Docstoc

Chapter8_Multiplexing_

Document Sample
Chapter8_Multiplexing_ Powered By Docstoc
					                   Multiplexing




             Prof. Choong Seon HONG



Kyung Hee
University
                                      1
                8 장 다중화(Multiplexing)

8.1 Many to One/One to Many

8.2 Type of Multiplexing

8.3 Multiplexing Application : Telephone system




   Kyung Hee
   University
                                                  2
                  다중화(Multiplexing)
다중화(Multiplexing)
   is the set of techniques that allows the simultaneous
    transmission of multiple signals across a single data link.




  Kyung Hee
  University
                                                            3
                  다중화(Multiplexing)
Multiplexing vs. No Multiplexing




   Kyung Hee
   University
                                      4
               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




  Kyung Hee
  University
                                                           5
               8.2 Many to One/One to Many
Categories of Multiplexing




  Kyung Hee
  University
                                             6
                          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




  Kyung Hee
  University
                                                          7
                      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)




  Kyung Hee
  University
                                                          8
                   FDM (cont’d)
FDM multiplexing process, time-domain




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




  Kyung Hee
  University
                                              10
                      FDM(cont’d)
Demultiplexing
   separates the individual signals from their carries and
   passes them to the waiting receivers.




  Kyung Hee
  University
                                                              11
                   FDM(cont’d)
FDM demultiplexing process, time-domain




  Kyung Hee
  University
                                           12
                   FDM(cont’d)
FDM demultiplexing, frequency-domain




  Kyung Hee
  University
                                        13
                      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




  Kyung Hee
  University
                                                       14
        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




  Kyung Hee
  University
                                                          15
                      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.




   Kyung Hee
   University
                                                         16
                      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




  Kyung Hee
  University
                                                          17
              TDM(cont’d)
TDM




 Kyung Hee
 University
                            18
                     TDM(cont’d)
TDM can be implemented in two ways


  Synchronous TDM


  Asynchronous TDM




  Kyung Hee
  University
                                      19
                      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.




  Kyung Hee
  University
                                                             20
                     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.




  Kyung Hee
  University
                                                           21
                   TDM(cont’d)
Synchronous TDM




  Kyung Hee
  University
                                 22
                     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




  Kyung Hee
  University
                                                                23
                     TDM(cont’d)
Demultiplexer decomposes each frame by discarding
 the framing bits and extracting each character in turn

Synchronous TDM, demultiplexing process




   Kyung Hee
   University
                                                          24
                        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 ….)




  Kyung Hee
  University
                                                             25
                 TDM(cont’d)
Synchronous TDM Example
                           4 characters + 1 framing bit




  Kyung Hee
  University
                                                          26
                     TDM(cont’d)
Asynchronous TDM : statistical time-division multiplexing




                  Synchronous or Asynchronous : Not flexible or Flexible
  Kyung Hee
  University
                                                                      27
                     TDM(cont’d)
Examples of asynchronous TDM frames

 a. Case 1: Only three lines sending data




  Kyung Hee
  University
                                            28
                      TDM(cont’d)
b. Case 2: Only four lines sending data




   Kyung Hee
   University
                                          29
                       TDM(cont’d)
c. Case 3: All five lines sending data




   Kyung Hee
   University
                                         30
                      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




  Kyung Hee
  University
                                                            31
                     TDM(cont’d)
Multiplexing and inverse multiplexing




  Kyung Hee
  University
                                         32
                      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



  Kyung Hee
  University
                                                        33
 8.5 Multiplexing application : Telephone system
Telephone Network




  Kyung Hee
  University
                                              34
               Multiplexing application(cont’d)
Common Carrier Services




  Kyung Hee
  University
                                                  35
               Multiplexing application(cont’d)
Analog Service




  Kyung Hee
  University
                                                  36
               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




  Kyung Hee
  University
                                                              37
               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




  Kyung Hee
  University
                                                            38
               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.




  Kyung Hee
  University
                                                         39
                 Multiplexing application(cont’d)
Analog hierarchy




    Kyung Hee
    University
                                                    40
               Multiplexing application(cont’d)
Digital Services
   advantage
       - less sensitive than analog service to noise
       - lower cost




  Kyung Hee
  University
                                                       41
                Multiplexing application(cont’d)
Categories of digital service




   Kyung Hee
   University
                                                   42
               Multiplexing application(cont’d)
Switched/56 service
  ~ is the digital version of an analog switched line
  ~ allows data rates of up to 56Kbps




  Kyung Hee
  University
                                                        43
               Multiplexing application(cont’d)
DDS(Digital Data Service)
  ~ is the digital version of an analog leased line (maximum
    speed : 56Kbps)




  Kyung Hee
  University
                                                           44
               Multiplexing application(cont’d)
DS(Digital Signal) Service
   ~ is a hierarchy of digital signal




  Kyung Hee
  University
                                                  45
               Multiplexing application(cont’d)
DS Service

  DS-0 : single digital channel of 64Kbps

  DS-1 : 1,544Mbps, 24개의 64Kbps + 8Kbps의 overhead

  DS-2 : 6,312Mbps, 96개의 64Kbps+168Kbps의 overhead

  DS-3 : 44,376Mbps, 672개의 64Kbps+1.368Mbps의

               overhead

  DS-4 : 274,176Mbps,4032개의 64Kbps+16.128Mbps의

               overhead


  Kyung Hee
  University
                                                     46
               Multiplexing application(cont’d)
T Lines


 Service         Line   Rate(Mbps)     Voice Channels

 DS-1            T-1        1,544            24
 DS-2            T-2        6,312            96
 DS-3            T-3       44,736           672
 DS-4            T-4      274,176          4032


  Kyung Hee
  University
                                                        47
               Multiplexing application(cont’d)
T lines for Analog Transmission




  Kyung Hee
  University
                                                  48
                 Multiplexing application(cont’d)
T-1 frame structure




    Kyung Hee
    University
                                                    49
               Multiplexing application(cont’d)
Fractional T Lines




                   DSU/CSU (Data Service Unit / Channel Service Unit)
  Kyung Hee
  University
                                                                        50
               Multiplexing application(cont’d)
E Lines
  Europeans use a version of T lines called E lines



  Service            Rate(Mbps)        Voice Channels

     E-1                 2,048                  30
     E-2                 8,448                 120
     E-3                34,368                 480
     E-4               139,264                1920

  Kyung Hee
  University
                                                        51
               Multiplexing application(cont’d)
Other Multiplexing Service


  ISDN(Integrated Services Digital Network)


  SONET(Synchronous Optical Network)


  ATM(Asynchronous Transfer Mode)




  Kyung Hee
  University
                                                  52
                8.6 Digital Subscriber Line (DSL)
 us 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




   Kyung Hee
   University
                                                             53
                            DSL (cont’d)
 Modulation Techniques
   CAP (carrierless amplitude/phase)
          similar to QAM
          carrier signal is eliminated
   DMT (discrete multitone technique)
          combines QAM and FDM
          the available bandwidth for each direction is divided into
           4Khz channels, each having its own carrier frequency




  Kyung Hee
  University
                                                                        54
                    DSL (cont’d)
 The concept of DMT with N channels




  Kyung Hee
  University
                                       55
                       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
    The upstream channel usually occupies 25 channels
    (60kbps x 20 = 1.5 Mbps)
    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




   Kyung Hee
   University
                                                            56
                      DSL (cont’d)
 ADSL and the bit rates in each direction




   Kyung Hee
   University
                                             57
                          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
   Kyung Hee
   University
                                                                 58
                        DSL (cont’d)
 SDSL (symmetric digital subscriber line)
    is same as HDSL but uses one single twisted-pair cable t
    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
   Kyung Hee
   University
                                                                  59
                          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


   Kyung Hee
   University
                                                             60
                   FTTC (cont’d)
 FTTC in the telephone network




  Kyung Hee
  University
                                   61
                   FTTC (cont’d)
 FTTC in the cable TV network




  Kyung Hee
  University
                                   62

				
DOCUMENT INFO