Guided Transmission Media

The Presentation describes about the Transmission media and in detail about coaxial cable,Twisted pair, Fiber optics, Power lines and their comparisons

1. Transmission media By S.Rajapriya,MS (IT)., Assistant Professor of IT V.V.Vanniaperumal College for Women

2. TRANSMISSION MEDIA A transmission medium is a physical path between the transmitter and the receiver ( i.e ) it is the channel through which data is sent from one place to another . Transmission Media is broadly classified into the following types: 

3. Guided transmission media It is also referred to as Bounded transmission media. Signals being transmitted are directed and confined in a narrow pathway by using physical links.  Features:    High Speed Secure Used for comparatively shorter distances There are 3 major types of Guided Media: 

4. 2.1 Magnetic media One of the most convenient way to transfer data from one computer to another, even before the birth of networking, was to save it on some storage media and transfer physical from one station to another . For example, a bank has to handle and transfer huge data of its customer, which stores a backup of it at some geographically far-away place for security reasons and to keep it from uncertain calamities . If the bank needs to store its huge backup data then its transfer through internet is not feasible . The WAN links may not support such high speed.Even if they do; the cost is too high to afford. In these cases, data backup is stored onto magnetic tapes or magnetic discs, and then shifted physically at remote places.

5. 2.2 Twisted pair Although the bandwidth characteristics of magnetic tape are excellent, the delay characteristics are poor. A twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together, as shown in fig. below One of the wires is used to carry signals to the receiver, and the other is used only as a ground reference. The receiver uses the difference between the two. In addition to the signal sent by the sender on one of the wires, noise and crosstalk may affect both wires and create unwanted signals.

6. Twisted pair By twisting the pairs, a balance is maintained. The number of twists per unit of length(e.g., inch) has some effect on the quality of the cable . Twisted Pair is of two types: 

7. Unshielded twisted pair ( utp ) This type of cable has the ability to block interference and does not depend on a physical shield for this purpose . It is used for telephonic applications.  Advantages:  Least expensive Easy to install High speed capacity Susceptible to external interference Lower capacity and performance in comparison to STP UTP has seven categories, each suitable for specific use. In computer networks, Cat-5, Cat-5e, and Cat-6 cables are mostly used.

8. Shielded twisted pair ( stp ) This type of cable consists of a special jacket to block external interference . It is used in fast-data-rate Ethernet and in voice and data channels of telephone lines.  Advantages:  Better performance at a higher data rate Eliminates crosstalk Comparitively faster Comparitively difficult to install More expensive Bulky

9. 2.3 Coaxial cable Coaxial cable (or coax) carries signals of higher frequency ranges than those in twisted pair cable. It has an outer plastic covering containing 2 parallel conductors each having a separate insulated protection cover. Coaxial cable transmits information in two modes: Baseband mode Broadband mode Cable TVs and analog television networks widely use Coaxial cables. 

10. Coaxial cable Advantages:    High Bandwidth Better noise Immunity Easy to install and expand Inexpensive Disadvantages:    Single cable failure can disrupt the entire network

11. 2.4 power lines Power Line communication (PLC) is Layer-1 (Physical Layer) technology which uses power cables to transmit data signals . In PLC, modulated data is sent over the cables. The receiver on the other end de-modulates and interprets the data. Because power lines are widely deployed, PLC can make all powered devices controlled and monitored. PLC works in half-duplex. There are two types of PLC: Narrow band PLC Broad band PLC Narrow band PLC provides lower data rates up to 100s of kbps, as they work at lower frequencies (3-5000 kHz).They can be spread over several kilometers. Broadband PLC provides higher data rates up to 100s of Mbps and works at higher frequencies (1.8 – 250 MHz).They cannot be as much extended as Narrowband PLC.

12. 2.5 Fiber optic cable Structure of Optical Fiber : It has three parts • Core : It is a central tube as shown in the diagram. It is of skinny size and made up of the optically transparent dielectric medium. It carries the light from the transmitter to the receiver.The diameter of the core varies from 5um to 100um. • Cladding : it is the outer optical material surrounding the core. Its reflective index is lower than the core. It helps to keep the light within the core as it uses the phenomena of total internal reflection. • Buffer coating : It is the plastic coating which protects the fiber . It is made up of silicon rubber. The diameter of the fiber after the coating is 250-300um.

13. Transmission of light through fiber A fiber optic cable is a light pipe which is used to carry a light beam from one place to another. Light is an electromagnetic signal and can be modulated by information. Since the frequency of light is extremely high hence it can accommodate wide bandwidths of information, also higher data rate can be achieved with excellent reliability. The modulated light travel along the fiber and at the far end, are converted to an electrical signal by means of a photo electric cell. Thus the original input signal is recovered at the far end. FOC may be multimode or signal mode. Multimode fibers use multiple light paths whereas signal mode fibers allow a single light path and are typically used with laser signaling .

14. Fiber optic – advantages & disadvantages Advantages:    Increased capacity and bandwidth Light weight Less signal attenuation Immunity to electromagnetic interference Resistance to corrosive materials Disadvantages:    Difficult to install and maintain High cost Fragile

15. Comparison of fiber optics and copper wire S.No . Basis Fiber Optics Copper Wire 1. Data Carrier It carries data in the form of light. It carries data in the form of electric signals. 2. Bandwidth It offers higher bandwidth. It offers lower bandwidth. 3. Structure It is thin, lighter in weight and smaller in size. It is heavier and thicker. 4. Environment It can be laid in different environment because it is more resistant to corrosive materials. It cannot be laid in different environment because it is more prone to corrosive materials. 5. Attenuation Attenuation is very low. Attenuation is high.

16. S.No . Basis Fiber Optics Copper Wire 6. Interface As in this data travel in the form of light, they are not affected by electrical and magnetic interface. As in this data travel in the form of electric signals, they are affected by electrical and magnetic interface. 7. Security They provide security against the wiretappers , because there is no leakage of light and are difficult to tap. They does not provide security against the wiretappers , because there is leakage of signals and are easy to tap. 8. Cross-talk problem There is no such kind of any problem. These are prevalent this problem. 9. Effect on charge carriers In this charge carriers are photons, they do not carry any charge, so they does not get affected. In this charge carriers are electrons, they carry negative charge, so they get affected when they move in a wire. 10. Break-ability They are easily breakable. They cannot be easily broken. 11. Installation Cost Installation Cost is high. Installation Cost is less.

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