WIRED TRANSMISSION


Introduction:

Wired Transmission is the cables that are tangible or have physical existence.

Wired Transmission is limited by the physical geography.

This type of Transmission is also called Guided Communication.

Each Transmission Media has its own characteristics like transmission speed, effect of noise, physical appearance, cost etc.

 

Types of Wired Transmission Media:

  • Twisted Pair Cable
  • Co-Axial Cable
  • Fibber Optical Cable

Twisted Pair Cable:

§  This cable is the most commonly used and is cheaper than others.

§  It is light weight, cheap, can be installed easily, and they support many different types of network.

§  A twisted pair consists of two insulated copper cables, twisted together to reduce electrical interference between adjacent pairs of wires.

§  Its frequency range is 0 to 3.5 kHz.

§  Typical attenuation is 0.2 dB/Km @ 1 kHz.

§  Typical delay is 50µs/km.

§  Repeater spacing is 2km.

§  This type of cable is still used in the subscriber loop of the public telephone system (the connection between a customer and the local telephone exchange), which can extend for several kilometres without amplification.

§  The subscriber loop is essentially an analogue transmission line.

§  Although twisted pair cables are also be used in computer networks to carry digital signals over short distances.

Types of Twisted Pair Cable:

  • Unshielded Twisted Pair

 

  • Shielded Twisted Pair

Unshielded Twisted Pair (UTP):

§  Twisted Pair is a pair of copper wires, with diameters of 0.4-0.8 mm, twisted together and wrapped with a plastic coating.

§  The twisting increases the electrical noise immunity, and reduces the bit error rate (BER) of the data transmission.

§  UTP cable consists of two conductors usually copper, each with its own colour plastic insulator.

§  Identification is the reason behind coloured plastic insulation.

§  UTP cables consist of 2 or 4 pairs of twisted cable.

§  Cable with 2 pair use RJ-11 connector and 4 pair cable use RJ-45 connector.

Advantages:

§  Easy to Install.

§  It is flexible.

§  It is cheaper than other cables.

§  It has high speed capacity.

§  Limited range is 100 meters.

§  Higher grades of UTP are used in LAN technologies like Ethernet.

Disadvantages:

§  Bandwidth is low when compared with Coaxial Cable.

§  Provides less protection from interference.

Shielded Twisted Pair (STP):

§  Shielded Twisted Pair (STP) cable was introduced in the 1980s by IBM as the recommended cable for their Token Ring network technology.

§  It is similar to unshielded twisted pair cable except that each pair is individually foil shielded, and the cable has a braided drain wire.

§  Electromagnetic noise penetration is prevented by metal casing. Shielding also eliminates crosstalk.

§  It has same attenuation as unshielded twisted pair.

§  It is faster the unshielded and coaxial cable.

§  It is more expensive than coaxial and unshielded twisted pair.

Advantages:

§  Easy to install.

§  Performance is adequate.

§  STP can be used for Analog or Digital transmission.

§  STP increases the signalling rate.

§  STP has higher capacity than UTP.

§  STP eliminates crosstalk which is the main issue in UTP wires.

Disadvantages:

§  STP is heavier than other cables.

§  STP is also more difficult to manufacture.


Co-Axial Cable:

§  Coaxial cable is very common and widely used in Communication media. For example TV wire is usually Coaxial.

§  Coaxial cable has two wires of copper. The core wire lies in the center and it is made of solid conductor.

§  The core is enclosed in an insulating sheath.

§  The second wire is wrapped around over the sheath and that too in turn encased by insulator sheath.

§  This all is covered by plastic cover.

§  Because of its structure, the coaxial cable is capable of carrying high frequency signals than that of twisted pair cable.

§  The wrapped structure provides it a good shield against noise and cross talk.

§  Coaxial cables provide high bandwidth rates of up to 450 mbps.

§  The most common Coaxial Standards are: 50-Ohm RG-7 or RG-11: used with thick Ethernet,50-Ohm RG-58: used with thin Ethernet,75-Ohm RG-59:used with cable television, 93-Ohm RG-62: used with ARCNET.

Types of Co-Axial Cable:

  • Baseband Transmission

 

  • Broadband Transmission

Baseband Transmission:

§  Digital signals are used in baseband transmission.

§  Frequency division multiplexing is not possible in baseband transmission.

§  Baseband is bi-directional transmission.

§  It covers short distance.

§  Entire bandwidth of the cable is consumed by a single signal in a baseband transmission.

Broadband Transmission:

§  Analog signals are used in broadband transmission.

§  Transmission of data is unidirectional in broadband transmission.

§  It covers long distance.

§  Frequency division multiplexing is possible in broadband transmission.

§  The signals are sent on multiple frequencies and allow all the multiple signals are sent simultaneously in broadband transmission.

Advantages:

§  Bandwidth is high.

§  Used in long distance telephone lines.

§  Transmits digital signals at a very high rate of 10Mbps.

§  Much higher noise immunity.

§  Data is transmitted without distortion.

Disadvantages:

§  If single cable fails then entire network can fail.

§  Coaxial cable is difficult to install and more expensive than twisted pair.

Fibber Optical Cable:

§  Fibber optic cable uses electrical signals to transmit data. It works on the properties of light.

§  At the centre is the glass core through which light propagates.

§  Optical fibres are thin, solid strands of glass that transmit information as pulses of light.

§  The fibber has a core of high-purity glass, between 6μm and 50μm in diameter, down which the light pulses travel.

§  The core is surrounded by glass cladding with lower index of refraction.

§  This is covered with a thin plastic jacket to protect the cladding.

§  The fibbers are grouped together in bundles protected by an outer shield.

§  The fibber has more than 2 gbps (Gigabytes per Second) bandwidth.

Characteristics:

§  The fibber cable is expensive.

§  Very hard to install.

§  The fibber cable is capable of extremely high speed.

§  The fibber cable has extremely low attenuation.

Advantages:

§  The fibber cable is fast than others.

§  It has Low attenuation

§  No EMI interference is allowed in this wire.

Disadvantages:

§  It is very costly.

§  It is very hard to install.

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