Data Transmission

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Data transmission is a means of transmitting digital or analog data over a communication medium to one or more devices.  It allows the transmission and communication of devices in different environments: point-to-point, point-to-multipoint, or multipoint-to-multipoint.

Data transmission can either be analog or digital, but is mostly earmarked for sending and receiving digital data.  As such, data transmission is also referred to as digital transmission or digital communications.

It works when a device aims to transmit a data object or file to one or multiple recipient devices.  The digital data comes from the source device in the form of digital bit streams.  These data streams are positioned over a communication medium for transmission to the destination device.  An outward signal can either be baseband or passband.

Aside from external communication, data transmission may be done internally, between different parts of the same device.  The sending of data to a processor from the random access memory (RAM) or hard disk is a form of data transmission.

Types of Data Transmission

  • Parallel transmission – Several bits are transmitted together simultaneously within one clock pulse rate. It transmits quickly, as it utilises several input and output lines for sending the data.
  • Parallel transmission uses a 25-pin port with 17 signal lines and 8 ground lines.  The 17 signal lines are divided as follows:
    • 4 lines – initiate handshaking
    • 5 lines – communicate and notify errors
    • 8 lines – transfer data
  • Serial Transmission – Data is sent bit by bit from one computer to another in two directions.  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.  Data cables are used when transmitting data across a longer distance.  The data cable has D-shaped 9 pin cable that connects the data in series.

Comparison between Serial and Parallel Transmission

Basis for Comparison Serial Transmission Parallel Transmission
Definition Data flows in 2 directions, bit by bit Data flows in multiple directions, 8 bits (1 byte) at a time
Cost Economical Expensive
Number of bits transferred per clock pulse 1 bit 8 bits or 1 byte
Speed Slow Fast
Applications Used for long distance communication Used for short distance communication
Example Computer to computer Computer to printer

Types of Serial Transmission

There are two types of serial transmission – synchronous and asynchronous.  Both of these transmission methods use bit synchronisation.

Bit synchronisation is necessary to identify the beginning and end of the data transmission.

Bit synchronisation supports the receiving computer to recognise when data begins and ends during a transmission.  Therefore, bit synchronisation offers timing control.

  • Asynchronous Transmission – In asynchronous transmission data moves in a half-paired approach, 1 byte or 1 character at a time.  It sends the data in a constant current of bytes.  The size of a character transmitted is 8 bits, with a parity bit added at the beginning and at the end, making it a total of 10 bits.  It doesn’t need a clock for integration—rather, it utilises the parity bits to inform the receiver how to translate the data. It is straightforward, quick, and cost-effective, and it doesn’t require 2-way communication.
  • Synchronous Transmission – In synchronous transmission, data moves in a complete paired approach in the form of chunks or frames.  Synchronisation between the source and target is required so that the source knows where the new byte begins, since there are no spaces between the data. This method offers real-time communication between linked devices.

Synchronous and Asynchronous Transmission

Point of Comparison Synchronous Transmission Asynchronous Transmission
Definition Transmits data in the form of chunks or frames Transmits 1 byte or character at a time
Speed of Transmission Quick Slow
Cost Expensive Cost-effective
Time Interval Constant Random
Are there gaps between the data? Yes No
Examples Chat Rooms, Telephonic Conversations, Video Conferencing Email, Forums, Letters