Chapter 8 - Multiplexing 9e

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  • 1. Multiplexing CEN 220/CIS 192 Advanced Data Communications and Networking Data and Computer Communications, W. Stallings 9/E, Chapter 8
  • 2. 2 Multiplexing “It was impossible to get a conversation going, everybody was talking too much.” —Yogi Berra
  • 3. 3 Multiplexing multiple links on 1 physical line common on long-haul, high capacity, links have FDM, TDM, STDM alternatives
  • 4. 4 Frequency Division Multiplexing (FDM)
  • 5. 5 FDM System Overview
  • 6. 6 FDM Voiceband Example
  • 7. 7 Analog Carrier Systems long-distance links use an FDM hierarchy AT&T (USA) and ITU-T (International) variants Group  12 voice channels (4 kHz each) = 48 kHz  Range 60 kHz to 108 kHz Supergroup  FDM of 5 group signals supports 60 channels  carriers between 420 kHz and 612 kHz Mastergroup  FDM of 10 supergroups supports 600 channels original signal can be modulated many times
  • 8. 8 North American and International FDM Carrier Standards
  • 9. 9 Wavelength Division Multiplexing (WDM)
  • 10. 10 ITU WDM Channel Spacing (G.692)
  • 11. 11 Synchronous Time Division Multiplexing
  • 12. 12 TDM System Overview
  • 13. 13 TDM Link Control no headers and trailers data link control protocols not needed flow control  data rate of multiplexed line is fixed  if one channel receiver can not receive data, the others must carry on  corresponding source must be quenched  leaving empty slots error control  errors detected & handled on individual channel
  • 14. 14 Data Link Control on TDM
  • 15. 15 Framing no flag or SYNC chars bracketing TDM frames must still provide synchronizing mechanism between source and destination clocks added digit framing is most common  one control bit added to each TDM frame  identifiable bit pattern used as control channel  alternating pattern 101010…unlikely to be sustained on a data channel  receivers compare incoming bits of frame position to the expected pattern
  • 16. 16 Pulse Stuffing – problem of synchronizing various data sources – variation among clocks could cause loss of synchronization – issue of data rates from different sources not related by a simple rational number
  • 17. 17 TDM Example
  • 18. 18 Digital Carrier Systems
  • 19. 19 North American and International TDM Carrier Standards
  • 20. 20 DS-1 Transmission Format
  • 21. 21 SONET/SDH Synchronous Optical Network (ANSI) Synchronous Digital Hierarchy (ITU-T) high speed capability of optical fiber defines hierarchy of signal rates – Synchronous Transport Signal level 1 (STS-1) or – Optical Carrier level 1 (OC-1) is 51.84 Mbps – carries one DS-3 or multiple (DS1 DS1C DS2) plus ITU-T rates (e.g., 2.048 Mbps) – multiple STS-1 combine into STS-N signal – ITU-T lowest rate is 155.52 Mbps (STM-1)
  • 22. 22 SONET/SDH Signal Hierarchy
  • 23. 23 SONET Frame Format
  • 24. 24 Statistical TDM
  • 25. 25 Statistical TDM Frame Format
  • 26. 26 Single-Server Queues with Constant Service Times and Poisson (Random) Arrivals
  • 27. 27 Cable Modems – dedicate two cable TV channels to data transfer – each channel shared by number of subscribers using statistical TDM
  • 28. 28 Cable Spectrum Division To support both cable television programming and data channels, the cable spectrum is divided in to three ranges:  user-to-network data (upstream): 5 - 40 MHz  television delivery (downstream): 50 - 550 MHz  network to user data (downstream): 550 - 750 MHz
  • 29. 29 Cable Modem Scheme
  • 30. 30 Asymmetrical Digital Subscriber Line (ADSL) link between subscriber and network uses currently installed twisted pair cable is Asymmetric - bigger downstream than up uses Frequency Division Multiplexing  reserve lowest 25 kHz for voice (POTS)  uses echo cancellation or FDM to give two bands has a range of up to 5.5 km
  • 31. 31 ADSL Channel Configuration
  • 32. 32 Discrete Multitone (DMT) multiple carrier signals at different frequencies divide into 4 kHz subchannels test and use subchannels with better SNR 256 downstream subchannels at 4 kHz (60 kbps)  in theory 15.36 Mbps, in practice 1.5-9 Mbps
  • 33. 33 DMT Transmitter
  • 34. 34 Broadband – Customer Side DSL link is between provider and customer a splitter allows simultaneous telephone and data service data services use a DSL modem  sometimes referred to as G.DMT modem DSL data signal can be divided into a video stream and a data stream  the data stream connects the modem to a router which enables a customer to support a wireless local area network
  • 35. 35 Broadband – Provider Side a splitter separates telephone from Internet voice traffic is connected to public switched telephone network (PSTN) data traffic connects to a DSL multiplexer (DSLAM) which multiplexes multiple customer DSL connections to a single high-speed ATM line. ATM line connects ATM switches to a router which provides entry to the Internet
  • 36. 36 xDSL high data rate DSL (HDSL)  2B1Q coding on dual twisted pairs  up to 2Mbps over 3.7km single line DSL  2B1Q coding on single twisted pair (residential) with echo cancelling  up to 2Mbps over 3.7km very high data rate DSL  DMT/QAM for very high data rates  separate bands for separate services
  • 37. 37 Comparison of xDSL Alternatives
  • 38. 38 Summary Multiplexing multiple channels on single link FDM  analog carrier systems  wavelength division multiplexing TDM  TDM link control  pulse stuffing statistical TDM broadband ADSL and xDSL