MODEM(THEORITICAL EXPLANATION)

                                        MODEM        

WHAT IS THIS ?

                     The abbreviation of modem is MODULATOR - DEMODULATOR .It is an electronic device , generally to carry the information between   the two devices. It has two parts namely modulating part and demodulating part, the modulating part converts digital information (signals) into analog information (signals) and the demodulator does the reverse of modulator .


HOW THE CONNECTION IS ESTABLISHED?

     1 The sender (DTE) activate the modem (DCE) by sending some signals(RTS)

t                        DTE ------------> RTS------------> DC      2 The  modem(DCE) at the sending end send some signals (DCD)to the modem at the receiving             end(DCE)

         

                       DCE------------->DCD------------>DCE     

        series of signal is  transmitted between the  two modems , until the connection is established and         this process is termed as HANDSHAKING
      
    3  The modem at the receiving (DCE) end sends signal (DSR)to the destiny(DTE)

                          DCE-------------->DSR------------>DTE

    4 At last the the receiver(DTE) send the signal(DTR) back to the modem (DCE)from that it goes to another modem(DCE) and then it(CTS) is directed to the sender(DTE).

                { DTE---->DTR------>DCE } --------------> {DCE------->CTS------>DTE}   

                     RECEIVING END                                           SENDING END
    
          Finally the connection is established in this manner . So that the two devices are ready to                     transfer there datum.
  
ABBREVIATION FOR THE TERMS INCLUDED

1. DTE- Data terminal equipment  (computer)
2. RTS- Ready to send (signal)
3. DCE- Data communication equipment(modem)
4. DSR- Data set ready(signal)
5. DTR- Data terminal ready(signal)
6. CTS- Clear to send( signal)


HOW THE DATA IS TRANSMITTED?

    First we need to understand 
      
              WHAT IS ANALOG  AND DIGITAL SIGNAL ?
    
ANALOG SIGNAL: Signals which are continuous in nature .Since we are surrounded by the analog                                      signals. Example audio ,video , analog clock ,even voice of a human also                                              analog .  THE WAVE FORM IS SINE .


DIGITAL SIGNAL: They are discreet time signals . It is simply 0s and 1s . Example                                                             computer and all digital electronics .THE WAVEFORM IS LIKE SQUARE .
                                  Since it has two values alone mostly that too 5 (means high voltage/on) and                                           0(means ground/off)
  

                  MODULATION:

                        Process of converting digital to analog  signal . There are so many  Techniques are                                available. 
                   1. amplitude shift keying(ask)
                   2. frequency shift keying(fsk)
                   3. phase shift keying(psk)
                   4. differential phase shift keying(dpsk).


using any of the techniques the digital signal from the computer can be converted to the analog signal.The group digital binary data have certain range frequency .So the analog equivalence of digital data is just a superimpose of group of frequency, for to send a massive file we need to superimpose more frequencies ,but it is limited to certain range in a particular bandwidth.

                     
                
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