1. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 1 5.0 Transmission Media broadly defined as anything that can carry information from a source to a destination. classes of transmission media :

2. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 2 5.1 Guided Media those that provide a conduit from one device to another – twisted-pair cable, coaxial cable and fiber-optic cable. signal traveling along the media is directed and contained by the physical limits of the medium. twisted-pair & coaxial cable – use metallic (copper) conductors that accept and transports signal in the form of electric current. optical fiber – cable that accepts and transports signal in the form of light.

3. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 3 5.1.1 Twisted-Pair Cable consists of two conductors (normally copper), each with its own plastic insulation and twisted together. one of the wire is used to carry signal to the receiver, and the other is used only a a ground reference. the receiver uses the difference (voltage/current) between the two. twisting makes both wires are equally affected by external influences (noise or crosstalk) number of twists per unit of length (e.g. inch) has some effect on the quality of the cable.

4. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 4 5.1.1 Twisted-Pair Cable Electromagnetic interference can create noise The noise over parallel wires results in an uneven load and a damaged signal

5. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 5 5.1.1 Twisted-Pair Cable Cumulative effect of noise is equal on both sides Twisting does not always eliminate the noise, but does significantly reduce it

6. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 6 5.1.1 Twisted-Pair Cable Unshielded vs. Shielded Twisted-Pair cable  the most common twisted-pair cable used in communications is referred to as Unshielded Twisted-Pair (UTP)  the Shielded Twisted-Pair (STP) was introduced by IBM – has a metal foil or braided mesh covering that encases each pair of insulated conductors.  metal casing in STP improves the quality of cable by preventing the penetration of noise and crosstalk but bulkier and more expensive.

7. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 7 5.1.1 Twisted-Pair Cable Categories of UTP based on Electronic Industries Association (EIA)

8. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 8 5.1.1 Twisted-Pair Cable Connectors for UTP  most common RJ45 (RJ stands for registered jack).  RJ45 is a keyed connector – connector can be inserted in only one way.

9. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 9 5.1.1 Twisted-Pair Cable UTP Performance  performance is measured by comparing the attenuation versus frequency and distance.  twisted-pair cable can pass a wide range of frequencies but the attenuation (dB/km) sharply increase with frequencies above 100 kHz.  gauge is a measure of thickness of the wire.

10. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 10 5.1.1 Twisted-Pair Cable Applications of Twisted-Pair cable  telephone lines to provide voice and data channels.  DSL lines to provide high-data-rate connections use the high-bandwidth capability of unshielded twisted-pair cable.  LAN networks – 10Base-T & 100Base-T

11. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 11 5.1.2 Coaxial Cable carries signals of higher frequency ranges than those in twisted-pair cable. has a central core conductor of solid or stranded wire (usually copper) enclosed in an insulating sheath the outer metallic wrapping serves both as a shield against noise and as the second conductor, which completes the circuit the outer conductor is also enclosed in an insulating sheath, and the whole cable is protected by a plastic cover

12. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 12 5.1.2 Coaxial Cable Coaxial Cable Standards  categorized by their radio government (RG) ratings  each RG number denotes a unique set of physical specifications, including the wire gauge of inner conductor, thickness and type of the inner insulator, construction of the shield, and the size and type of the outer casing.

13. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 13 5.1.2 Coaxial Cable Coaxial Cable connectors  the most common type – Bayone-Neill-Concelman (BNC)  BNC connector – used to connect the end of the cable to a device (e.g. TV set)  BNC T connector – used in Ethernet networks to branch out to a connection to other device  BNC terminator – used at the end of the cable to prevent the reflection of the signal.

14. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 14 5.1.2 Coaxial Cable Coaxial Cable Performance  attenuation is much higher in coaxial cable than in twisted- pair cable.  although has a much higher bandwidth, the signal weakens rapidly and requires the frequent use of repeaters

15. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 15 5.1.2 Coaxial Cable Coaxial Cable Applications  widely used in analog telephone networks where a single coaxial network could carry 10,000 voice signals.  then started to be used in digital telephone networks where a single coaxial cable could carry digital data up to 600 Mbps.  Cable TV networks  Ethernet LANs

16. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 16 5.1.3 Fiber-Optic Cable made of glass or plastic and transmits signals in the form light. use reflection to guide light through a channel – a glass or plastic core is surrounded by a cladding of less dense glass or plastic.

17. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 17 5.1.3 Fiber-Optic Cable Fiber Sizes  optical fibers are defined by the ratio of the diameter of their core to the diameter of their cladding, expressed in micrometers.

18. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 18 5.1.3 Fiber-Optic Cable Fiber Composition  outer jacket is made of either PVC or Teflon.  inside the jacket are Kevlar strands to strengthen the cable.  below the Kevlar is another plastic coating to cushion the fiber.  the fiber is at the center of the cable, and it consists of cladding and core.

19. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 19 5.1.3 Fiber-Optic Cable Fiber-Optic Cable Connectors  the subscriber channel (SC) connector is used for cable TV  the straight-tip (ST) connector is used for connecting cable to networking devices.  MT-RJ is a connector that is the same size as RJ 45.

20. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 20 5.1.3 Fiber-Optic Cable Performance  attenuation is flatter than in the case of twisted-pair cable and coaxial cable  fewer (10 times less) repeaters are needed when using the fiber-optic cable.

21. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 21 5.1.3 Fiber-Optic Cable Applications  often used in backbone networks because of its wide bandwidth is cost-effective.  with wavelength-division multiplexing (WDM), data can be transferred at data rate of 1600 Gbps.  LANs such as 100Base-FX network (Fast Ethernet) and 1000Base-X Advantages  Higher bandwidth  Less signal attenuation  Immunity to electromagnetic interference  Resistance to corrosive materials  Light weight  Greater immunity to tapping

22. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 22 5.1.3 Fiber-Optic Cable Disadvantages  Installation and maintenance  Unidirectional light propagation  High cost

23. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 23 5.2 Unguided Media : Wireless unguided media transport electromagnetic waves without using a physical conductor – wireless communication. signals broadcasted through free space and thus available to anyone who has a device capable of receiving them. electromagnetic spectrum for wireless communication :

24. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 24 5.2 Unguided Media : Wireless Propagation methods

25. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 25 5.2 Unguided Media : Wireless Bands of frequency for various communications

26. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 26 5.2 Unguided Media : Wireless wireless transmission can be divided into three broad groups :

27. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 27 5.2.1 Radio Wave transmission radio waves : waves ranging between 3 kHz and 1 GHz microwaves : waves ranging between 1 and 300 GHz has a character of omnidirectional – propagate in all directions  advantage : sending and receiving antenna do not have to be aligned.  disadvantage : radio waves transmitted by one antenna are susceptible to interference by another antenna that may send signals using the same frequency or band. radio waves that propagate in the sky mode can travel a long distance the radio waves band is relatively narrow (below 1 GHz) – when divided into sub-bands becomes narrower – lead to a low data rate for digital communications

28. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 28 5.2.1 Radio Wave transmission Omnidirectional Antenna  antenna that send out signals in all direction.  there are several type of omnidirectional antenna based on wavelength, strength, and the purpose of transmission.  omnidirectional characteristic of radio waves make them useful for multicasting – one sender and many receivers.  ex : AM/FM radio, television, maritime radio, cordless phones, paging

29. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 29 5.2.2 Microwaves frequencies between 1 and 300 GHz unidirectional – microwaves can directly focused to the receiving antenna other characteristics :  line-of-sight propagation : antenna need to be in direct sight of each other (not suitable for long distance propagation)  very high-frequency microwaves cannot penetrate walls  relatively wideband (1GHz – 300 GHz) : wider sub-bands can be assigned, and high data rate is possible  use of certain portions of the band requires permission from the authorities Unidirectional antenna  microwaves need unidirectional antenna that sends waves in one direction  e.g. dish antenna, horn antenna

30. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 30 5.2.2 Microwaves Unidirectional antenna application  very useful in unicast (one-to-one) communication  e.g. cellular phone, satellite networks and wireless LANs

31. Chapter 5 : Transmission Media BENG 4522 Data Communications & Computer Networks 31 5.2.3 Infrared frequencies from 300 GHz to 400 THz (wavelengths from 1 mm – 770 nm) used for short range communication very high-frequency cannot penetrate walls – prevent interference between systems at different room or indoor space useless for long range communications cannot be used outside building due to interference form the sun ray’s infrared waves Applications  the very wide band (almost 400 THz) gives an excellent potential for data transmission  used to transmit digital data at very high data rate  Infrared Data Association (IrDA) – establish a standards for using infrared signals for communications between devices such as keyboards, mice, PCs, printer etc  e.g. standard for wireless keyboard – 4 Mbps for a distance up to 8 mm