MULTIPLEXING

MULTIPLEXING

1. Frequency-Division Multiplexing (FDM)

   • An analog technique
   • can be applied when then Bandwidth of a link greater than the combined bandwidths of the signal to be transmitted
   • DEMUX uses a series of filters to decompose the multiplexed signal to its components
   • Guard Bands prevent signals from overlapping
     • Number of guarband = n - 1 n= number of channel
   • ANALOG HIERARCHY
     • use to maximize the effeciency
     • Eg : AT & T system
       • group -> super group -> master group ->jumbo group
   • APPLICATION
     • Cable television
     • AM
     • FM

2. Wavelength- Division Multiplexing (WDM)

   • designed to use high data rate capability of fiber optic cable
   • concept same as FDM except thet the multiplexing and demultiplexing involve optical signals (lights) transmitted through fibre-optic channel
   • Light are multiplexed and demultiplexed by using a prism
   • DWDM
     • can multiple a very large number of channels by spacing channels closer to one another

3. TIME-DIVISION MULTIPLEXING (TDM)

   • digital technique
   • applied when data rate capacity of transmission medium is greater than the data rate required by sending and receiving devices
   • multiple transmissions can occupy a single link by subdividing them and interlaving the portions
   • SYNCHRONOUS TDM
     • MUX allocates exactly the same time slot to each device at all times
     • If a device unable to transmit or does not have data to send, its time slot remain empty
   • Frames ---->group of time slot ----->1 complete cycle of time slot
     • num. of time slot in each line = num. of input line
       • Framing Bits ----> one or more synchronization bits added to beginning of each frame ---->allows the DEMUX to synchronize the incoming stream ---->consists of one bit per frame, 0 and 1 alternately
         • Bit padding ---> MUX can add extra bits to a device's source stream to force the speed relationships among various devices into integer multiples of each other
     • Frame rate = Channel rate / Multiplexed bit
       • Frame duration = 1/Frame rate
         • bit rate = Frame rate x No. of bits in a frame
           • bit rate duration = 1/bit rate
   • EMPTY SLOT
   • DATA RATE MANAGEMENT
     • Multilevel Management
   • Digital Hierarchy
     • telephone company
       • through digital signal (DS) service
       • use T-line / E-line(european version)
   • Statistical TDM
     • to avoid the waste usage of the capacity of the line in synchronous TDM
     • allow lower speed input lines to be multiplexed to a single higher speed line
     • num. of time slot based on statiscal analysis of num. of input line

4. The set of techniques that allows the simultaneous transmission of multiple signal across a single data link

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