transmission Media

                 

                                                           *Transmission Media

     Transmission media is a pathway that carries the information from sender to receiver. We use different types of cables or waves to transmit data. Data is transmittednormally through electrical or electromagnetic signals. An electrical signal is in the form of current. An electromagnetic signal is series of electromagnetic energy pulses at various frequencies. These signals can be transmitted through copper wires, optical fibers.


 1. The transmission medium is the physical path by which a message travels from sender to receiver.

2.Computers and telecommunication devices use signals to represent data.
These signals are transmitted from a device to another in the  form of electromagnetic energy.

3.Examples  of Electromagnetic energy include power, radio waves, infrared light, visible light, ultraviolet light, and X and gamma rays.

4.All  these electromagnetic signals constitute  the  electromagnetic.

              1. Guided  media(or wired media),

  which are those that provide  a conduit from one device to another. It has physical existance.

                                                       Examples: twisted-pair, coaxial cable, optical fiber.

            2.Unguided media (or wireless media) 

 transport data without cables these are wireless.
           

                        Guided Media
(Wired Media)

There are three    types:-            
                                                         

Twisted-pair cable
Coaxial cable
Fiber-optic cable

 Twisted pair cable   

Twisted pair cable is the most widely used medium for telecommunicaton. Twisted pair wires are used in telephones wires which consist of two insulated copper wires twisted into pairs and used for voice.A twisted pair cable is made of two plastic insulated copper wires twisted together to form a single media. Out of these two wires, only one carries actual signal and another is used for ground reference. The twists between wires are helpful in reducing noise (electro-magnetic interference) and crosstalk. and data transmission.

      Type of twisted pair cable

   STB-Stands for sheilded cable.

 The metal casing prevents the penetration of electromagnetic noise.
   

   Unshielded twisted cable

 
Any medium can transmit only a fixed range of frequencies!
UTP cable is the most common type of telecommunication medium in use today.

The range  is suitable for transmitting both data and video.
Advantages of UTP  are its cost and ease of use. UTP is cheap, flexible, and easy to install.

UTP connectors

The most common UTP connector is RJ45 (RJ stands  for  Registered Jack).

Applications of twisted pair cable

   Twisted-pair cables are used in telephones lines to provide voice and data channels.
The DSL lines that are used by the telephone companies to provide high data rate connections also use the high-bandwidth capability of unshielded twisted-pair cables.
Local area networks, such as 10Base-T and 100Base-T, also used UTP cables.

Coaxiale cable

Coaxial cable is widely used for cable television systems, office buildings and other worksites or workstations for local area network. The cables consists of copper or aluminium wire wrapped with insulating layer. Transmission speed range is from 200 million to more then 500 million bites per seconds. It is cable which is used in TV companies.A cable that is used in videos, communications and audio. This cable has high bandwidths and greater transmission capacity.
 

advantage

Higher bandwidth
400 to 600Mhz
up to 10,800 voice conversations
Much less susceptible to interference than twisted pair

disadvantsge

High attenuation rate makes it expensive over long distance
Attenuation means loss of energy. Some times the strength of the signal falls off with distance over any transmission medium then attenuations is occurred

Optical fibre cable

Optical fibre cable consists of one or more filaments of glass fibre wrapped in protective layers that are used to carry light. It uses light signals and have very high bandwidth. It transmits light which can travel over extended distances. The transmission speed of optical fibre cable is hundreds times faster then coaxiale cable nd thousands times faster the twisted pair cable.

Metal  cables transmit signals in the form of  electric current.
Optical fiber is made of glass or plastic and transmits signals in the form of light.
Light, a  form of electromagnetic energy,   travels at 300,000 Kilometers/second ( 186,000 miles/second), in a vacuum.
The speed of the light depends on the density of the medium through which  it is traveling ( the higher density, the slower the speed).

     the nature of light

Light travels in a straight line as long as it is moving through a single uniform substance.

If a ray of light traveling through one  substance suddenly enters another (less or more dense) substance, its speed  changes abruptly, causing the ray to change direction. This change is called refraction.

types of optical fiber

There are two basic types of fiber:

multimode fiber and single-mode fiber. 

Multimode fiber is best designed for short transmission distances, and is suited for use in LAN systems and video surveillance.

Single-mode fiber is best designed for longer transmission distances, making it suitable for long-distance telephony and multichannel television broadcast systems

 fiber optical cable  connector

The subscriber channel (SC) connector is used in cable TV. It uses a push/pull locking system. The straight-tip (ST) connector is used for connecting cable  to networking devices. MT-RJ is a new connector with the same size as  RJ45.eg STB SET TOP BOX

  advantage

The major advantages offered by fiber-optic cable over twisted-pair and coaxial cable are noise resistance, less signal attenuation, and higher bandwidth.

 Noise Resistance:

because fiber-optic transmission uses light rather than electricity, noise is not a factor. External light, the only possible interference, is blocked  from the channel by the outer jacket.

Less signal attenuation

Fiber-optic transmission  distance is significantly greater than that of other guided media. A signal can run for miles without requiring regeneration.
Higher bandwidth
Currently, data rates and bandwidth utilization over fiber-optic cable are limited not by the medium but by the signal generation and reception technology available.
             

           disadvantage

The main disadvantages of fiber optics are cost, installation/maintenance, and fragility.
Cost.  Fiber-optic cable is expensive. Also, a laser light source can cost thousands of dollars, compared to hundreds of dollars for electrical signal generators.
Installation/maintenance
Fragility. Glass fiber is more easily broken than wire, making it less useful for applications  where hardware portability is required.