Modes of Data Transfer

Modes of Data Transfer

Data Transfer along the communication media can take place in two ways: -

. Serial
. Parallel

Serial Data Transmission

If data is sent only bit at a time, then only one data line is required, along with the ground or signal return, as shown in Fig. 1.11. This is referred to as serial communications. Since information in the computer is usually stored and moved in parallel on the system buses, the data to be sent from a port to a device must be converted from parallel to serial. In Fig. 1.11, module A converts the parallel input data to serial form and sends it to module B in accordance with the clock input to module A.

Fig. 1.11 Serial Communications

Then why use serial communications? For distance longer than a few feet (room-to-room, building-to-building, etc.), the expenses and difficulty of installing groups of parallel wires increases greatly. Also, noise pickup and signal deterioration increases rapidly on transmission lines as distance increases. In order to reduce noise pickup, sometimes a separate ground wire is twisted together with each signal wire. Thus, in these cases, the number of wires will double and increase the cost even more for parallel transmission. Serial transmission is used to overcome these problems.

Serial data transmission is the one normally chosen for long-distance data communications, and most microcomputers have at least one serial data port, typically using an RS232 (serial) connector for data communication purpose.

This is in contrast to the parallel scheme where are number of bits are sent at the same time. The advantage of a serial scheme is that it only requires one wire for each communication channel, and one other wire for the current return path. Therefore a perfectly serviceable two-way communication scheme can be set up between say, a terminal and a computer, using only three wires.

Parallel Data Transmission

Data can be sent either one bit at a time or several bits at a time. When more than one bit of data is sent at a time, the data transfer is said to be in parallel.

Typically, parallel transfers are in a multiple of eight bits and require a data bus of eight or more lines as illustrated in Fig. 1.12. Recall that eight bits are sent for each data transfer under the control of the Send and Reply control signals.

Parallel data transmission involves simultaneous transmission of bits along several wires-usually nice. Parallel data transmission requires that bits be assembled at starting gates like race horses and simultaneously released down parallel wires when all bits are ready. Because nice wires are used to transmit messages, an entire character can be transmitted at once, rather than one bit at a time, and communications speeds are enhanced accordingly. This is one reason why many microcomputers use parallel data transmission for printers and the other peripheral equipment, typically using Centronics (Parallel) connectors.

Fig. 1.12 Parallel Data Transmission

Communication Systems

Communication Systems

In case of sending and receiving messages or data from one place to other place, we have many elements working together. All these elements put together to work efficiently is known as system. The communication system has the sole purpose of passing data or information in the most effective manner.

Communication system is the combination of the hardware, software and data transfer links that make up a communication facility of transferring data in a cost effective manner.

A communication system can either be analog or digital or a combination of the two. That is, the information can be transmitted in either analog or digital form with in the communication network. E.g. computer generated data are to be sent over analog telephone lines, the digital signals must be converted to analog form. The technique by which a digital signal is converted to its analog form is known as modulation. The reserve process that is conversion to its analog signal to its digital form at the destination device called demodulation. The process of modulation and demodulation that is the conversion of digital data to analog from and vice versa is carried out by a special device called modem (modulation/demodulation).

The analog form of message is sent via telephone line and then it reaches the destination where they are again transformed into digital pulses by the other modem connected with the receiver PC. Thus the message or data is transmitted and received by the two PC’s.

As the analog signal passes through the telephone lines, its strength starts decreasing with the distance, so amplifiers are used to boost the strength of the signal. These amplifiers add noise to the signal which sometimes causes disruption of the message. But good quality of the modem at receiving end as well as at the transmitting end is able to cut down the effect of the noise.

Data Communication & It's Components

Data Communication

Data Communication means sharing the information. This sharing can be local or remote or with in a building. Local communication usually occurs face to face, while remote communication take place over distance.

This term telecommunication includes telephony, television mean communication at a distance. The world tele is a Greek word which means “far”. The word data refers to the facts. In the context of computer information system, data are represented by binary information unit produced in the form of 0s (zero) and 1s (one).

Data Communication is the exchange of data between the two devices via some of transmission medium. Data communication devices must be the part of the communication system made up of a combination of Hardware and Software. The effective data communication has three fundamental characteristics.

1. Delivery. System must deliver the data to the correct destination.
2. Accuracy. System must deliver accurate data.
3. Timeliness. System must deliver the data in a timely manner.

Components of Data Communication

There are five major components of data communication system: -

1. Message. The information which is to be communicated.
2. Sender. Sending data communication device are the devices that sends data message. It can be computer, workstation, telephone, radio, camera and so on.
3. Receiver. Receiver is the device that receives the message. It can be a computer, workstation, telephone, TV and so on.
4. Medium. It is a physical path by which the message travels from sender to receiver.
5. Protocol. It is the set of rules that governs the data communication. It is agreement between the communication devices. Without a protocol, two devices may be connected but they are not communicating (With each other). Just as a person speaking Tamil cannot understand the language of the person who speaks only Punjabi.

Data Communication & Data Transmission Modes

Data Communication

In data communication, four basic terms are used i.e.

→ Data

→ Signal

→ Signaling

→ Transmission

Data refers to information that conveys or contains something of meaning to source/recipient. The information in data may be raw data or contain interpreted result from raw data.

Signal is the data encoding in the form of electric or electromagnetic waves to produce digital or analog signal.

Signaling is the process by which computer interacts with transmission media & sends the signal down the media.

Transmission is the communication of data achieved by propagation or processing of signals.

Data Transmission Modes

There are three ways as modes for transmitting data from one point to another. These are:-

→ Simplex

→ Half-Duplex

→ Full-Duplex

Simplex Mode of Transmission

In Simplex transmission, communication takes place only in one direction. Devices connected to such a circuit are either send-only or receive only device.

Fig-1.1 -- Simplex Mode of Data Transmission

Half-Duplex Mode of Transmission

A Half-Duplex system can transmit data in both directions, but only one direction at a time. This requires two wires. This is a common type of communication because one person can speak at a time. In this case line must be turned around each time the direction is reversed. This involves a switching circuit.

Fig-1.2 -- Half-Duplex Mode of Data Transmission

Full-Duplex Mode of Transmission

A Full-Duplex system allows information to flow simultaneously in both the direction on the transmission path. Use of Full-Duplex line improves efficiency because the line turn around time is removed. It requires four wires.

Fig-1.3 -- Full-Duplex Mode of Data Transmission