Second Chapter Lesson-2: Data transmission method.

At the end of this lesson-

  • 1. You will be able to explain the concept of data transmission method.
  • 2. You will be able to classify the data transmission method. 

In data communication system the method used to establish link to different devices and bit synchronization with time for data transmission within is called data transmission method.

Types of data transmission method:

Based on number of wire connections data transmission methods are of two types. Such as:

  1. Parallel data Transmission
  2. Serial data Transmission

Parallel Data Transmission: In Parallel data transmission, multiple data bits are sent at the same time over multiple channels. Each channel carries one bit at the same time.

Parallel transmission is used when:

  • a large amount of data is being sent;
  • the data being sent is time-sensitive;
  • and the data needs to be sent quickly.

For example- Parallel transmission is used to send data in video streaming. Because video streaming requires the transmission of large volumes of data. The data being sent is also time-sensitive as slow data streams result in poor viewer experience.

Advantages and Disadvantages of Using Parallel Data Transmission:

The main advantages of parallel transmission over serial transmission are:

  • it is easier to program;
  • and data is sent faster.

Although parallel transmission can transfer data faster, it requires more transmission channels than serial transmission. that means expensive.


Serial Data Transmission: In Serial data transmission, data bits are sent one after another over a single channel. Each bit has a clock pulse rate.  Eight bits are transmitted at a time with a start and stop bit known as a parity bit, which is 0 and 1, respectively. It is viewed as a reliable data transmission method because a data bit is only sent if the previous data bit has already been received. It ensures that data integrity is maintained as it transmits the data bits in a specific order, one after another. In this way, data bits are received in-sync with one another.

Serial transmission is used when:

  1. Serial transmission is normally used for long-distance data transfer.
  2. It is also used in cases where the amount of data being sent is relatively small.

Comparison between Serial and Parallel Transmission

Basis for ComparisonSerial TransmissionParallel Transmission
DefinitionData flows in 2 directions, bit by bitData flows in multiple directions, 8 bits (1 byte) at a time
Number of bits transferred per clock pulse1 bit8 bits or 1 byte
ApplicationsUsed for long distance communicationUsed for short distance communication
ExampleComputer to computerComputer to printer

Types of Serial Transmission:

  • Asynchronous Transmission
  • Synchronous Transmission
  • Isochronous Transmission

These transmission methods use bit synchronisationBit synchronisation is necessary to identify the beginning and end of the data transmission. Bit synchronisation supports the receiving computer to recognize when data begins and ends during a transmission.  Therefore, bit synchronisation offers timing control.

Asynchronous Transmission: In this transmission method one byte data or a character is sent from one device to another with uneven time interval between two character transfer.

Whenever data is propagated it is sent at once. Thus no memory is required for storing data. Normally a start bit and a stop bit is added with the data and total 10 bit data is sent. Sometimes a parity bit is added before stop bit for error checking.

Data bits can be sent at any time. Stop bits and start bits are used between data bytes to synchronize the transmitter and receiver and to ensure that the data is transmitted correctly. The time between sending and receiving data bits is not constant, so gaps are used to provide time between transmissions. 


  • No synchronization is required between the transmitter and receiver devices. Sender can directly transmit data and the receiver can receive that data.
  • The sender does not require any primary storage device.
  • Cost is very low to implement this method.
  • It is convenient while transmitting a little amount of data.


  • Data transmission speed is very low.
  • Efficiency is comparatively less.


  • Computer to Printer
  • Card reader to computer
  • Computer to card reader
  • Keyboard to computer


Synchronous Transmission: In this transmission method data is sent block(chunks or frames) by block from one device to another with even time interval between two block transfer.

Data is stored in memory before sending to divide it into several blocks. Then it is transmitted block by block with regular interval. A block consist of several characters (Normally 128, 256, 512, 1024 characters) having header information (32 bit) at the beginning and trailer information (8 to 16 bit) at the end.


  • Efficiency is comparatively very high.
  • Speed of data transmission is very high.
  • No need to transmit start and stop bit.
  • In case of transmitting a lot of data, this method is suitable.


  • Primary storage device is required.
  • Comparatively expensive.
  • Synchronisation between the source and target is required.


  • Computer to Computer data transmission


Isochronous Transmission Isochronous transmission is similer to synchronous transmission but the time interval between blocks is almost zero.

In this transmission synchronous and asynchronous data is collected from several devices within a time slot (125 micro-second) and then passed those collected data as time frame through a synchronous data link one after another.


  • This method is used in real time application.


Synchronous VS Asynchronous Transmission:

Point of ComparisonSynchronous TransmissionAsynchronous Transmission
DefinitionTransmits data in the form of chunks or framesTransmits 1 byte or character at a time
Speed of TransmissionQuickSlow
Time IntervalConstantRandom
Are there gaps between the data?YesNo
ExamplesChat Rooms, Telephonic Conversations, Video ConferencingEmail, Forums, Letters

Lesson Evaluation-

Knowledge Based Questions:

  • a. What is data transmission?
  • a. What is parallel transmission?
  • a. What is serial transmission?
  • a. What is asynchronous transmission?
  • a. What is synchronous transmission?
  • a. What is isochronous transmission?

Comprehension Based Questions:

  • b. Explain Character by character data transmission method.
  • b. Why asynchronous transmission takes more time? explain.
  • b. Explain transmission method for transmitting data from keyboard to computer.
  • b. “It is possible to transmit data in even time interval”-explain.
  • b. Why is primary memory is required in synchronous method?-explain.
  • b. Explain the transmission method of facebook live.
  • b. Explain the transmission method of video call.
  • b. “It is possible to transmit data in the form of block/frame/packet”-explain.

Creative Questions:

Multiple Choice Questions:


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