Last reviewed 16 Sept 2026 · 11 min read
Data communication
Data communication — exchange of data between devices via a transmission medium.
Components
- Message (data), 2. Sender, 3. Receiver, 4. Transmission medium, 5. Protocol (rules).
Transmission modes (direction)
| Mode | Direction | Examples |
|---|---|---|
| Simplex | One direction only | Keyboard to computer, TV/radio broadcasting |
| Half-duplex | Both directions, one at a time | Walkie-talkie |
| Full-duplex | Both directions simultaneously | Telephone, mobile calls, modern Ethernet |
Other transmission concepts
- Serial (one bit at a time — USB, long distances) vs parallel (several bits simultaneously — short distances).
- Asynchronous (start/stop bits per character) vs synchronous (clock-synchronised blocks).
- Bandwidth — range of frequencies (Hz) / data capacity; data rate in bits per second (bps, kbps, Mbps, Gbps).
- Latency — delay; throughput — actual rate achieved.
Transmission media
Guided (wired) media
| Medium | Features | Uses |
|---|---|---|
| Twisted pair cable — UTP/STP (Cat 5e, Cat 6, Cat 6A) | Pairs twisted to reduce interference; cheap; distance limited (≈ 100 m per Ethernet segment) | LANs, telephone lines |
| Coaxial cable | Central conductor, insulation, braided shield; better shielding | Cable TV, older networks |
| Optical fibre | Light pulses; very high bandwidth, low loss, immune to EMI, secure | Backbone networks, FTTH, undersea cables, long distances |
Unguided (wireless) media
| Medium | Features / uses |
|---|---|
| Radio waves | Omnidirectional; FM radio, Wi-Fi, mobile networks |
| Microwaves | Line-of-sight; terrestrial microwave links, satellite, mobile backhaul |
| Satellite communication | Wide coverage; TV broadcasting, VSAT, GPS; propagation delay |
| Infrared | Short range, line of sight; TV remotes |
| Bluetooth | Short range personal area networks (headsets, file transfer) |
| Wi-Fi (IEEE 802.11) | Wireless LAN |
Computer networks
A network — interconnected computers and devices sharing resources (files, printers, internet) and communicating.
Advantages
Resource sharing, communication (email, messaging), centralised data management and backup, collaboration, cost saving, remote access.
Types by area
| Type | Coverage | Examples |
|---|---|---|
| PAN (Personal Area Network) | A few metres around a person | Bluetooth devices, smartphone hotspot |
| LAN (Local Area Network) | Room, building, campus | Office network, computer lab |
| CAN (Campus Area Network) | Interconnected LANs in a campus | University campus |
| MAN (Metropolitan Area Network) | City | City-wide cable/fibre networks |
| WAN (Wide Area Network) | Country/continents | The Internet (largest WAN), bank networks |
Architecture
- Peer-to-peer (P2P) — all computers equal, share resources directly (small networks).
- Client–server — central servers provide services to clients (web, email, file servers).
Network topologies
| Topology | Structure | Advantages | Disadvantages |
|---|---|---|---|
| Bus | All devices on a single backbone cable with terminators | Simple, less cable | Backbone failure stops network; collisions; hard to troubleshoot |
| Star | All devices connected to a central hub/switch | Easy to install and manage; one cable failure affects one device | Central device failure stops network; more cable |
| Ring | Devices in a closed loop; data passes in one direction (token) | Orderly access | One break can disrupt (unless dual ring) |
| Mesh | Every device connected to every other (full mesh) | Highly reliable, redundant | Expensive, complex; links |
| Tree (hierarchical) | Star networks connected in a hierarchy | Scalable | Dependent on root/backbone |
| Hybrid | Combination | Flexible | Complex |
Network devices
| Device | Function | OSI layer (typical) |
|---|---|---|
| NIC (Network Interface Card) | Connects a device to a network; has a MAC address | Data link/physical |
| Repeater | Regenerates/amplifies signals to extend distance | Physical |
| Hub | Connects devices; broadcasts data to all ports (not intelligent) | Physical |
| Switch | Connects devices; forwards data only to the destination port using MAC addresses | Data link |
| Bridge | Connects two LAN segments, filters traffic | Data link |
| Router | Connects different networks and routes packets using IP addresses (e.g. home network to internet) | Network |
| Gateway | Connects networks using different protocols (protocol conversion) | Upper layers |
| Modem (modulator–demodulator) | Converts digital signals to analog and back for transmission over telephone/cable lines | Physical |
| Wireless access point | Provides Wi-Fi connectivity to a wired network | Data link |
| Firewall | Filters traffic based on security rules | Network and above |
Network models
OSI reference model (7 layers)
| Layer | Name | Function | Examples |
|---|---|---|---|
| 7 | Application | User services | HTTP, FTP, SMTP, DNS |
| 6 | Presentation | Data format, encryption, compression | SSL/TLS (partly), JPEG, ASCII |
| 5 | Session | Establish, manage, terminate sessions | NetBIOS, RPC |
| 4 | Transport | End-to-end delivery, reliability, flow control, segmentation | TCP (reliable, connection-oriented), UDP (fast, connectionless) |
| 3 | Network | Logical addressing and routing | IP, routers |
| 2 | Data link | Framing, MAC addressing, error detection | Ethernet, switches |
| 1 | Physical | Transmission of raw bits over media | Cables, hubs, repeaters |
Mnemonic (layer 1 to 7): "Please Do Not Throw Sausage Pizza Away".
TCP/IP model
Four layers: Application (OSI 5–7), Transport, Internet, Network access (link) — the practical model of the Internet.