Computer Networks and Communication
What the exam tests
Network types and topologies, transmission media, devices, addressing, and the role of basic protocols.
Core concepts
- By size: PAN (Bluetooth), LAN (a computer lab), MAN (a city), WAN (countries, the Internet).
- Topologies: bus (one backbone, cheap, a single break downs the network), star (central switch, easy fault isolation, but the central device is a single point of failure), ring (one direction, token passing), mesh (redundant but costly).
- Media: twisted pair (RJ-45, about 100 m), coaxial, fibre optic (long distance, immune to electromagnetic interference), plus wireless.
- Devices: hub repeats to all ports, switch forwards by MAC address, router forwards between networks by IP, modem converts signals, gateway joins dissimilar networks.
- Addressing: MAC is 48-bit hardware; IPv4 is 32-bit. Class A is 1–126, B is 128–191, C is 192–223; 10.x, 172.16–31.x and 192.168.x are private.
- Protocols: TCP (reliable, connection-oriented), UDP (fast, no guarantee), IP, DNS, DHCP, HTTP, FTP, SMTP.
Worked example
Take the address 192.168.10.5. The first octet, 192, falls in 192–223, so it is Class C, with default mask 255.255.255.0 - 24 network bits and 8 host bits. Because it begins 192.168, it is a private address and is not routed on the Internet; a router must apply NAT before it can reach outside. The final .5 is the host part.
Traps
- A hub and a switch are not interchangeable: a switch learns MAC addresses, a hub does not.
- Bandwidth is capacity; throughput is what you actually achieve.
- IPv6 uses 128-bit addresses to solve address exhaustion, not because IPv4 was insecure.
- Simplex is one-way only; half-duplex is both ways but not at once.