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Whether wired or wireless, most devices need to communicate with each other to be helpful. Even on a micro level, the device would lose functionality without communication between the components that make up a device. This is where data transmission comes in. Britannica defines data transmission as, “…sending and receiving data via cables (e.g., telephone lines or fibre optics) or wireless systems.”

Basically, data transmission is the process of sending data between two or more digital devices, either in analogue or digital format. It is the process that allows devices or components inside devices to communicate with one another.

Types of Data Transmission

There are two ways to transmit data:

  • Serial Transmission
  • Parallel Transmission

Serial Transmission

In serial transmission, the sender sends the data bits one after another over a single channel. A transmission is structured based on the order in which the data bits are received. In this transmission, one bit is transferred at one clock pulse. Serial Transmission is a full duplex as the sender can send and receive the data. It is used. Generally, serial transmission is used for long distances.

There are two types of Serial Transmission:

  • Synchronous Transmission
  • Asynchronous Transmission

Synchronous Transmission

With synchronous transmission, data is sent in blocks or frames. This transmission is the full-duplex type. Between sender and receiver, synchronization is compulsory. Synchronous transmission doesn’t leave gaps between data. It is more efficient and reliable than asynchronous transmission to transfer a large amount of data. Synchronous transmission is fast. It is costly. Synchronous transmission occurs at a constant interval of time. During this transmission, users must wait for the server to respond once the transmission is complete. Synchronous transmission needs precisely synchronised clocks for the information of new bytes.

Some examples of synchronous transmission are:

  • Telephone Network
  • Video conferencing

Asynchronous Transmission

In asynchronous transmission, data is transmitted using bytes or characters. This transmission is the half-duplex type transmission. Data is transmitted with start bits and stop bits. It does not require synchronization. Asynchronous transmission is slow. It is economical. Time intervals during asynchronous transmissions are random, not constant. There is no need to wait for the server to respond after the transmission is complete. Asynchronous transmission does not need synchronised clocks as a parity bit is used in this transmission for information of new bytes.

Walkie-talkies and emails are some examples of Asynchronous transmission.

Parallel Transmission

In parallel transmission, multiple data bits are transmitted simultaneously over multiple channels. It is much faster to send data using this method as compared to serial transmission. In parallel transmissions, n bits, n wires or lines are used to transmit the data. Thus each bit has its own line. In Parallel Transmission, eight bits are transferred at one clock pulse. Generally, Parallel Transmission is used for short distances. The circuit used in Parallel Transmission is relatively complex & unreliable. Data is either delivered or received during parallel transmission, making it half-duplex.

Parallel transmissions make use of a 25-pin port with 17 signal lines and 8 ground connections. The signal lines are structured as follows:

  • 4 lines – initiate handshaking
  • 5 lines – communicate and notify errors
  • 8 lines – transfer data

Comparison Between Serial and Parallel Transmission

Basis for ComparisonSerial TransmissionParallel Transmission
DefinitionData flows bit by bitData flows 8 bits (1 byte) at a time
Number of bits transmitted per clock pulse1 bit8 bits
ApplicationsLong-distance communicationShort-distance communication


  • Simplex: Simplex is a data transmission mode in which data can only travel in one direction, resulting in unidirectional communication. This mode limits a transmitter to sending data only and not receiving it. A receiver, similarly, can only receive data and cannot transmit it.
  • Duplex: Duplex data transmission is a kind of data transfer in which data can travel in both directions simultaneously. i.e., it is bidirectional. It is a two-way communication system in which both stations can broadcast and receive data at the same time.
  • Half-duplex: Half-duplex or Semi-duplex data transmission method allows data to travel in both directions but only one at a time. In other words, each station may broadcast and receive data, but not simultaneously. When one device sends, the other device can only receive, and vice versa.
  • Handshaking: Handshaking refers to the automated process of negotiating the establishment of a communication link between entities. It takes place before the transmission of data or any other communication and after establishing a channel between the two organisations.

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