When bits travel across a wire, a fibre or the open air, noise can flip a 0 into a 1. Error detection lets the receiver notice that damage. Transmission media are the physical paths the bits travel on. Line coding is how we turn 1s and 0s into an electrical or optical signal on those media. These three ideas are among the most heavily tested items in the Physical and Data-Link layer portion of BCS, Bank IT-officer and other government IT exams, and questions are usually calculative (compute a parity bit, a CRC remainder, a Nyquist rate) or compare-and-contrast (UTP vs STP, single-mode vs multimode, ASK vs FSK). This lesson builds every idea from first principles and drills the exact question types examiners use.
Learning objectives
- Compute an even/odd parity bit for an ASCII character and state parity's limits.
- Explain and compute a checksum using one's-complement addition.
- Perform CRC using binary polynomial long division (XOR), and produce the transmitted codeword.
- State the idea behind Hamming code and how many bits it can detect/correct.
- Classify guided media (twisted pair STP/UTP, Cat5/Cat6, coaxial, optical fibre) and unguided media (radio, microwave, infrared) with their properties.
- Explain optical fibre: core, cladding, total internal reflection, single-mode vs multimode.
- Distinguish straight-through vs crossover cables and the T568A / T568B colour codes.
- Describe analog modulation (AM, FM, PM) and digital modulation (ASK, FSK, PSK, QPSK, QAM).
- Apply the sampling theorem, describe PCM and delta modulation.
- Draw and read line-coding waveforms: NRZ-L, NRZI, Manchester, RZ, AMI.