peer-to-peer: every computer is equal and shares with the others. It is cheap and simple, but harder to manage and back up.

Star: every device connects to a central switch. If one cable fails, only that device is affected, but if the switch fails, the whole network stops. It needs a lot of cable.
Bus (AQA): all devices share one main cable. It is cheap, but data collisions slow it down as more devices join, and a break in the main cable stops the network.
Mesh (OCR): each device connects to several others, so data can take many routes. It is very reliable, but expensive.

A protocol is a set of rules for communication. Data is split into packets, which may take different routes and are put back together at the end.
TCP splits data into packets and checks they all arrive. IP addresses and routes the packets. UDP sends packets without checking, which is faster (good for live streaming). HTTP and HTTPS fetch web pages (HTTPS is encrypted). FTP transfers files. SMTP sends email. IMAP and POP receive email: IMAP keeps it on the server, while POP downloads it.
Ethernet and Wi-Fi are standards for wired and wireless LANs.
Protocols are organised into layers, each doing one job. (AQA) The TCP/IP model has four layers: application, transport, internet and link.

An IP address identifies a device on the internet. A MAC address identifies a piece of network hardware. DNS (the domain name system) translates domain names, such as example.com, into IP addresses.
Performance depends on bandwidth, the number of users, the type of connection, interference and distance.

LAN: A local area network, covering a small area such as a school.
WAN: A wide area network, covering a large geographical area.
Router: A device that connects different networks and directs packets between them.
Switch: A device that connects the devices in a LAN and sends data to the right one.
Protocol: A set of rules for how devices communicate.
Packet: A small piece of data sent across a network.
Star topology: A network layout where every device connects to a central switch.
IP address: A number that identifies a device on the internet.
MAC address: A unique address given to a piece of network hardware.
DNS: The domain name system, which translates domain names into IP addresses.