Lecture 3(a) :Transmission Media

Media:

  Sending of data from one device to another is called transmission of data,Medium used to transmit the data is called Media like (Cables,Waves,Laser).Transmission of data through Medium is called Transmission Media.

Types of Media:

    Guided (Wired)

   Twisted Pair ,Coaxial cable, Fiber Optics.

       Unguided (Wireless)

                Radio waves,Microwaves,Infared waves.

 Lets Start From Guided Media:

Cable are divided into three types according to their speed, cost, need etc.
1. Twisted pair cable
2. Co-axial cable
3. Fiber optic cable

1. TWISTED PAIR CABLE:
A twisted pair wire consist of two bunches of thin copper wire and enclosed separately in a plastic insulator with conductor. One the wire is used to carry the signal to the receiver and the other is used as ground reference. The connectors used for this cables are called RJ45 (registered jack).
It is more flexible and easy to bend, cheaper than other cable and easy to install. They are of two types.

Unshielded twisted pair (UTP)
Shielded twisted pair (STP)

Unshielded twisted pair (UTP):
It content 8 separate copper conductor and they are arranged in 4 pair. The 4 pairs are then encased in a single sheath.

Category of UTP Cable:
CAT-1 traditional telephone line carries voice but not data
CAT-2 for data transmission up to 4Mbps
CAT-3 for data transmission up to 10Mbps
CAT-4 for data transmission up to 16Mbps
CAT -5 for data transmission up to 100Mbps
CAT-5(e) for data transmission up to 100to1000Mbps
CAT-6 for data transmission up to 1Gbps

 
Advantages:
1. In expensive media.
2. Easy to install.
3. Easy to bend.
4. Support up to 1Gbps.

Disadvantages:
1. Not suitable for long distance.
2. Signal can travel only 100 meter.
3. Easy gets affected by EMI (electro-magnetic interference).

UTP Cable description:

 
Max. Cable length……………..100 meter.
Band width…………………….100 Mbps.
Connector …………………….RJ 45
Bend radius …………………   360. / fit.
Resistance……………………..100 Ohms.
Signal transmission mode……….Base band. 

Shielded twisted pair (STP)

It is similar in construction UTP but it has additional foil (layer) or mesh shielding around each pair. The additional shielding in STP cable makes it preferable to UTP in installation where EMI is problem. STP is most expensive than UTP, resistance of this cable is 150 ohm. 

 

2-COAXIAL CABLE:

Coaxial cable consist the followings layers in its construction

–    The copper conductor

–    Insulation layer of plastic foam 

–    Second conductor or shield of wire mesh tube or metallic foil

–    Outer jacket of tough plastic

           Coaxial cable can be used over longer distances and support more stations on a shared line than

             twisted pair.

Types of Coaxial cable

1.       Thinnet 10base2 (10megabyte per second support 185 mtr.)

2.       Thicknet 10base5 (10megabyte per second support 500 mtr)

   Coaxial cable uses BNC connector.(British Novel Connector)

Advantages:

 Shielded allows signal to travel 500 meter.
 Unrepeated.
 Relative inexpensive.
 Medium difficult to install.

Disadvantages:
 Limited to 10 Mbps.
 Relative unreliable.
 Only usable in BUS topology
 Not the easy to install.
 Not the least expensive medium.

3. Fiber optic cable
A fiber optic cable is made of glass or plastic and transmits signals in the
form light because light travels much faster than electricity, physically. A fiber
optic cable consists of three concentric layers, the inner core, a cladding around it
and the outer protective coating. It provides a reliable, secure and very high band
width transmission media.

Type of fiber optic cable:
1. Single mode fiber optic cable:  it has core diameter of 8.3 micron and
the thickness of the core and cladding together is 125 micron. It referred as 8.3/125
single mode fiber optic. It uses a single wave length laser as a light source and
carry signal for extremely long distance.

2. Multi mode fiber optic cable:  it is rated as 62.5/125 Multi mode. It
uses a LED as a light source and carries multiple wave length. Both uses subscriber
connector and straight tip connectors.

Cable Problems:
Attenuation: Attenuation is signal deterioration, and noise which is signal interference can cause problems in networks because the data send may be interpreted incorrectly or not recognized at all after it has been received.
Noise:  Noise is any electric energy on the transmission cable that makes it difficult for a receiver to interpret the data sent from the transmitter.
Cross talk:  Cross talk involves the transmission of signal from wire to a nearby wire, when voltage change on a wire electromagnetic energy is generated. This energy radiates outward from the wire like a radio signal from a transmitter adjacent wire in the cable as like antennas and receives the transmitted energy which interferes with data on that wire.

In Next Post we will Discuss Unguided Media.