Part A: Foundations
Data communication and networks overview
Key takeaways
- Networks exist to let separate devices share data, applications and hardware resources, enabling collaboration, centralised data management and communication at a scale and speed no standalone device could achieve.
- By scope, a PAN covers a few metres around one person, a LAN a single building or campus, a MAN a city, and a WAN a country or a global span.
- A workgroup is a peer-to-peer group with no central authority, each machine managing its own accounts; a domain is centrally managed by a domain controller that authenticates users and enforces policy, and suits larger, more secure environments.
- Simplex sends in one direction only (a broadcast radio signal), half-duplex in both directions but one at a time (a walkie-talkie), and full-duplex in both directions at once (a telephone call).
- Digital transmission is a discrete binary signal, more resistant to noise and easier to process, encrypt and compress than a continuously varying analog signal; wireless transmission trades the convenience of no cabling for greater exposure to interference and interception.
This paper moves from CISSE's earlier, lighter treatment of networking into a full design-and-administer discipline. This opening chapter fixes why networks exist, what services they provide, how they are classified, and the basic modes data can travel in.
Why networks exist
Networks exist to let separate devices share data, applications and hardware resources, enabling collaboration, centralised data management, and communication at a scale and speed no standalone device could achieve alone.
Network services
- File sharing and storage
- Print and resource sharing
- Email and messaging
- Web hosting and access
- Authentication and directory services (see Domains and workgroups, below)
Network types
| Type | Scope |
|---|---|
| PAN (Personal Area Network) | A few metres, around one person |
| LAN (Local Area Network) | A single building or campus |
| MAN (Metropolitan Area Network) | A city |
| WAN (Wide Area Network) | A country or global span (see the chapter on WANs) |
Domains and workgroups
Self-check
(a) State three services a network provides. (3 marks)
(b) Distinguish a LAN from a WAN by scope. (2 marks)
(c) Distinguish a workgroup from a domain, stating which suits a large, security-conscious organisation. (3 marks)
Show worked answer
(a) Any three of: file sharing and storage; print and resource sharing; email and messaging; web hosting and access; authentication and directory services.
(b) A LAN covers a single building or campus. A WAN spans a country or global distance.
(c) A workgroup is a peer-to-peer group of computers sharing resources with no central authority, each machine managing its own accounts. A domain is centrally managed, a server (domain controller) authenticates users and enforces policy across every joined device. A domain suits a large, security-conscious organisation.
Transmission modes
| Mode | Direction |
|---|---|
| Simplex | One direction only, e.g. a broadcast radio signal |
| Half-duplex | Both directions, but only one at a time, e.g. a walkie-talkie |
| Full-duplex | Both directions simultaneously, e.g. a telephone call |
Digital and analogue transmission
Wireless transmission
Wireless transmission carries signals through the air rather than a physical cable, using radio waves (Wi-Fi, cellular), microwave (point-to-point links) or infrared (very short range), trading the convenience of no cabling against greater exposure to interference and interception, addressed directly in the wireless LAN chapter's threats and authentication sections.
Exam tip
The transmission modes above are frequently tested by matching a described real-world communication method to the correct mode, a walkie-talkie's "press to talk" behaviour is the clearest half-duplex example to anchor the definition to.
Self-check
(a) State the three data transmission modes, with an example of each. (6 marks)
(b) Distinguish analog transmission from digital transmission. (3 marks)
(c) State two trade-offs of wireless transmission compared to a physical cable. (2 marks)
Show worked answer
(a) Simplex, one direction only, e.g. a broadcast radio signal. Half-duplex, both directions but only one at a time, e.g. a walkie-talkie. Full-duplex, both directions simultaneously, e.g. a telephone call.
(b) Analog transmission is a continuously varying signal, e.g. traditional voice telephony. Digital transmission is a discrete, binary (0/1) signal, more resistant to noise and easier to process, encrypt and compress than analog.
(c) Any two of: no cabling required, giving convenience and mobility; greater exposure to interference; greater exposure to interception, requiring dedicated wireless security measures.