Transmission Media Codes Prof Aiman Hanna Department of

Transmission Media & Codes © Prof. Aiman Hanna Department of Computer Science Concordia University Montreal, Canada

C onnect then Communicate! u There are many factors that controls how devices should be connected: • • • Cost Capacity of the link / speed Immunity to noise Vulnerability to unauthorized listening (security) Logistics Mobility • Once connected communication is guaranteed. Correct? 2

C onnect then Communicate! (continue. . . ) Digital vs. Analog Signals u Different devices may represent or send information differently u Many devices use digital signals (1 or 0 bit), while others use analog signals (varying voltage) u Conversion between digital and analog is possible but complex 3

C onnect then Communicate! u u (continue. . . ) Signals travels from one place to another through a transmission media There are 3 types of transmission media: • Conductive metal • Transparent glass strand (optical fiber) • Electromagnetic waves (no physical connection) u Which media to use depends on many factors u Two important measures exist: bit rate and bandwidth 4

u C onnect then Communicate! Bit Rate • • u (continue. . . ) How many bits per second (bps) a link can transmit Rates range from 100 s bps to billions of bps (gigabits) and now pushing for trillion bps (terabit) Bandwidth • • Period: Time needed for a signal to complete one cycle Frequency: Number of cycles per second, measured in Hertz (Hz) f=1/p • For example, if then f = 2 MHz p = 0. 5 microseconds (μsec) • A given medium can accommodate a range of frequency • Bandwidth is the difference between the highest and the lowest possible frequency that can be transmitted • For example, telephone signals can handle frequencies between 300 Hz & 3300 Hz; the bandwidth is hence 3000 Hz • In other words, very high or very low audible sounds cannot pass though the telephone Figure 2. 2 - Periodic Signal 5

C onductive Metal u Made of metals such as copper or iron Examples include twisted wire pair and coaxial cable u Twisted Pair: u • • • One of the oldest media; used for the telegraph Basically a circuit of power source, switch & sensor Closing the switch allows current to run and the sensor to click Information on 2 -way telegraph can be found at: http: //hypertextbook. com/facts/2005/telegraph. shtml 6

C onductive Metal u Twisted Pair (continue. . . ) (continue): • Copper is usually used due to its less resistance to electricity, as well as high resistance to corrosion • Twisted wires use balanced signals; 180 o out of phase • More twists reduce crosstalk, the electromagnetic interference between adjacent pairs 7

C onductive Metal u Twisted Pair (continue. . . ) (continue): • Although copper has less resistance to electricity, signal will eventually die (attenuate) • Repeaters are used to solve this problem • Two types of twisted pair wires exist: Unshielded & Shielded; they have different cost & quality Figure 2. 4 – Two Points Connected using a Repeater 8

C onductive Metal u (continue. . . ) Coaxial Cable: • Typically transmits information in either baseband or broadband mode • With baseband, the cable bandwidth is devoted to a single stream of data; this is typical in LANs • With broadband, the BW is divided into ranges; each range carries separate code information • Cable TVs use broadband coaxial cable Figure 2. 5 – Coaxial Cable 9

C onductive Metal u Coaxial Cable (continue. . . ) (continue): • Two types of coaxial cable exist: Thick. Net and Thin. Net • Coaxial cables accommodate a higher BW and better error rate than twisted pair, however it is more costly 10

O ptical Fiber u There are several problems with conductive metals: • Electrical signals are susceptible to external interference, such as electric motors, lightening, … • Weight; cables are heavy and bulky u Optical fiber is an alternative to conductive metal 11

O ptical Fiber u u u (continue. . . ) Optical fiber uses light, not electricity, to transmit information Impervious to electrical noise and capable of transmitting enormous amount of information Very thin compared to cables; they can be bundled together 12

O ptical Fiber (continue. . . ) Figure 2. 6 – Light Refraction & Reflection Figure 2. 7 – Step-Index Multimode fiber 13

O ptical Fiber (continue. . . ) Figure 2. 8 – Graded-Index Multimode Fiber Figure 2. 9 – Single-Mode Fiber 14

O ptical Fiber u u (continue. . . ) Optical fiber have many advantages of over conducting metal: On the other hand, • They require that electrical signals must be converted first to light and converted back at the other end • Must be handled with great care; some of these fibers could be a thin as human hair 15

W ireless Communications u u u Physical communication is acceptable in many, but not all, situations Wireless communication is an alternative It involves the sending of electromagnetic waves The signal is then received by a receiving antenna Broadcast radio & TV transmit signal this way 16

W ireless Communications (continue. . . ) Figure 2. 10 – Electromagnetic Wave Spectrum Wavelength = Speed of Light / Frequency u u u Low–frequency (high-wavelength) waves traverse very long distances without much loss They also require a very long antenna, which even today may represent a health hazard There are three important types of wireless communication: • • • Microwave Satellite Infrared 17

W ireless Communications u (continue. . . ) Microwave Transmissions • Typically occur between two ground towers • Travel in a straight line – does not follow earth’s curvature • Cannot travel through solid objects Figure 2. 11 – Parabolic Dish Receiving Signals 18

W ireless Communications u (continue. . . ) Microwave Transmissions • Often through Horn Antenna • Towers are used as repeaters to solve earth curvature’s and signal loss problems Figure 2. 13 – Horn Antenna Figure 2. 14 – Microwave Towers as Repeaters 19

W ireless Communications u (continue. . . ) Satellite Transmissions • A science fiction in 1945; A common science today! • Primarily, it is a microwave transmission in which one of the towers is a satellite • In 1957, the Soviet Union launched the Sputnik Figure 2. 15 – Satellite Communications 20

W ireless Communications u (continue. . . ) Satellite Transmissions • Now, how can a satellite remain in a fixed position? 2 3 • Kepler’s law is used: P = KD where: - P is time period needed to rotate around planetary body, - D is the distance between the satellite and the planet’s center. The higher D is the longer it takes for a full rotation - K is a constant - Now, at what height a satellite will have a 24 h period ( P)? - According to Kepler’s Law, the answer is K = 22, 300 miles - above the equator Geosynchronous Orbit Three satellites can almost cover the entire earth 21

W ireless Communications u (continue. . . ) Satellite Transmissions Figure 2. 16 – Satellites in Geosynchronous Orbit 22

W ireless Communications u (continue. . . ) Satellite Transmissions Figure 2. 17 – Atmospheric Interference as a function of angle of transmission 23

W ireless Communications u (continue. . . ) Satellite Transmissions • Satellites must be located apart from each other (with a minimal angel) • Transmission should also be restricted to a specific angel Figure 2. 18 – Satellite receiving more than one signal 24

W ireless Communications u (continue. . . ) Satellite Transmissions • Now, there is no interference. Good! But what about legality? Figure 2. 19 – Satellites receiving one signal 25

W ireless Communications u (continue. . . ) Satellite Transmissions • Some applications, such as military surveillance, require that the satellite does not remain in a fixed position • Low Earth Orbit Satellites can still be used for communication. How? Figure 2. 20 – Ground station communicating with LEO satellites 26

W ireless Communications u (continue. . . ) Satellite Transmissions • • Using many LEO that can directly communicate with each other would enable any two locations in the planet to be connected This however has not fully been implemented yet The LLC project by Motorola Another player is the Teledesic Corporation – 288 satellites (12 groups of 24) – reduced lately to 30 Figure 2. 21 – Two stations communicating via LEO satellites 27

W ireless Communications u (continue. . . ) Satellite Transmissions Teledesic Satellite Constellation of Teledesic Satellites 28

W ireless Communications u (continue. . . ) Wireless LANs • Two technologies used by wireless LANs are Infrared and Radio Waves. Figure 2. 25 – Wireless LAN configuration 29

W ireless Communications u (continue. . . ) Bluetooth • Allows devices that are not considered as typical network devices, such as fridges, microwaves, coffeemakers, …etc. , to communicate • This communication can possibly be between such device and an Internet service 30

W ireless Communications u (continue. . . ) Free Space Optics • Wireless optical technology without the use of a fiber, which is also called as Tera-beam technology • Life. Span Bio. Sciences, Merill Lynch, and others used FSO • Advantage: • Disadvantage: 31

W ireless Communications u (continue. . . ) Does New Technologies obsolete Older ones? • Twisted Pair, Coaxial Cable, Optical Fiber, Microwave, Satellite, Infrared, FSO, . . all coexist • Reasons? 32

u Codes C odes • How is information coded in a format suitable for transmission? u Different codes include: • Morse Code • ASCII (American Standard Code for Information Interchange), 7 -bit code, control characteristics • EBCDIC (Extended Binary Coded Decimal Interchange Code), used for IBM mainframes and peripherals, 8 -bit code, control characters • Baudot code: 5 -bit code for each character. It was designed for the French Telegraph • BCD (Binary Coded Decimal), which was common in many early IBM mainframes • Unicode: New. 16 -bit code independent of language or computer platform. Supports many scripts and mathematical symbols 33

u Codes C odes (continue. . . ) Figure 2. 26 – Transmitting an ASCII Coded Message 34