Chapter 3

1. Chapter 3 Transmission Media Visit to more Learning Resources

3. Transmission media is a medium over which information travels from the sender to receiver. • Different media have different properties and used in different environments for different purpose. • The purpose of physical layer is to transport a raw bit stream from one computer to other.

4. Types of media 1. Guided media(wired media):- it is a communication medium which needs to have point to point physical connection. Copper wires & fiber optics can be used as a guided media. 2. Unguided Media (wireless media):- signal energy propogates in the form of eletromagnetic waves.In this communication medium is Air.

5. Criteria for the selection of transmission media • Types of medium (wired or wireless) • Number of conductor • Flexibility • Durability • Reliability of connection • Required Speed • Cost • Ease of installation & maintenance access • Technical expertise required to install & configure • Attenuation

6. Classification of transmission media

7. 1. Twisted pair cable • Types of twisted pair

8. Shielded twisted pair • STP has a metal foil or braided mesh to cover each pair of insulating conductors known as metal shield. • It reduces the interference of the noise but makes the cable bulky and expensive. • So practically UTP is more used than STP. • Twisted pair can be either used for analog or digital transmission. • The bandwidth supported by the wire depends on the thickness of the wire and the distance travelled.

9. Characteristics of STP • Twisted conductors are shielded to reduce noise. • Low cost medium • Used only for IBM computers • Supports data rates upto mbps.

10. UTP • Twisted pair consist of two insulated conductor twisted together in the spiral form as shown in fig. • UTP cables are very cheap and easy to install. But they are badly affceted by the noise interference.

11. Why to twist the wires? • Twisting of wires will reduce the effect of noise or external interference. • Number of twists per unit length will determine the quality of cable. More twist means better quality.

12. Characteristics of UTP • Shielding is not used. • Noise interference is high. • Low cost medium. • Can support data rate of several mbps • Installation is easy • Used in telephone, DSL(Digital Subscriber Line) modem, LAN, ISDN(Integrated Services Digital Network).

13. UTP Cables • CAT 3:- used in LAN, office buildings etc, proper design, limited distance, data rates upto 16 mbps, 16 MHz. • CAT 5:- 100 MHz, data rates of 100 mbps, limited distance.

14. Application of twisted pair • In telephone lines to carry voice and data signals • In LAN • In the DSL • ISDN

15. Comparison of twisted pair cables

16. 2. Coaxial cable

19. It consist of two concentric conductors separated by a dielectric material. • The external conductor is metallic and used for the purpose of shielding. • Shielding protects the wire from electromagnetic interference. • A plastic jacket which is cover of cable provides protection and insulation. • Coaxial cable used in telephone network, cable television system, Ethernet LAN because of large bandwidth and high noise immunity.

20. Characteristics • It is having 50 – 75 ohm impedance • Large bandwidth and low data loss • Excellent noise immunity • Costly than TP but cheaper than fiber optic • Data rate 10 mbps (you can increase data rate by increasing the diameter of inner conductor) • Maximum 30-100 nodes can connect.

21. Applications • Analog Telephone system • Digital phone system • Cable TV • Ethernet LAN • Digital transmission

22. Advantages • Excellent noise immunity due to shielding • Large bandwidth • Data losses are small • High data transfer rate • Less attenuation • Easy to install

23. Disadvantages • Expensive than TP cable • BNC connector are required for connection

24. 3.Optical fiber cables

25. It consist of an inner glass core surrounded by a glass cladding which has a lower refractive index. Digital signals are transmitted in the form of intensity, modulated light signal which is trapped in the glass core. Light is launched into fiber using a light source such as LED or laser. The optic fiber cables are costlier than other two types but they have many advantages over other two types.

26. Characteristics • High bandwidth (100 mbps to 2 gbps) • Light has much higher frequency than electricity. • Number of nodes support does not depend on its length. • Lower attenuation • Can carry signals to longer distance without amplifiers and repeaters. • Not affected by EMI • Cost is high compared to other 2 types. • Installation of fiber optic cable is difficult and tedious.

27. Advantages • Small size and lightweight • Easy availability and low cost • No electrical or electromagnetic interference • Large bandwidth • No crosstalk • Signal can be sent up to 100 times faster • Intermediate amplifiers not required • Fiber optic cable is flexible • Not affected by drastic environmental conditions.

28. Disadvantages • Initial cost is high • Joining the fiber optic is a difficult job.

29. Unguided(wireless) media Unguided media does not use a conductor or wire as a communication medium, it uses air or vacuum. The transmitter first converts data signal into electromagnetic waves and transmits them using a suitable antenna. The receiver receives them using a receiving antenna and converts the EM waves into data signal again.

30. . Fig: Electromagnetic spectrum for wireless communication

32. 1.Radio Wave transmission Radio Waves are easy to generate, can travel long distance and can penetrate buildings easily so they are widely used for communication both indoors and outdoors. They are broadcast omnidirectionally meaning that they travel in all directions from the source. Hence, transmitter and receiver do not have to be carefully aligned physically. This waves have Frequency between 10kHz & 1GHz

34. 2.Microwave transmission system --Microwaves are unidirectional electromagnetic waves with a frequency range from 1 to 300GHz. --Microwaves use space wave Propagation. Also it is line of sight communication. --Large Bandwidth, also it support high data rates.

36. Application of Microwave transmission --One to one communication --In celluar phones --In satellite n/w's --In the wireless LAN's

37. 3. Infrared transmission system --These waves having frequency 300GHz to 400THz. --IR waves uses line of sight propogation. --IR light is that it can't penetrate walls. That means it can be easily contained within room. --Large Bandwidth --It is used in very high speed in wireless LAN in future. --It will communicate point to point & Boradcast also

38. --For communication between keyboard, mouse, PC's & Printers.

39. Satellite Communication --An artificial satellite orbits or revolves around the earth. --A geostationary communication satellite is basically a relay station in space. --An earth station transmits information signal to the satellite using a highly directional dish antenna. --Satellite receives signal from one earth station amplifies it, improves the signal quality & radiates the signal back to other earth stations towards parabollic dish antenna. --The signal which being transmitted upwards to the satellite is called 'uplink' with normally frequency 6 GHz. --The signal which is transmitted back to the receiving earth station is called 'downlink' with frequency of 4GHz.

40. Parabolic Dish antenna Dish Antenna

41. Characteristics Satellite Communication -- Geostationary satellite can cover the entire earth. -- It supports bandwidth 1 to 10 Mbps. --Attenuation depends on frequency, power, antenna size & atmospheric condition. --The installation of satellite is extremely difficult & alignment of each station antenna must be perfectly aligned. --The cost of building & launching is very very expensive.

42. Latest Technologies in Wireless Networks: Bluetooth --Bluetooth is a wireless LAN technology which can connect devices such as telephones, computers, printers, cameras etc. Without using wires. --It connect one device to another with radio link. --Based on IEEE 802.15 standard. --short range(10 meters) --Limited speed --Low power --Low cost --Low complexity Bluetooth Architecture defines 2 types of n/w's 1. Piconets 2.Scatternet

43. 1.Piconets.. --It can have 8 stations. One of them called master & other called slaves. --The communication between master & slaves can be one to one or one to many.

44. 2.Scatternet.. --Fig shows 2 piconet. A slave in the first piconet can act as master in the second piconet. --It will receive message from master in 1st piconet acting slave & deliver message to the slaves in the 2nd piconet acting as a master.

45. Wi-Fi --Wi-fi is a popular technology which allows an electronic devices to exchange data or to connect to the internet using radio waves. --Wi-Fi stands for wireless fidelity. --Personal Computer,Smart phone, some digital cameras, Tablet use wifi --Based on IEEE 802.11 standards. --Wireless LAN are used in office building, colleges, Public areas.

47. Wi-Fi.. Advantages 1) Easy to use. 2) Easy and simple to expandability. 3) Easy to install and setup. 4) No requirement of wires Disadvantage 1) The range of Wi-Fi is limited 2) Security is less in Wi-Fi connections as compared with others.

48. Wi-Max --Long Form is Worldwide Interoperability for Microwave Access. --It is wireless communication standard provide data rates upto 1Gbps. --Less cost Uses/Application- --Provide portable mobile broadband connectivity. --Provide services voice on IP(VoIP) --Provide source of Internet connectivity --It is alternative to cable, digital subscriber line(DSL) for providing a broadband access.

49. Cellular(Mobile) Telephone System --Wireless communication --cell phone is not restricted to a one location can travel city, outside city --city is divided into small areas called ‘cell(around 10 sq km)’ --Each cell linked to MTSO, MTSO coordinates all mobile calls between an area of cell sites & central office. --Time & billing information for each mobile unit is accounted by MTSO --Cell site base station is provided transmit, receive & switch calls to & from any mobile unit within the cell to the MTSO.