1. 1 Kyung Hee University Prof. Choong Seon HONG Multiplexing

2. 2 Kyung Hee University 8 장 다중화 (Multiplexing) 8.1 Many to One/One to Many 8.2 Type of Multiplexing 8.3 Multiplexing Application : Telephone system

3. 3 Kyung Hee University 다중화 (Multiplexing)  다중화 (Multiplexing)  is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.

4. 4 Kyung Hee University 다중화 (Multiplexing)  Multiplexing vs. No Multiplexing

5. 5 Kyung Hee University 8.1 Many to One/One to Many  다중화기 (Multiplexer)  transmission streams combine into a single stream(many to one)  역다중화기 (Demultiplexer)  stream separates into its component transmission(one to many) and directs them to their intended receiving devices

6. 6 Kyung Hee University 8.2 Many to One/One to Many  Categories of Multiplexing

7. 7 Kyung Hee University FDM  FDM(Frequency-Division Multiplexing)  is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted

8. 8 Kyung Hee University FDM (cont’d)  FDM process  each telephone generates a signal of a similar frequency range  these signals are modulated onto different carrier frequencies(f1, f2, f3)

9. 9 Kyung Hee University FDM (cont’d)  FDM multiplexing process, time-domain

10. 10 Kyung Hee University FDM(cont’d)  FDM multiplexing process, frequency-domain

11. 11 Kyung Hee University FDM(cont’d)  Demultiplexing  separates the individual signals from their carries and passes them to the waiting receivers.

12. 12 Kyung Hee University FDM(cont’d)  FDM demultiplexing process, time-domain

13. 13 Kyung Hee University FDM(cont’d)  FDM demultiplexing, frequency-domain

14. 14 Kyung Hee University FDM(cont’d)  Example : Cable Television  coaxial cable has a bandwidth of approximately 500Mhz  individual television channel require about 6Mhz of bandwidth for transmission  can carry 83 channels theoretically

15. 15 Kyung Hee University 8.3 Wave Division Multiplexing (WDM)  WDM is conceptually same as FDM  except that the multiplexing and demultiplexing involve light signals transmitted through fiber-optic channels

16. 16 Kyung Hee University WDM (cont’d)  Combining and splitting of light sources are easily handled by a prism  Prism bends a beam of light based on the angle of incidence and the frequency.

17. 17 Kyung Hee University TDM(cont’d)  TDM(Time-Division Multiplexing)  is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving device

18. 18 Kyung Hee University TDM(cont’d)  TDM

19. 19 Kyung Hee University TDM(cont’d)  TDM can be implemented in two ways  Synchronous TDM  Asynchronous TDM

20. 20 Kyung Hee University TDM(cont’d)  Synchronous TDM  the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.

21. 21 Kyung Hee University TDM(cont’d)  Frame  Time slots are grouped into frames  A frame consists of one complete cycle of time slots, including one or more slots dedicated to each sending device, plus framing bits.

22. 22 Kyung Hee University TDM(cont’d)  Synchronous TDM

23. 23 Kyung Hee University TDM(cont’d)  Interleaving  synchronous TDM can be compared to a very fast rotating switch  switch moves from device to device at a constant rate and in a fixed order 6 empty slots out of 24 are being wasted

24. 24 Kyung Hee University TDM(cont’d)  Demultiplexer decomposes each frame by discarding the framing bits and extracting each character in turn  Synchronous TDM, demultiplexing process

25. 25 Kyung Hee University TDM(cont’d)  Framing bits ~ allows the demultiplexer to synchronize with the incoming stream so that it can separate the time slots accurately (ex: 01010101 ….)

26. 26 Kyung Hee University TDM(cont’d)  Synchronous TDM Example 4 characters + 1 framing bit

27. 27 Kyung Hee University TDM(cont’d)  Asynchronous TDM : statistical time-division multiplexing Synchronous or Asynchronous : Not flexible or Flexible

28. 28 Kyung Hee University TDM(cont’d)  Examples of asynchronous TDM frames a. Case 1: Only three lines sending data

29. 29 Kyung Hee University TDM(cont’d) b. Case 2: Only four lines sending data

30. 30 Kyung Hee University TDM(cont’d) c. Case 3: All five lines sending data

31. 31 Kyung Hee University TDM(cont’d)  Inverse Multiplexing  takes the data stream from one high-speed line and breaks it into portion that can be sent across several lower speed lines simultaneously, with no loss in the collective data rate

32. 32 Kyung Hee University TDM(cont’d)  Multiplexing and inverse multiplexing

33. 33 Kyung Hee University TDM(cont’d)  Why do we need inverse multiplexing ?  wants to send data, voice, and video each of which requires a different data rate. [example]  voice - 64 Kbps link  data - 128 Kbps link  video - 1,544 Mbps link

34. 34 Kyung Hee University 8.5 Multiplexing application : Telephone system  Telephone Network

35. 35 Kyung Hee University Multiplexing application(cont’d)  Common Carrier Services

36. 36 Kyung Hee University Multiplexing application(cont’d)  Analog Service

37. 37 Kyung Hee University Multiplexing application(cont’d)  Analog Switched Service ~ is the familiar dial-up service most often encountered when using a home telephone (PSTN : Public Switched Telephone Network)  local loop : connection from the subscriber’s handset to the network

38. 38 Kyung Hee University Multiplexing application(cont’d)  Analog Leased Service : dedicated line ~ offers customers the opportunity to lease line(dedicated line), that is permanently connected to another customer.  No dialing is needed

39. 39 Kyung Hee University Multiplexing application(cont’d)  Analog Hierarchy  To maximize the efficiency of their infrastructure, telephone companies have traditionally multiplexed signals from lower bandwidth lines onto higher bandwidth lines.

40. 40 Kyung Hee University Multiplexing application(cont’d)  Analog hierarchy

41. 41 Kyung Hee University Multiplexing application(cont’d)  Digital Services  advantage - less sensitive than analog service to noise - lower cost

42. 42 Kyung Hee University Multiplexing application(cont’d)  Categories of digital service

43. 43 Kyung Hee University Multiplexing application(cont’d)  Switched/56 service ~ is the digital version of an analog switched line ~ allows data rates of up to 56Kbps

44. 44 Kyung Hee University Multiplexing application(cont’d)  DDS(Digital Data Service) ~ is the digital version of an analog leased line (maximum speed : 56Kbps)

45. 45 Kyung Hee University Multiplexing application(cont’d)  DS(Digital Signal) Service ~ is a hierarchy of digital signal

46. 46 Kyung Hee University Multiplexing application(cont’d)  DS Service  DS-0 : single digital channel of 64Kbps  DS-1 : 1,544Mbps, 24 개의 64Kbps + 8Kbps 의 overhead  DS-2 : 6,312Mbps, 96 개의 64Kbps+168Kbps 의 overhead  DS-3 : 44,376Mbps, 672 개의 64Kbps+1.368Mbps 의 overhead  DS-4 : 274,176Mbps,4032 개의 64Kbps+16.128Mbps 의 overhead

47. 47 Kyung Hee University Multiplexing application(cont’d)  T Lines ServiceLineRate(Mbps)Voice Channels DS-1 DS-2 DS-3 DS-4 T-1 T-2 T-3 T-4 1,544 6,312 44,736 274,176 24 96 672 4032

48. 48 Kyung Hee University Multiplexing application(cont’d)  T lines for Analog Transmission

49. 49 Kyung Hee University Multiplexing application(cont’d)  T-1 frame structure

50. 50 Kyung Hee University Multiplexing application(cont’d)  Fractional T Lines DSU/CSU (Data Service Unit / Channel Service Unit)

51. 51 Kyung Hee University Multiplexing application(cont’d)  E Lines  Europeans use a version of T lines called E lines Service Rate(Mbps) Voice Channels E-1 E-2 E-3 E-4 2,048 8,448 34,368 139,264 30 120 480 1920

52. 52 Kyung Hee University Multiplexing application(cont’d)  Other Multiplexing Service  ISDN(Integrated Services Digital Network)  SONET(Synchronous Optical Network)  ATM(Asynchronous Transfer Mode)

53. 53 Kyung Hee University 8.6 Digital Subscriber Line (DSL)  uses a newer technology that used the existing telecommunications networks such as the local loop telephone line  Asymmetric Digital Subscriber Line (ADSL)  provides higher bit rates in the downstream direction (from the telephone central office to the subscriber’s site) than the upstream direction  divides the bandwidth of a twisted-pair cable (one megahertz) into three bands

54. 54 Kyung Hee University DSL (cont’d)  Modulation Techniques  CAP (carrierless amplitude/phase) l similar to QAM l carrier signal is eliminated  DMT (discrete multitone technique) l combines QAM and FDM l the available bandwidth for each direction is divided into 4Khz channels, each having its own carrier frequency

55. 55 Kyung Hee University DSL (cont’d)  The concept of DMT with N channels

56. 56 Kyung Hee University DSL (cont’d)  ANSI standard defines a rate of 60 Kbps for each 4-Khz channel, which means a QAM modulation with 15 bits per baud l The upstream channel usually occupies 25 channels (60kbps x 20 = 1.5 Mbps) l The downstream channel usually occupies 200 channels (200 x 60Kbps = 12 Mbps) – But, the bit rate in this direction ranges from 500 Kbps to 8 Mbps due to noise

57. 57 Kyung Hee University DSL (cont’d)  ADSL and the bit rates in each direction

58. 58 Kyung Hee University DSL (cont’d)  RADSL (Rate Adaptive Digital Subscriber Line)  allows different data rates depending on the type of communication : voice, data, multimedia, and so on.  Differing rates may also be assigned to subscribers based on their demand of the bandwidth.  HDSL (High bit rate digital subscriber line)  was designed by Bellcore (now Telcordia) as an alternative to the T-1 (1.544 Mbps)  T1 line uses AMI encoding, but HDSL uses 2B1Q encoding, which is less susceptible to attenuation  A data rate of almost 2 Mbps can be achieved without repeaters up to a distance of 3.6 km  uses two twisted-pair wires to achieve full-duplex transmission

59. 59 Kyung Hee University DSL (cont’d)  SDSL (symmetric digital subscriber line)  is same as HDSL but uses one single twisted-pair cable  achieves the same data rate as HDSL  echo cancellation technique is employed to create a full-duplex transmission  VDSL (very high bit rate digital subscriber line)  an alternative approach that is similar to ADSL  uses coaxial, fiber-optic, or twisted-pair cable for short distances (300 to 1800 meters)  modulation technique is DMT with a bit rate of 50 to 55 Mbps downstream and 1.5 to 2.5 Mbps upstream

60. 60 Kyung Hee University 8.7 FTTC  Optical fiber has noise resistance and high bandwidth capacity, but every expensive  Fiber to the curb (FTTC)  Optical fiber is the medium from the central office of the telephone office or from the head office of a cable company  The medium from the curb to the subscriber premise is the less expensive twisted-pair or coaxial cable  Optical signals at the switching station are multiplexed, using WDM

61. 61 Kyung Hee University FTTC (cont’d)  FTTC in the telephone network

62. 62 Kyung Hee University FTTC (cont’d)  FTTC in the cable TV network