Describe network topologies, network types and transmission media, and compare transmission methods used to carry data between devices

What this dot point is asking

NESA wants you to describe how computer networks are arranged and how data physically travels between devices. You need network types (LAN, WAN), topologies (star, bus, ring, mesh), transmission media (twisted pair, coaxial, fibre, wireless), and the concepts of bandwidth and transmission method, with the ability to compare options for a given situation.

The answer

Why networks matter

Networks make the transmitting and receiving information process possible across distance, letting many users share data, storage, printers and internet access. Almost every system you study (transaction processing, decision support, multimedia) depends on a network to move data between its parts. The syllabus asks you to compare networking choices, so a strong answer weighs options rather than describing one.

Network types

• A local area network (LAN) connects devices within a small geographic area, such as a single office, school or building. It uses cabling or wireless that the organisation owns and controls, and offers high speed at low cost over short distances.
• A wide area network (WAN) connects devices over large distances, often linking many LANs across cities or countries. WANs typically use telecommunications carriers and the internet, trading lower speed and higher cost for reach.
• A personal area network and a metropolitan area network sit at the small and city scales respectively.

Network topologies

Topology is the physical or logical arrangement of devices on a network.

• Star: every device connects to a central node (a hub or switch). It is easy to manage and one cable fault isolates a single device, but the central node is a single point of failure.
• Bus: all devices share one common backbone cable. It uses little cabling but a break in the backbone can disable the whole network, and heavy traffic causes collisions.
• Ring: devices form a closed loop and data passes from one to the next. Performance is predictable, but a single break can interrupt the loop unless it is dual-ring.
• Mesh: devices interconnect with many paths, so if one link fails data is rerouted. Mesh is highly reliable but uses the most cabling, which is why it suits critical backbones and wireless mesh networks.

Transmission media

The medium is the physical path the signal travels.

• Twisted pair copper cable is cheap and common for LANs but limited in distance and prone to interference.
• Coaxial cable carries higher frequencies over longer distances with more shielding.
• Fibre optic cable carries light through glass, giving very high bandwidth, long distance and immunity to electrical interference, at higher cost.
• Wireless media include radio (Wi-Fi), microwave (line of sight links) and satellite (very long distance with noticeable delay). Wireless trades convenience and mobility for lower security and more interference.

Bandwidth and data transfer

Bandwidth is the amount of data a channel can carry per second, measured in bits per second. Higher bandwidth allows faster transfer and more simultaneous users. Throughput is the actual data rate achieved, which is lower than the raw bandwidth because of overheads, errors and congestion. Latency, the delay before data starts arriving, also affects how responsive a network feels, and is high on satellite links.

Switching and devices

Networks use devices to move data: a switch forwards data only to the device it is addressed to within a LAN, a router directs packets between networks, and a modem converts between digital data and the signal a carrier line uses. Packet switching breaks data into packets that travel independently and are reassembled, which uses the network efficiently and underlies the internet.