Digital Data Transmission

Digital data transmission is perhaps the breakthrough of the millenium. With the help of this technology, the communication and technology sectors have drastically improved.

 Data transmission is the process of sending digital or analog data over a communication medium to one or more computing, network, communication or electronic devices. It enables the transfer and communication of devices in a point-to-point, point-to-multipoint and multipoint-to-multipoint environment

 Binary data, consisting of 1s and 0s, may be organized into groups of n bits each. Computers produce and consume data in groups of bits such as we conceive of and use spoken language in the form of words rather than letters.

 A given transmission on a communication channel between two machines can be accomplished either in Parallel mode or Serial mode. Further, while there is only one way to send parallel data, there are two subclasses of serial transmission: Asynchronous and Synchronous.

 We shall discuss Serial and Parallel Transmission and Asynchronous and Synchronous Transmission in this article.

Serial versus Parallel Transmission: 

The transmission of binary data across a link can be accomplished either in Serial Mode or Parallel Mode.

Parallel Transmission

 In Parallel transmission, there are separate parallel paths corresponding to each bit of the byte so that all character bits are transmitted simultaneously.. Centronic port is the example of parallel port used for printer.

Serial Transmission

 In serial transmission, the bits of each byte are sent along a single path one after another. As one bit follows another, so only one communication channel is required between two communicating devices. RS-232 is an example of serial port used for the mouse or MODEM.

As in serial connections, wherein a single wire transports the data, the problem is how to synchronize the transmitter and receiver, in other words, the receiver can not necessarily distinguish the characters (or more generally the bit sequences) because the bits are sent one after the other.

 When a computer sends the data bits and parity bit down the same communication channel, the data are grouped together in predetermined bit patterns for the receiving devices to recognize when each byte (character) has been transmitted. There are two basic ways of transmitting serial binary data that addresses the problem of sequencing and re-arranging of data at receiver end: Asynchronous and Synchronous.

There are two types of transmission that address this problem:

Asynchronous Transmission

 In this, each character is sent at irregular intervals in time as in the case of characters entered at the keyboard in real time. So, the sender provides a synchronization signal to the receiver before starting the transfer of each message.

 For example, imagine that a single byte is transmitted during a long period of silence... the receiver will not be able to know if this is 00010000, 10000000 or 00000100. To correct this problem, each character is preceded by some information indicating the start of character transmission by start-of transmission information (called a START bit usually 0) and ends by sending end of- transmission information (called STOP bit usually 1)

Synchronous Transmission

 In this, the transmitter and receiver are paced by the same clock. The receiver continuously receives (even when no bits are transmitted) the information at the same rate the transmitter sends it. This is why the transmitter and receiver are paced at the same speed. In addition, supplementary information is inserted to guarantee that there are no errors during transmission.

 A group of synchronization bits must be placed at the beginning and ending of each block to maintain synchronization.

We shall discuss in detail about transmission mode in data transmission in the next article. Stay tuned for that.

 And like always, if you have any concerns, doubts or suggestions just click on ask questions at the left panel of your screen.

 Thank You.