Duties of the Physical Layer

• Converts data bits into signals (electrical, optical, or radio) suitable for the transmission medium, and vice versa on receipt.
• Defines mechanical and electrical specs of connectors and cables (pin layout, voltage levels).
• Specifies data rate (bits/sec) and bit duration.
• Handles synchronization between sender and receiver clocks.
• Defines line configuration (point-to-point vs multipoint) and transmission mode (simplex/half-duplex/full-duplex).
• Determines physical topology (bus, star, ring, mesh).

Fiber Optic vs Twisted Pair

Aspect	Fiber Optic Cable	Twisted Pair Cable
Signal type	Light pulses	Electrical signals
Bandwidth/Speed	Very high (Gbps–Tbps range)	Lower (up to ~10 Gbps for Cat6a)
Attenuation	Very low — supports long distances without repeaters	Higher — needs repeaters more often over distance
EMI immunity	Immune to electromagnetic interference	Susceptible to EMI and crosstalk
Cost	More expensive, harder to install/splice	Cheaper, easier to install
Security	Hard to tap without detection	Easier to tap/eavesdrop
Typical use	Backbone links, long-haul, high-speed networks	LANs, short-to-medium distance connections