Data Communication and Computer Networks
What the exam tests
Data Communication and Computer Networks tests transmission media, topologies, network types, the OSI/TCP-IP models, devices, addressing and protocols. Questions ask you to choose a device, identify a topology or calculate addresses.
Core rules
- A network links devices to share data and resources. LAN is local, MAN covers a city, WAN spans countries.
- Topologies: bus, star, ring, mesh, tree and hybrid. Star is easy to troubleshoot but depends on the central switch; mesh gives redundant paths at higher cost.
- OSI layers: Physical, Data Link, Network, Transport, Session, Presentation, Application. TCP/IP maps to Network Access, Internet, Transport and Application.
- Devices: hub repeats to all ports; switch forwards by MAC address; router forwards between networks by IP address; modem modulates/demodulates.
- Media: twisted pair, coaxial, fibre optic (immune to EMI, high bandwidth) and wireless.
- IPv4 is 32-bit; private ranges include 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. MAC addresses are 48-bit hardware addresses.
Worked example
Host 192.168.1.10/24. The /24 prefix means 24 network bits and 8 host bits. Network address: 192.168.1.0. Broadcast address: 192.168.1.255. Usable host range: 192.168.1.1 to 192.168.1.254, giving 2^8 − 2 = 254 hosts. The default gateway must be in the same subnet, for example 192.168.1.1.
Traps
A hub does not learn MAC addresses; a switch does. A router separates broadcast domains. 192.168.1.255 is not usable with /24. Do not confuse MAC (hardware) with IP (logical). Fibre does not use electrical signals. TCP is connection-oriented; UDP is connectionless.