Communication Systems and Networking
Core concepts
Candidates should understand signal representation in time and frequency domains, Fourier concepts, bandwidth, and the Shannon capacity relationship. Know modulation schemes: AM, FM, ASK, FSK, PSK and QAM, and the trade-off between bandwidth efficiency and noise immunity. Study transmission media-twisted pair, coaxial, fibre-and impairments such as attenuation, noise, crosstalk and dispersion. Networking topics include the OSI and TCP/IP models, IP addressing and subnetting, Ethernet, switching versus routing, and common protocols (TCP, UDP, HTTP, MQTT). Understand error detection and correction, parity, checksums and CRC, plus serial standards such as RS-485 and CAN.
Traps
Questions often confuse the layers of the OSI model-know which layer handles addressing (network) versus framing (data link). Subnetting errors are common; always compute the mask and host range carefully. Another trap is mixing up bit rate and baud rate when multiple bits per symbol are used. Watch the difference between TCP (reliable, connection-oriented) and UDP (best-effort). In RF questions, decibel conversions and free-space path loss are frequently tested.
Worked example
A 192.168.1.0/26 network has 64 addresses; usable hosts are 62 after removing network and broadcast. Rule of thumb: usable hosts = 2^(32 − prefix) − 2. Always identify network and broadcast addresses before assigning hosts.