Computer Science 2210

Data Transmission


Data Transmission

Transmission of Data:

• It can be defined as the movement of data from one device to another in the form of bits.
• To transfer data, some form of medium is required e.g. fiber optics, etc.
• Data can be transferred over a short distance i.e. from computer to printer or over long distance i.e. overseas call via phones.
• Three major factors are required to be considered for the transfer of data:

1. Data transfer direction (one way or two way).
2. Transmission method i.e. no. of bits to be transmitted in one time.
3. Synchronization method.

Types of Data Transmission:

• There are two types of data transmission:

1. Serial
2. Parallel

Serial Data Transmission:

• In serial communication systems, there is a single wire over which data bits are transferred one by one.
• It is known as serial transmission because bits need to be organized before they are sent over the channel.
• This way the receiver can receive and arrange data in order and consider it to be errorless.

• This data transmission is best utilized when communication needs to be done over long distances.
• The data transmission speed in serial communication systems is slower compared to parallel communication systems.
• In serial data transmission, there is no issue of synchronization.


• An example of serial data transmission is the transfer of bits from the computer to the modem for transmission over the phone.

Parallel Data Transmission:

• In parallel communication systems, there are multiple lines of wires and data is transmitted simultaneously over these parallel wires.
• This data transmission method can be best utilized over short distances.
• If used over a long distance the synchronization issue can occur i.e. the bit can become skewed.
• It is used usually for internal communication in computer systems.
• It is faster as compared to serial data transmission.


• An example of parallel data transmission is ribbon wire that is used to transfer data from the computer to the printer.

Modes of Data Transmission:

• There are three modes of data transmission:

1. Simplex
2. Duplex
3. Half-Duplex

Simplex Data Transmission:

• In this mode, data is transmitted in one direction only i.e. sender to receiver.


• Transfer of data from computer to printer.

Duplex Data Transmission:

• In this mode, data is transmitted in both directions simultaneously.


• Broadband phone connection.

Half-Duplex Data Transmission:

• In this mode, data is transmitted in both directions but not simultaneously i.e. not at the same time.


• A phone conversation.

Error Detection & Correction in Data Transmission:

• In data transmission, during the transfer of data, noise and other impairments are introduced; the methods used for the detection of these is known as error detection.
• Error detection helps in data’s reliable delivery across channels.
• It also helps in reducing the undetected error probability i.e. the transfer of incorrect frames.
• Some kind of algorithm is applied before the transmission of data to produce an error-detection code that is usually sent over the channel with the data.
• The receiver applies the same algorithm and generates error code from the received data then compares it with the error code generated at the sender’s end.
• If both codes are the same then it means the data received is errorfree.
• Otherwise, the received data is considered incorrect and the receiver acts accordingly.

How Parity Bit Are Used For Error Detection:

• Data transfer also encounters noise and impairments that alter the digital signal.
• E.g. data sent 1001 can be received as 1101.
• To detect this type of error, the parity bit can be used.
• Parity bit system can be even or odd and it is the introduction of one additional bit at the start or end of the bitstream to transmitted.
• In even parity system, the number of occurrences of 1s needs to be even and decide whether parity bit should be 0 or 1.
• However, in an odd parity system, the number of occurrences of 1s need to be odd and decide the value of the parity bit.


Consider, the data to be transmitted in 1001001 and uses an odd parity system, so the parity bit will be 0 since the number of occurrences of 1s is already odd,

• Now suppose this data with the parity bit is transferred, and the receiver knows that the parity system used is odd.
• The received data block has encountered noise and altered to,

• In this case, the parity bit will help the receiver detect an error since it no longer corresponds to the odd number of occurrences of 1s. 
• The parity bit only helps in detecting 50% of the errors.
• However, in parity detection, there is a shortcoming that it cannot detect the error if more than 1 bit has been altered, e.g.

• In this case, no error will be detected.

Integrated Circuit (IC):

• In the initial time, data was sent in serial form i.e. one bit at a time over a single channel.
• With the advent of technology, Integrated Circuit (IC) introduced and allowed multiple devices on a single silicon chip.
• Because of it, the parallel transmission of data came into existence.
• Conventionally, it uses the transfer of a byte (8-bit) simultaneously making the transfer of data faster.
• The standard parallel interface uses a 36-wire heavy cable that was also expensive.
• Today, many ICs make use of serial and parallel data transmission.


• Multiplexer or ‘MUX’ is an example of an IC that utilizes both serial and parallel interface.
• It is a combinational logic circuit.
• It is used to switch multiple input signal lines to a single output line using a control signal.
• It works as a multiple position rotatory switch i.e. very fast.
• The input lines are also known as channels.
• It can be digital using logic gates or analogous using transistors, relays or MOSFET.

Universal Serial Bus (USB):

• It uses an asynchronous method for data transmission.
• It has been widely used today for the transfer of data from the computer to multiple devices.
• USB cable typically consists of four-wire shielded cable; two used for data transfer and the other two used for power and earth.
• USB is detected automatically by the computer system.
• The device is then recognized and the required driver is installed automatically.
• Around 127 devices can be connected to a single USB port using a USB hub.

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