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Telecommunication Technologies

Telecommunication Technologies. Week 10 Interfacing. Interfacing. Characteristics of Interface. Mechanical Connection plugs Electrical Voltage, timing, encoding Functional Data, control, timing, grounding Procedural Sequence of events. Mechanical Specification. 1. 0.

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Telecommunication Technologies

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  1. Telecommunication Technologies Week 10 Interfacing

  2. Interfacing EIE325: Telecommunication Technologies

  3. Characteristics of Interface • Mechanical • Connection plugs • Electrical • Voltage, timing, encoding • Functional • Data, control, timing, grounding • Procedural • Sequence of events EIE325: Telecommunication Technologies

  4. Mechanical Specification

  5. 1 0 Electrical Specification +3V ?????? -3V EIE325: Telecommunication Technologies

  6. Functional Specification • Various functional tasks of interchange circuits • data (4) • control (16) • transmission (13) • loopback testing (3) • timing (3) • ground EIE325: Telecommunication Technologies

  7. Loopback testing • Provide testing of DCE • Fault isolation • Common on modern modems • Output connected to input – isolated from the transmission line • Remote or Local loopback EIE325: Telecommunication Technologies

  8. Local and Remote Loopback EIE325: Telecommunication Technologies

  9. The interchange circuits EIE325: Telecommunication Technologies

  10. Transmission on secondary channel Transmission on primary channel Loopback

  11. The interchange circuits EIE325: Telecommunication Technologies

  12. Procedural Specification • Defines the sequence of operation, correct request/response sequences and requirements to send and receive data EIE325: Telecommunication Technologies

  13. Asynchronous private line modem Connecting two DTE over a short distance Only six circuits required AB: Ground (102) BA: Transmit (103) BB: Receive (104) CA: Request to Send (105) CB: Clear to Send (106) CC: DCE ready (107) CF: Received line signal detector (109) A Modem EIE325: Telecommunication Technologies

  14. A Modem • When turned on and ready, modem (DCE) asserts DCE ready (CC) • When DTE ready to send data, it asserts Request to Send (CA) • Also inhibits receive mode in half duplex • Modem responds when ready by asserting Clear to send (CB) • DTE sends data (BA) • When data arrives (BB), local modem asserts Receive Line Signal Detector (CF) and delivers data EIE325: Telecommunication Technologies

  15. Public line modem • Previous example is insufficient for modem operating on public network • Also need • CD: DTE ready (108.2) • CE: Ring Indicator (125) EIE325: Telecommunication Technologies

  16. Dial Up Operation EIE325: Telecommunication Technologies

  17. Dial Up Operation EIE325: Telecommunication Technologies

  18. Dial Up Operation EIE325: Telecommunication Technologies

  19. HDLC example

  20. EIE325: Telecommunication Technologies

  21. Null Modem • For direct communication between peer DTE (no DCE!)

  22. Telecommunication Technologies Week 10 Multiplexing

  23. Multiplexing EIE325: Telecommunication Technologies

  24. Multiplexing • Frequency Division Multiplexing • Wavelength Division Multiplexing • Time Division Multiplexing • Synchronous TDM • Statistical TDM • Code Division Multiplexing EIE325: Telecommunication Technologies

  25. Frequency Division Multiplexing EIE325: Telecommunication Technologies

  26. Frequency Division Multiplexing (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) • NB: Channel allocated even if no data • e.g. broadcast radio EIE325: Telecommunication Technologies

  27. FDM of Three Voiceband Signals

  28. FDM System: Transmitter

  29. FDM System: Transmission

  30. FDM System: Receiver

  31. Example: Analog Carrier Systems • AT&T (USA) • Hierarchy of FDM schemes • Group • 12 voice channels (4kHz each) = 48kHz • Range 60kHz to 108kHz • Supergroup • 60 channel • FDM of 5 group signals on carriers between 420kHz and 612 kHz • Mastergroup • 10 supergroups EIE325: Telecommunication Technologies

  32. Asymmetrical Digital Subscriber Line • ADSL • Link between subscriber and network • Local loop • Uses currently installed twisted pair cable • Can carry broader spectrum • 1 MHz or more EIE325: Telecommunication Technologies

  33. ADSL Design • Asymmetric • Greater capacity downstream than upstream • Frequency division multiplexing • Lowest 25kHz for voice • Plain old telephone service (POTS) • Use echo cancellation or FDM to give two bands • Use FDM within bands • Range 5.5km EIE325: Telecommunication Technologies

  34. ADSL Channel Configuration EIE325: Telecommunication Technologies

  35. xDSL • High data rate DSL (HDSL) • 2Mbps over two twisted pair lines • BW of less than 200kHz • Single line DSL (SDSL) • Single twisted pair • Echo cancellation • Very high data rate DSL (VDSL) • New: increase data rate at the expense of distance EIE325: Telecommunication Technologies

  36. Time Division Multiplexing EIE325: Telecommunication Technologies

  37. TDM System

  38. TDM: Transmitter EIE325: Telecommunication Technologies

  39. TDM: Transmission EIE325: Telecommunication Technologies

  40. TDM: Receiver EIE325: Telecommunication Technologies

  41. Synchronous Time Division Multiplexing • Data rate of medium exceeds data rate of digital signal to be transmitted • Multiple digital signals interleaved in time • May be at bit level of 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 EIE325: Telecommunication Technologies

  42. Synchronous TDM

  43. 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 full • Data rate on line lower than aggregate rates of input lines EIE325: Telecommunication Technologies

  44. Statistical TDM

  45. Expected Link Usage (kbps) 9am – 5pm 5pm – 1am 1am – 9am HK trading line 12 1 3 London trading line 5 19 3 New York trading line 1 4 21 An international brokerage firm has its head office in Hong Kong, and a smaller branch office in Singapore. The firm's interests lie in trading on the futures markets of Hong Kong, London, and New York; and data related to these trades should be communicated over a private leased line between Hong Kong and Singapore. The company finds that a single leased line between Hong Kong and Singapore is insufficient for its needs. Instead, the Hong Kong, London and New York trading arms each maintain a separate link and these three lines are multiplexed together for transmission between Hong Kong and Singapore. Each of these three lines is utilised 24 hours per day, but varies according to the following table: Compute the capacity required on the multiplexed line using: (i) synchronous time division multiplexing. (ii) statistical time division multiplexing if 5% of capacity is required for framing overhead.

  46. Synchronous vs. Statistical TDM EIE325: Telecommunication Technologies

  47. TDM Link Control • No headers and tails • Data link control protocols not needed • Flow control • Data rate of multiplexed line is fixed • If one channel receiver cannot receive data, the others must carry on • The corresponding source must be quenched • This leaves empty slots • Error control • Errors are detected and handled by individual channel systems EIE325: Telecommunication Technologies

  48. Data Link Control on TDM Inputs: Transmission:

  49. Framing • No flag or SYNC characters bracketing TDM frames • Must provide synchronising 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 EIE325: Telecommunication Technologies

  50. Pulse Stuffing • Problem - Synchronising 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 EIE325: Telecommunication Technologies

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