Wednesday, 14 March 2012

Data Transmission!!!

hai guys!!! I'm back...

          So, this time i want to talk about data transmission. Do you know how your data is transferred? the truth is when we talk about data transmission, it's all about speed and also size which mean how fast (time taken) for the data is transferred and also the size of the data that is transferred. But before going deep into this topic,first  I want to explain to all of that data travel in various characteristics (1.analog vs digital, 2.bandwidth, 3.serial vs parallel, 4.transmission timing, 5.transmission directions, 6.circuit switched, pocket-switch and broadcast connections, compression) :


  • analog signal is formed by continuously varying voltage levels that create a wave that can be gasped by an analog transmitter like microphone.
  • digital signal is the transmission of binary electrical that only have two possible states, 0 and 1 ( on and off). this can be called the language of computers.

  • bandwidth is the amount of data that can be transferred in a period of time or we can say that bandwidth is the maximum speed at which a particular communications medium can transfer the information.
  • medium with higher bandwidth deliver data faster.

  • For serial transmission, data is sent one bit at a time, one after another along a single path.
  • In serial transmission, when bits are sent sequentially on the same channel (wire), it will not only reduce the costs for wire but in the other hand, it will also slows the speed of the transmission.
  • Also, for this transmission, some overhead time is needed since bits must be assembled and sent as a unit and then disassembled at the receiver.
  • We usually use this type of communication for short communication for example between computer and printer.
  • In parallel transmission, multiple bits (usually 8 bits or a byte/character) are sent simultaneously on different channels-usually each bit in the byte taking separate path.
  • As a result, there is a speedup in parallel transmission bit rate over serial transmission bit rate. 
  • However, this speedup is a trade off versus cost since multiple wires cost more than a single wire, and as a parallel cable gets longer, the synchronisation timing between multiple channels becomes more sensitive to distance.
  • This transmission usually used between computer component e.g. buses

The next one is the transmission timing. Transmission timing is a very important aspect that we need to consider when the transmission of data happened. There are three types of transmission timing. They are synchronous, asynchronous and also isochronous transmission. Each of them did their work differently

a) synchronous transmission
  • the term synchronous is used to described a large group of data is transmitted in blocks.
  • this type of connection is used when large amounts of data must be transferred very quickly from one             location to the other.
  • in this method, both the ending device and the receiving device are operated simultaneously and are resynchronized after a few thousand data signal bits are transmitted.
b) asynchronous transmission
  •  Meanwhile, asynchronous transmission is the process where transmitted data is encoded with the start and stop bits, specifying the beginning and the end of each character and also the data sent is without being synchronized

c) isochronous  transmission

  • In isochronous transmission, the data is sent at the same time as other related data to support certain types of real time application. 
  • For example nowadays, we have streaming video and also music.


This means that during communication between two pieces of equipment, the process of exchanging data can be done in either three operation styles. The message source will be called transmitter while the destination where the message will be sent is called receiver to provide easier understanding on how the data flow actually work.

  • Simplex
- the data or information is transmitted in one direction only
- the role of transmitter and the receiver are fixed
e.g.  the radio station is a simple channel because it always transmits the signal to its listeners and   never allows transmitting back.
  • Half-duplex
- message can flow in 2 directions, but never at the same time.
- one station transmits information to another station without any interruption.
- the other station wills response after that transmission is completed.
- compared to the first style, both stations can now exchange its role between transmitter and receiver modes after each transmission.
e.g.  Walkie-talkie is one of the communication tools that use this type of exchange data style.
  • Full-duplex
- both station can transmit and receive simultaneously
- it really consists of 2 simplex channels
- one channel used to forward while another one as the reverse channel, linking at the same point.


1. Circuit switched - data used dedicated path from sender to receiver
2. Packet-switched - data sent as individual packets, which are assembled at the recipient’s  destination
3. Broadcast connections - data broadcast to all nodes within range

Data Compression

- Data compression encoding information using fewer bits than the original representation
- E.g. when you want to transfer your picture into the phone the data compressor will compress the  data about the picture to maintain the optimal resolution of the picture after the transfer.
- Compression is used just about everywhere. All the images you get on the web are compressed, typically in the JPEG or GIF formats, most modems use compression, HDTV will be compressed using MPEG2, and several file systems automatically compress files when stored, and the rest of us do it by hand
- Data compression is particularly useful in communications because it enables devices to transmit or store the same amount of data in fewer bits.

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