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COE 341: Data & Computer Communications (T062) Dr. Marwan Abu-Amara. Chapter 8: Multiplexing. Lecture Contents . Introduction Multiplexing Types FDM Synchronous TDM Statistical TDM ADSL. Introduction.

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COE 341: Data & Computer Communications (T062) Dr. Marwan Abu-Amara


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    1. COE 341: Data & Computer Communications (T062)Dr. Marwan Abu-Amara Chapter 8: Multiplexing

    2. Lecture Contents • Introduction • Multiplexing Types • FDM • Synchronous TDM • Statistical TDM • ADSL COE 341 – Dr. Marwan Abu-Amara

    3. Introduction • Multiplexing: A generic term used when more than one application or connection share the capacity of one link • Objective is to achieve better utilization of resources COE 341 – Dr. Marwan Abu-Amara

    4. Multiplexing Types COE 341 – Dr. Marwan Abu-Amara

    5. Frequency Division Multiplexing (FDM) COE 341 – Dr. Marwan Abu-Amara

    6. FDM • Useful bandwidth of medium exceeds required bandwidth of channel • Each signal is modulated to a different carrier frequency • Carrier frequencies separated so signals do not overlap (guard bands) • e.g. broadcast radio • Channel allocated even if no data COE 341 – Dr. Marwan Abu-Amara

    7. FDM COE 341 – Dr. Marwan Abu-Amara

    8. FDM Multiplexing Process: Time-Domain View COE 341 – Dr. Marwan Abu-Amara

    9. FDM Multiplexing Process: Frequency-Domain View COE 341 – Dr. Marwan Abu-Amara

    10. FDM De-Multiplexing Process: Time-Domain View COE 341 – Dr. Marwan Abu-Amara

    11. FDM De-Multiplexing Process: Frequency-Domain View COE 341 – Dr. Marwan Abu-Amara

    12. FDM System – Transmitter COE 341 – Dr. Marwan Abu-Amara

    13. FDM System – Receiver COE 341 – Dr. Marwan Abu-Amara

    14. FDM of Three Voiceband Signals COE 341 – Dr. Marwan Abu-Amara

    15. Analog Carrier Systems • Devised by AT&T (USA) • Hierarchy of FDM schemes • Group • 12 voice channels (4kHz each) = 48kHz • Range 60kHz to 108kHz • Supergroup • 60 channels • FDM of 5 group signals on carriers between 420kHz and 612 kHz • Master group • 10 supergroups • Jumbo group • 6 master groups COE 341 – Dr. Marwan Abu-Amara

    16. Analog FDM Hierarchy COE 341 – Dr. Marwan Abu-Amara

    17. Time Division Multiplexing (TDM) COE 341 – Dr. Marwan Abu-Amara

    18. TDM • Data rate of medium exceeds data rate of digital signal to be transmitted • Multiple digital signals interleaved in time • May be at bit level or blocks • Time slots preassigned to sources and fixed • Time slots allocated even if no data • Time slots do not have to be evenly distributed amongst sources COE 341 – Dr. Marwan Abu-Amara

    19. Time Division Multiplexing COE 341 – Dr. Marwan Abu-Amara

    20. TDM Frames COE 341 – Dr. Marwan Abu-Amara

    21. TDM System – Transmitter COE 341 – Dr. Marwan Abu-Amara

    22. TDM System – Receiver COE 341 – Dr. Marwan Abu-Amara

    23. TDM Link Control • No headers and trailers • Data link control protocols not needed for MUXed line • Flow control • Data rate of multiplexed line is fixed • If one channel receiver can not receive data, the others must carry on • The corresponding source must be halted • This leaves empty slots • Error control • Errors are detected and handled by individual channel systems COE 341 – Dr. Marwan Abu-Amara

    24. Data Link Control on TDM COE 341 – Dr. Marwan Abu-Amara

    25. Framing • So far, no flag or SYNC characters bracketing TDM frames on the MUXed line • Must provide frame synchronizing mechanism • Added digit framing • One control bit added to each TDM frame • Looks like another channel - “control channel” • Identifiable bit pattern used on control channel • e.g. alternating 01010101…unlikely on a data channel • Can compare incoming bit patterns on each channel with sync pattern COE 341 – Dr. Marwan Abu-Amara

    26. Framing in TDM MUXed frame Four data channels C 1 2 3 4 C 1 2 3 4 C 1 0 0 1 ….. Control Channel, C 010101…. ….. A data Channel Unlikelyto have 010101…. over successive frames • RX knows the size of the MUXed frame • It can check each frame bit frame-to-frame for the special pattern until it finds it • Once the position of the control channel is established, RX knows where the channel • sequence starts and sync is established with TX COE 341 – Dr. Marwan Abu-Amara

    27. Pulse Stuffing • Problem - Synchronizing data sources • Clocks in different sources drifting • Data rates from different sources not related by simple rational number • Solution - Pulse Stuffing • Outgoing data rate (excluding framing bits) higher than sum of incoming rates • Stuff extra dummy bits or pulses into each incoming signal until it matches local clock • Stuffed pulses inserted at fixed locations in frame and removed at demultiplexer COE 341 – Dr. Marwan Abu-Amara

    28. TDM of Analog and Digital Sources COE 341 – Dr. Marwan Abu-Amara

    29. Digital Carrier Systems • Hierarchy of TDM (similar to FDM) • USA/Canada/Japan use one system • ITU-T use a similar (but different) system • US system based on DS-1 format • Multiplexes 24 PCM voice channels • Each frame has 8 bits per channel plus one framing bit • 193 bits per frame (24 ch.  8 bits per ch. + 1 framing bit = 193 bits per frame) COE 341 – Dr. Marwan Abu-Amara

    30. DS Signals COE 341 – Dr. Marwan Abu-Amara

    31. DS & T Lines Rates COE 341 – Dr. Marwan Abu-Amara

    32. Digital Carrier Systems • For voice each channel contains one word of digitized data (PCM, 8000 samples per second) • Data rate 8000 x 193 = 1.544Mbps • Five out of six frames have 8 bit PCM samples • Sixth frame is 7 bit PCM word plus signaling bit • Signaling bits form stream for each channel containing control and routing info • Same format for digital data • 23 channels of data • 7 bits per frame plus indicator bit for data or systems control • 24th channel is sync • DS-1 can carry mixed voice and data signals COE 341 – Dr. Marwan Abu-Amara

    33. DS-1 Transmission Format (8000 x 7 bits = 56 kbps) COE 341 – Dr. Marwan Abu-Amara

    34. T1 Due to 1 framing bit Per frame COE 341 – Dr. Marwan Abu-Amara

    35. T1 Frames COE 341 – Dr. Marwan Abu-Amara

    36. E1 COE 341 – Dr. Marwan Abu-Amara

    37. Mixed Data • DS-1 can carry mixed voice and data signals • 24 channels used • No sync byte • Can also interleave DS-1 channels • DS-2 is four DS-1 giving 6.312Mbps COE 341 – Dr. Marwan Abu-Amara

    38. SONET/SDH • Synchronous Optical Network (ANSI) • Synchronous Digital Hierarchy (ITU-T) • Compatible • Utilize the large channel capacity of optical fibers • Signal Hierarchy • Synchronous Transport Signal level 1 (STS-1) or Optical Carrier level 1 (OC-1) • Frame of 810 octets every 125 ms: 51.84Mbps • Carry DS-3 or group of lower rate signals (DS1, DS1C, DS2) plus ITU-T rates (e.g. 2.048Mbps) • Multiple STS-1 combined into STS-N signal • ITU-T lowest rate is 155.52Mbps (STM-1) COE 341 – Dr. Marwan Abu-Amara

    39. SONET/SDH Frame Format COE 341 – Dr. Marwan Abu-Amara

    40. Statistical TDM • In Synchronous TDM many slots are wasted • Statistical TDM allocates time slots dynamically based on demand • Multiplexer scans input lines and collects data until frame is full • Data rate on line lower than aggregate rates of input lines COE 341 – Dr. Marwan Abu-Amara

    41. Statistical TDM COE 341 – Dr. Marwan Abu-Amara

    42. Statistical TDM Frame Formats COE 341 – Dr. Marwan Abu-Amara

    43. Performance • Output data rate less than aggregate input rates • May cause problems during peak periods • Buffer inputs • Keep buffer size to minimum to reduce delay COE 341 – Dr. Marwan Abu-Amara

    44. Buffer Size and Delay • Increasing utilization increases • Buffer size • delay • Utilization > 0.8 is undesirable COE 341 – Dr. Marwan Abu-Amara

    45. ADSL • ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses • The existing local loops can handle bandwidths up to 1.1 MHz • ADSL is an adaptive technology. The system uses a data rate based on the condition of the local loop line • Use the following as a rule of thumb • XYZ km  XYZ Mbps • XYZ km  XYZ Mbps COE 341 – Dr. Marwan Abu-Amara

    46. ADSL Hardware COE 341 – Dr. Marwan Abu-Amara

    47. ADSL Frequency Bands COE 341 – Dr. Marwan Abu-Amara

    48. DMT COE 341 – Dr. Marwan Abu-Amara