Ch 11 explores data communication — how data travels from sender to receiver through various transmission media, modes of communication, switching techniques, and the evolution of mobile communication.
Data communication components: sender, receiver, message, medium (channel), protocol. Transmission modes: Simplex (one direction — keyboard, TV broadcast), Half-duplex (both directions but not simultaneously — walkie-talkie), Full-duplex (both directions simultaneously — phone call, internet). Guided media: Twisted pair cable (cheap, short distance, susceptible to interference), Coaxial cable (better shielding, cable TV), Fibre optic (light pulses, fastest, longest distance, immune to electromagnetic interference, expensive). Unguided: Radio waves (long range, penetrate buildings), Microwaves (line-of-sight, satellite communication), Infrared (short range, TV remote).
Switching techniques: Circuit switching (dedicated path for entire call duration — traditional telephone), Packet switching (data split into packets, each may take different route, reassembled at destination — internet), Message switching (entire message stored-and-forwarded at each node). Bandwidth: data carrying capacity of a channel (bps, Kbps, Mbps, Gbps). Mobile evolution: 1G (analog voice), 2G (digital voice, SMS), 3G (mobile internet, video calls), 4G/LTE (high-speed data, HD streaming, 100Mbps+), 5G (ultra-fast 1-10 Gbps, low latency, IoT, autonomous vehicles). Wi-Fi standards: 802.11 a/b/g/n/ac/ax.
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Fibre optic advantages: (1) Speed: carries light (3×10⁸ m/s) — bandwidth of Tbps. (2) Distance: signals travel up to 100km without repeaters (copper: ~100m for Ethernet). (3) No electromagnetic interference — immune to EMI/RFI. (4) Security: very difficult to tap without detection. (5) Thin and lightweight — more capacity in less space. Disadvantages: higher cost, fragile (bending can break), requires specialised installation. For backbone networks, undersea cables, and long-distance communication, fibre optic is the clear choice.
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