Data Transmission

Data transmission is a means of transmitting digital or analogue 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 analogue 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 bitstreams.  These data streams are positioned over a communication medium for transmission to the destination device.  An outward signal can either be a baseband or a 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

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

Further Readings:

• Data communication