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THE NETWORK TRANSMISSION MEDIUM: ALL STUDENTS MUST KNOW OF....


TWISTED PAIR CABLES

This type of cabling is used for telephone communications and most modern Ethernet networks.  A pair of wires forms a circuit that can transmit data.  A pair of wires forms a circuit that can transmit data.

If the pair of wires are not twisted, electromagnetic noises (ex:motor), will effect the closer wire more, than the further one, therefore causing error.

Twisted pairs are cables that are designed with two independent insulated wires wrapped around each other and with the goal to help to combat electromagnetic interference.

A twisted pair cable comprises of two separate insulated copper wires, which are twisted together and run in parallel. The copper wires are typically 1mm in diameter. One of the wires is used to transmit data and the other is the ground reference.

Twisted-pair cabling is often used in data networks for short and medium-length connections because of its relatively lower costs compared to optical fiber and coaxial cable.

There are two types of twisted pair cables, unshielded twisted pair cable and shielded twisted pair cable.

UNSHIELDED TWISTED PAIR (UTP)

Unshielded twisted pair (UTP) cables are widely used in the computer and telecommunications industry as Ethernet cables and telephone wires. In an UTP cable, conductors which form a single circuit are twisted around each other in order to cancel out electromagnetic interference (EMI) from external sources.

Unshielded means no additional shielding like meshes or aluminum foil, which add bulk, are used.

Typically wrapped in a plastic wrapper. (for mechanical protection)


SHIELDED TWISTED PAIR (STP)

Shielded twisted pair is a special kind of copper telephone wiring used in some business installations. ... To reduce crosstalk or electromagnetic induction between pairs of wires, two insulated copper wires are twisted around each other. Each signal on twisted pair requires both wires.

Shielded twisted pair (STP) cable was originally designed by IBM for token ring networks that include two individual wires covered with a foil shielding, which prevents electromagnetic interference, thereby transporting data faster.

it contains an extra foil wrapping or copper braid jacket to help shield the cable signals from interference. STP cables are costlier when compared to UTP, but has the advantage of being capable of supporting higher transmission rates across longer distances.

The additional covering in STP cable stops electromagnetic interference from leaking out of or into the cable.

STP cables are often used in Ethernet networks, particularly fast-data-rate Ethernets. The effectiveness of the additional covering varies according to the substance used for the shielding, such as:

  • Frequency
  • Thickness
  • Type of electromagnetic noise field
  • Distance from the shield to the noise source
  • Shield discontinuity
  • Grounding practices










COAXIAL CABLES

sometimes known as coax cable, is an electrical cable which transmits radio frequency (RF) signals from one point to another.

Coaxial cable has a distinct thick, round shape because of its interior insulation layer. Its size makes it look very different to other types of cable, such as twisted pair or Ethernet cable. 

Coaxial cables are a popular choice because their shielded design allows the centre conductor to transmit data quickly while being protected from damage and interference.

Coaxial cables are mainly built up of these four different layers:

1.  A centre conductor which is usually a copper wire, which data and video travels through

2.  Surrounding the copper wire is a dielectric plastic insulator

3.  A braided mesh made from copper then helps to shield the cable from electromagnetic interference (EMI)

4.  The external layer is a plastic coating which protects the internal layers from damage


Coaxial cable works by carrying data in the centre conductor, while the surrounding layers of shielding stop any signal loss (also called attenuation loss) and help reduce EMI.

The first layer, called the dielectric, provides distance between the core conductor and the outer layers, as well as some insulation.


FIBER OPTIC CABLES

Fiber-optic cables transmit data via fast-traveling pulses of light. Another layer of glass, called “cladding,” is wrapped around the central fiber and causes light to repeatedly bounce off the walls of the cable rather than leak out at the edges, enabling the single to go farther without attenuation.

Common light sources: LEDs & Lasers


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