Data Communication Media Type - Computer Science - Networking

Data Communication

Media Type

Guided Transmission Media

•  Twisted Pair 

•  Coaxial cable 

•  Optical fiber

Twisted Pair (TP)

• Separately insulated
• Twisted together
• Often bundled into cables 
• Often referred to as UTP 
• Most common medium


Twisted Pair – Applications 
• Telephone network Between house and local exchange (subscriber loop) 
• Within buildings To private branch exchange (PBX)
• For local area networks (LAN) 10Mbps to 10Gbps



Twisted Pair -Pros & Cons
•  Cheap 
• Easy to work with
•  Low data rate compared to
• Short range


Twisted Pair – Characteristics
•  Analog -Amplifiers are used for long distances
•  Digital -Use either analog or digital signals, repeaters are used for long distances
•  Limited distance
•  Limited bandwidth
• Limited data rate
•  Susceptible to interference and noise


Unshielded and Shielded TP

•  Unshielded Twisted Pair (UTP)

– Ordinary telephone wire
– Cheapest 
– Easiest to install 
– Suffers from external EM interference
ex:- cat3, cat4, cat5/5e, cat6

•  Shielded Twisted Pair (STP)

– Metal braid or sheathing that reduces interference 
– Expensive than UTP 
– Harder to handle (thick, heavy)

Coaxial Cable

•  50 ohm – digital trans.
•  75 ohm – analog trans
•  Television distribution
•  Long distance telephone transmission
•  Slow Local area networks



Optical Fiber

•  Optical transmission

1. Light Source
2. Transmission Medium
3. Detector

Benefits of optical fiber
•  Greater capacity : data rates of hundreds of Gbps.
•  Smaller size & weight
•  Lower attenuation
•  Electromagnetic isolation
•  Greater repeater spacing

Characteristics
•   Act as wave guide for 1014 to 1015 Hz
       – Portions of infrared and visible spectrum .

•  Single-mode – light only propagates in straight lines without bouncing, expensive, but can be used for long distance, core 8-10 microns .

•   Multi-mode – many different rays will be bouncing around at different angles, core 50-65 microns (Cladding ~125 microns).

•  Silica based glass or plastic filaments are spun and packed into bundles of several hundreds or thousands.  Bundles may be put together as rods or ribbons and sheets.

•   These bundles are flexible and can be twisted and contorted to conduct light .

•  The thin glass center of the fiber where the light travels is called the “core core core core”. 

•  The outer optical material surrounding the core that reflects the light back into the core is called the “cladding cladding cladding cladding”. 

• In order to protect the optical surface from moisture and damage, it is coated with a layer of buffer coating.

Wireless Transmission(Unguided media)

•  Transmission and reception via antenna.
•   Directional 
     – Focused beam 
     – Careful alignment required
•   Omni-directional 
     – Signal spreads in all directions 
     – Can be received by many antennae

Wireless Categorization

• Satelite
• Personal
• LAN
• Fixed
• Mobile