Data Communication and Computer Networks
Data Communication and Computer Networks
This domain tests transmission fundamentals, media, topologies, network devices, addressing, and reference models. Expect questions that compare devices or modes, and simple calculations involving bits, bytes and time.
Core rules
- Data travels as analog or digital signals. Bandwidth is capacity; throughput is actual achieved rate. Latency is delay.
- Transmission modes: simplex one-way, half-duplex two-way but not simultaneously, full-duplex two-way simultaneously.
- Guided media include twisted pair, coaxial cable and optical fibre; unguided media include radio, microwave and infrared.
- Hub repeats to all ports; switch forwards by MAC address; router forwards between networks by IP address.
- Common topologies: bus, star, ring, mesh. Star is easy to isolate faults but depends on the central device.
Worked example
A 2 Mbps link carries how many bytes per second? 2 Mbps = 2,000,000 bits per second. Divide by 8: 250,000 bytes per second, or 250 KB/s in decimal units. In binary units this is about 244 KiB/s. The reasoning is unit conversion: Mbps is megabits, not megabytes, and one byte is eight bits.
Traps
Do not write MB/s when the link is Mbps. A hub is not a switch: a hub broadcasts, a switch learns MAC addresses. A router works with IP addresses, not just cables. Optical fibre is immune to electromagnetic interference but not infinitely fast. In full-duplex, capacity can be quoted per direction, so read the wording.