Wednesday, 7 March 2012

second entry

Hi everyone :)

First of all I want to beg for forgiveness if my by blog is quite messy cause I'm still please forgive me....

Now, let's move on to the main topic. Yeahh!!! 

               these were basically what I have learnt in class........

  • Basically DATA COMMUNICATION is the collection and distribution of the electronic representation of informations FROM and TO remote facilities using electrical transmission system:- telephones lines, satellite or coaxial cable.
coaxial cable
  • The info can appear in any format:- data,text,voice etc…
                                 but most important!
                      RAW DATA must be DIGITIZED

  -Analogue signal
  -Digital signal                                                 
o   Like human voice 
o   Formed by continuously varying voltage level
                                                                                                       DIGITAL SIGNAL
  • the signals are converted into a binary code:- 0 & 1
Analogue to digital: modulation
Digital to analogue: demodulation
v         Hardware used to do the process: MODEM

  Unit of binary digits:-
               1 bit= a single digit, either 1 or 0            
               1 byte = 8 bits
               1 kilobytes=1024 Bytes
               1 megabytes=1024 Kilobytes
               1 gigabytes=1024 Megabytes
               1 terabytes=1024 gigabytes

1.      Parallel Transmission
-A group of bit is transmitted simultaneously by using a separate line for each bit 
2.      Serial Transmission
-Transmit all the bits one after another on a single line
-bit slower compared to parallel
-2 serial transmission modes
Ø  Synchronous Transmission
Ø  Asynchronous Transmission

Synchronous Transmission
o   A large group of data transmit in a block called a FRAME
Asynchronous Transmission
o   Bits divided into small groups(bytes) & send independently.
o   A bits can be send at any time & receiver never know when they will arrive.

- Simplex
2.      -Half-duplex
3.      -Full-duplex
  i.            SIMPLEX
        One direction of data transmit                             
·         Role of transmitter & receiver are FIXED          
·         Eg. Radio station, TV

ii.            HALF- DUPLEX
·         Message flow at 2 direction but NEVER at the same time
·         One station transmit into another without any interruption. The other station will response after that transmission has been completed
       Eg. Walkie-talkie                                                        

 iii.            FULL- DUPLEX
·         Can respond at the same time
·         Eg. Chatting, phonecall

fuhh!!! last but not the least is.......

·       =  Technique that enable more than 1 device to combine & send their signals simultaneously through a single      data link at the same time
·        = Different data uses different method to transfer
·        = Each link has a carrying capacity
·       =  Eg. Coaxial cable, optical tube

  i think that's all from me bye2......       

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