Guided Transmission Media: Twisted Pair, Coaxial Cable, and Optical Fiber

Guided Media (also called Wired Media or Bounded Media) refers to physical communication cables that guide electrical or optical signals along a specific physical path from sender to receiver.

The three primary guided media are Twisted Pair, Coaxial Cable, and Optical Fiber.

1. Twisted Pair Cable

Consists of two insulated copper wires twisted around each other in a helical spiral.

Why are the wires twisted? To cancel out electromagnetic interference (EMI) and crosstalk from adjacent wire pairs.
Two Major Varieties:
1. UTP (Unshielded Twisted Pair): Cheap, flexible, used in standard office Ethernet cables (Cat5e, Cat6) with RJ-45 plastic connectors.
2. STP (Shielded Twisted Pair): Has an extra metal foil shield around the wires to block heavy factory electrical noise.

2. Coaxial Cable

Consists of a central solid copper conductor core surrounded by a flexible insulating layer, an outer braided copper/aluminum mesh shield, and a tough plastic jacket.

Analogy: Your home cable TV wire (Dish TV / Hathway wire) connected to the back of your television set!
Connectors Used: BNC (Bayonet Neill-Concelman) connectors and F-type screw connectors.
Advantage: Better noise immunity and higher bandwidth than twisted pair.

3. Optical Fiber Cable (The Speed King)

Instead of moving electrical voltages through copper, Optical Fiber transmits data as pulses of light through hair-thin strands of ultra-pure glass (silica) or plastic.

Physical Principle: Total Internal Reflection (TIR)

Light rays enter the inner Core (refractive index n1).
When light hits the boundary of the outer glass Cladding (refractive index n2) at an angle greater than the critical angle, 100% of the light bounces back inside without escaping.

Optical Fiber Construction

Inner Core

Ultra-thin glass strand where light travels (n1)

Cladding

Surrounding glass with lower refractive index (n2 < n1)

Buffer & Jacket

Protective silicone coating and tough outer Kevlar jacket

Single-Mode vs. Multi-Mode Fiber:

Single-Mode Fiber (SMF): Extremely narrow core (8-10 microns); light travels in one straight line using laser light. Used for long-distance telecommunications across cities and underwater oceans (up to 100 km without repeaters).
Multi-Mode Fiber (MMF): Wider core (50-62.5 microns); light bounces at multiple angles using cheap LED sources. Used for short-distance connections inside data centers (up to 500 meters).

4. Master Comparison Table for Exams

Parameter	Twisted Pair (Cat6)	Coaxial Cable	Optical Fiber
Signal Type	Electrical voltage	Electrical voltage	Light pulses (Photons)
Material	Copper wire	Solid copper + mesh	Pure glass (Silica)
Data Rate (Speed)	100 Mbps to 10 Gbps	10 Mbps to 100 Mbps	100 Gbps to Terabits/sec
Distance (Range)	Max 100 meters per segment	200 to 500 meters	Tens of kilometers
EMI / Noise Immunity	Low (Susceptible to noise)	Moderate	100% Immune (No electricity)
Installation Cost	Cheapest & easiest	Moderate	Most expensive & fragile
Connectors	RJ-45	BNC, F-type	SC, LC, ST optical connectors

💡 DAVV Exam Tip

Question (10 Marks): “Explain guided transmission media with neat sketches. Compare Twisted Pair, Coaxial, and Optical Fiber cables.”

Draw the cross-section diagram of Optical Fiber (Core, Cladding, Jacket) and explain Total Internal Reflection.

Explain why twisting wires reduces crosstalk in Twisted Pair cables.

Write the 7-parameter comparison table above.

Guided Transmission Media: Twisted Pair, Coaxial & Fiber Optic