1. Electromagnetic Signals zFunction of time yAnalog (varies smoothly over time) yDigital (constant level over time, followed by a change to another level) zFunction of frequency ySpectrum (range of frequencies) yBandwidth (width of the spectrum)

2. Periodic Signal Characteristics yAmplitude (A): signal value, measured in volts yFrequency (f): repetition rate, cycles per second or Hertz yPeriod (T): amount of time it takes for one repetition, T=1/f yPhase (Φ): relative position in time, measured in degrees

3. time (sec) amplitude (volts) 1 cycle frequency (hertz) = cycles per second phase difference Analog Signaling zrepresented by sine waves

4. Digital Signaling zrepresented by square waves or pulses time (sec) amplitude (volts) 1 cycle frequency (hertz) = cycles per second

5. Digital Text Signaling zTransmission of electronic pulses representing the binary digits 1 and 0 zHow do we represent letters, numbers, characters in binary form? zEarliest example: Morse code (dots and dashes) zMost common current form: ASCII

6. ASCII Character Codes zUse 8 bits of data (1 byte) to transmit one character z8 binary bits has 256 possible outcomes (0 to 255) zRepresents alphanumeric characters, as well as “special” characters

7. Digital Image Signaling z Pixelization and binary representation Code: 00000000 00111100 01110110 01111110 01111000 01111110 00111100 00000000

8. Why Study Analog? zTelephone system is primarily analog rather than digital (designed to carry voice signals) zLow-cost, ubiquitous transmission medium zIf we can convert digital information (1s and 0s) to analog form (audible tone), it can be transmitted inexpensively

9. Voice Signals zEasily converted from sound frequencies (measured in loudness/db) to electromagnetic frequencies, measured in voltage zHuman voice has frequency components ranging from 20Hz to 20kHz zFor practical purposes, the telephone system has a narrower bandwidth than human voice, from 300 to 3400Hz

10. Bandwidth zWidth of the spectrum of frequencies that can be transmitted yif spectrum=300 to 3400Hz, bandwidth=3100Hz zGreater bandwidth leads to greater costs zLimited bandwidth leads to distortion zAnalog measured in Hertz, digital measured in baud

11. BPS vs. Baud zBPS=bits per second zBaud=# of signal changes per second zEach signal change can represent more than one bit, through variations on amplitude, frequency, and/or phase

12. Transmission Media zthe physical path between transmitter and receiver zdesign factors ybandwidth yattenuation: weakening of signal over distances yinterference: ynumber of receivers

13. Impairments and Capacity zImpairments exist in all forms of data transmission zAnalog signal impairments result in random modifications that impair signal quality zDigital signal impairments result in bit errors (1s and 0s transposed)

14. Transmission Impairments zAttenuation yloss of signal strength over distance zAttenuation Distortion ydifferent losses at different frequencies zDelay Distortion ydifferent speeds for different frequencies zNoise

15. Types of Noise zThermal (aka “white noise”) yUniformly distributed, cannot be eliminated zIntermodulation ywhen different frequencies zCrosstalk zImpulse noise yLess predictable

16. Transmission Media ztwo major classes yconducted or guided media xuse a conductor such as a wire or a fiber optic cable to move the signal from sender to receiver ywireless or unguided media xuse radio waves of different frequencies and do not need a wire or cable conductor to transmit signals

17. Guided Transmission Media zthe transmission capacity depends on the distance and on whether the medium is point-to-point or multipoint ze.g., ytwisted pair wires ycoaxial cables yoptical fiber

18. Twisted Pair Wires zconsists of two insulated copper wires arranged in a regular spiral pattern to minimize the electromagnetic interference between adjacent pairs zoften used at customer facilities and also over distances to carry voice as well as data communications zlow frequency transmission medium

19. Twisted Pair Wires ztwo varieties ySTP (shielded twisted pair) xthe pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic interference yUTP (unshielded twisted pair) xeach wire is insulated with plastic wrap, but the pair is encased in an outer covering

20. Twisted Pair Wires zCategory 3 UTP ydata rates of up to 16mbps are achievable zCategory 5 UTP ydata rates of up to 100mbps are achievable ymore tightly twisted than Category 3 cables ymore expensive, but better performance zSTP yMore expensive, harder to work with

21. Twisted Pair Advantages zinexpensive and readily available zflexible and light weight zeasy to work with and install

22. Twisted Pair Disadvantages zsusceptibility to interference and noise zattenuation problem yFor analog, repeaters needed every 5-6km yFor digital, repeaters needed every 2-3km zrelatively low bandwidth (3000Hz)

23. Coaxial Cable (or Coax) zbandwidth of up to 400 MHz zhas an inner conductor surrounded by a braided mesh zboth conductors share a common center axial, hence the term “co-axial”

24. Coax Layers copper or aluminum conductor insulating material shield (braided wire) outer jacket (polyethylene)

25. Coax Advantages zhigher bandwidth y400 to 600Mhz yup to 10,800 voice conversations zcan be tapped easily (pros and cons) zmuch less susceptible to interference than twisted pair

26. Coax Disadvantages zhigh attenuation rate makes it expensive over long distance zbulky

27. Fiber Optic Cable zrelatively new transmission medium used by telephone companies in place of long- distance trunk lines zalso used by private companies in implementing local data communications networks zrequire a light source with injection laser diode (ILD) or light-emitting diodes (LED)

28. plastic jacketglass or plastic cladding fiber core Fiber Optic Layers zconsists of three concentric sections

29. Fiber Optic Types zmultimode step-index fiber ythe reflective walls of the fiber move the light pulses to the receiver zmultimode graded-index fiber yacts to refract the light toward the center of the fiber by variations in the density zsingle mode fiber ythe light is guided down the center of an extremely narrow core

30. fiber optic multimode step-index fiber optic multimode graded-index fiber optic single mode Fiber Optic Signals

31. Fiber Optic Advantages zgreater capacity (bandwidth of up to 2 Gbps) zsmaller size and lighter weight zlower attenuation zimmunity to environmental interference zhighly secure due to tap difficulty and lack of signal radiation

32. Fiber Optic Disadvantages zexpensive over short distance zrequires highly skilled installers zadding additional nodes is difficult

33. Wireless (Unguided Media) Transmission ztransmission and reception are achieved by means of an antenna zdirectional ytransmitting antenna puts out focused beam ytransmitter and receiver must be aligned zomnidirectional ysignal spreads out in all directions ycan be received by many antennas

34. Wireless Examples zterrestrial microwave transmission zsatellite transmission zbroadcast radio zinfrared

35. Terrestrial Microwave Transmission zuses the radio frequency spectrum, commonly from 2 to 40 Ghz ztransmitter is a parabolic dish, mounted as high as possible zused by common carriers as well as by private networks zrequires unobstructed line of sight between source and receiver zcurvature of the earth requires stations (called repeaters) to be ~30 miles apart

36. Microwave Transmission Applications zlong-haul telecommunications service for both voice and television transmission zshort point-to-point links between buildings for closed-circuit TV or a data link between LANs zbypass application

37. Microwave Transmission Advantages zno cabling needed between sites zwide bandwidth zmultichannel transmissions

38. Microwave Transmission Disadvantages zline of sight requirement zexpensive towers and repeaters zsubject to interference such as passing airplanes and rain

39. Satellite Microwave Transmission za microwave relay station in space zcan relay signals over long distances zgeostationary satellites yremain above the equator at a height of 22,300 miles (geosynchronous orbit) ytravel around the earth in exactly the time the earth takes to rotate

40. Satellite Transmission Links zearth stations communicate by sending signals to the satellite on an uplink zthe satellite then repeats those signals on a downlink zthe broadcast nature of the downlink makes it attractive for services such as the distribution of television programming

41. dish uplink stationdownlink station satellite transponder 22,300 miles Satellite Transmission Process

42. Satellite Transmission Applications ztelevision distribution ya network provides programming from a central location ydirect broadcast satellite (DBS) zlong-distance telephone transmission yhigh-usage international trunks zprivate business networks

43. Principal Satellite Transmission Bands zC band: 4(downlink) - 6(uplink) GHz ythe first to be designated zKu band: 12(downlink) -14(uplink) GHz yrain interference is the major problem zKa band: 19(downlink) - 29(uplink) GHz yequipment needed to use the band is still very expensive

44. Satellite Advantages zcan reach a large geographical area zhigh bandwidth zcheaper over long distances

45. Satellite Disadvantages zhigh initial cost zsusceptible to noise and interference zpropagation delay

46. Common Carriers za government-regulated private company zinvolved in the sale of infrastructure services in transportation and communications zrequired to serve all clients indiscriminately zservices and prices from common carriers are described in tariffs

47. Leased (or Dedicated) Lines zpermanently or semi-permanently connect between two points zeconomical in high volume calls between two point zno delay associated with switching times zcan assure consistently high-quality connections

48. Leased (or Dedicated) Lines zvoice grade channels ynormal telephone lines yin the range of 300 Hertz to 3300 Hertz zconditioning or equalizing yreduces the amount of noise on the line, providing lower error rates and increased speed for data communications

49. T-1 Carrier zalso referred to as DS-1 signaling zprovides digital full-duplex transmission rates of 1.544Mbps zusually created by multiplexing 24 64- Kbps voice or 56-Kbps data lines zhigher speeds are available with T-3 (45Mbps) and T-4 services (274Mbps) zin Europe, E-1 (2.048Mbps) is used instead of T-1

50. Integrated Services Digital Network (ISDN) zall-digital transmission facility that is designed to replace the analog PSTN zbasic ISDN (basic rate access) ytwo 64Kbps bearer channels + 16Kbps data channel (2B+D) = 144 Kbps zbroadband ISDN (primary rate access) ytwenty-three 64Kbps bearer channels + 64 data channel (23B+D) = 1.536 Mbps

51. Past Criticism of ISDN z“Innovations Subscribers Don’t Need” z“It Still Doesn’t Network” z“It Still Does Nothing” zWhy so much criticism? yoverhyping of services before delivery yhigh price of equipment ydelay in implementing infrastructure yincompatibility between providers' equipment.

52. ISDN Channel Definitions zB (bearer) channels y64 kbps channels that may be used to carry voice, data, facsimile, or image zD (demand) channels ymainly intended for carrying signaling, billing and management information to control ISDN services (out-of-band control messages) ymay be either 16 or 64 kbps

53. Two Levels of ISDN Service zbasic rate interface (BRI) y2B (64 kbps) + D (16 kbps) = 144 kbps zprimary rate interface (PRI) y23B (64 kbps) + D (64 kbps) = 1.536 Mbps xNorth American standard y30B (64 kbps) + D (64 kbps) = 1.984 Mbps xEuropean standard