Transmission Media and Classifications (Twisted Pair Cable, Coaxial Cable, Fiber optic Cable )

In a data transmission system, the transmission medium is the physical path between transmitter and receiver.

Classes of Transmission Media

Transmission Media 
  → Guided (Wired) 

• Twisted Pair Cable
• Coaxial Cable
• Fiber optic Cable

  → (Unguided wireless)

• Free Space

Related Design Factors

Following are the number of design factors relating to transmission media -

• Bandwidth : All other factors remaining constant , the greater the bandwidth of a signal, the higher the data rate can be achieved.
• Transmission impairments : Impairments, such as attenuation, limit the distance.
• Interference : Interference from competing signals in overlapping frequency bands can distort or wipe out a signal.
• Number of receivers : A guided medium can be used to construct a point-to-point link or a shared link with multiple attachments.

Twisted Pair 

The least expensive and most widely used guided transmission medium is twisted pair.

Physical Description :

A twisted pair consist of two insulated copper wires arranged in a regular spiral pattern . A wire pair acts as a single communication link.

Application :

By far the most common guided transmission medium for both analog and digital signals is twisted pair. It is the most commonly used medium in the telephone network and is the workhorse for communications within buildings.

Twisted Pair can be divided into following categories -

• Unshielded Twisted Pair and
• Shielded Twisted Pair

EIA - 568 - A recognizes three categories of UTP cabling :

• Category 3: UTP cables and associated connecting hardware whose transmission characteristics are specified up to 16 MHz
• Category 4: UTP cables and associated connecting hardware whose transmission characteristics are specified upto 20 MHz
• Category 5: UTP cables and associated connecting hardware whose transmission characteristics are specified upto 100 MHz.

Coaxial Cable

Coaxial cable has a central core conductor of solid or stranded wire (usually copper) enclosed in an insulating sheath, which is in turn, encased in an outer conductor of metal foil, braid, or a combination of the two. This outer conductor is also enclosed in an insulating sheath, and the whole cable is protected by a plastic cover.

Applications

Coaxial cable is a versatile transmission medium, used in a wide variety of applications. The most important of these are 

• Television distribution
• Long-distance telephone transmission
• Short-run computer system links
• Local area network

Optical Fiber 

An optical fiber is a thin (2 to 125 μm), flexible medium capable of guiding an optical ray. Various glasses and plastics can be used to make optical fibers.

The core is the innermost section and consists of one or more very thin strands or fibers, made of glass or plastic; the core has a diameter in the range of 8 to 50 μm. Each fiber is surrounded by its own cladding and family the whole entity in a jacket for protection.

Propagation Modes