Computer Network

electric pulses of varying amplitude. In digital technology, translation of information is into binary format (zero or one) where each bit is representative of two distinct amplitudes. Properties of Digital vs Analog signals Digital information has certain properties that distinguish it from analog communication methods. These include  Synchronizationdigital communication uses specific synchronization sequences for determining synchronization.  Languagedigital communications requires a language, which should be possess by both sender and receiver and should specify meaning of symbol sequences.  Errorsdisturbances in analog communication causes errors in actual intended communication but disturbances in digital communication does not cause errors enabling error free communication. Errors should be able to substitute, insert or delete symbols to be expressed.  Copyinganalog communication copies are quality wise not as good as their originals while due to error free digital communication, copies can be made indefinitely.  Granularityfor a continuously variable analog value to be represented in digital form there occur quantization error which is difference in actual analog value and digital representation and this property of digital communication is known as granularity. Differences in Usage in Equipment Many devices come with built in translation facilities from analog to digital. Microphones and speaker are perfect examples of analog devices. Analog technology is cheaper but there is a limitation of size of data that can be transmitted at a given time. Digital technology has revolutionized the way most of the equipment's work. Data is converted into binary code and then reassembled back into original form at reception point. Since these can be easily manipulated, it offers a wider range of options. Digital equipment is more expensive than analog equipment. Comparison of Analog vs Digital Quality Digital devices translate and reassemble data and in the process are more prone to loss of quality as compared to analog devices. Computer advancement has enabled use of error detection and error correction techniques to remove disturbances artificially from digital signals and improve quality. Differences in Applications Digital technology has been most efficient in cellular phone industry. Analog phones have become redundant even though sound clarity and quality was good. Analog technology comprises of natural signals like human speech. With digital technology, this human speech can be saved and stored in a computer. Thus, digital technology opens up the horizon for endless possible uses. Data Communication Terminology  Data Channel:-In this medium data carries from one point to another point.  Baud:-Each communication channel has certain capacity and it can carry information up to that extent only. This capacity measured in terms of Baud.  Bits per Second:-The speed at which data transferred between two points measured in terms of Bits per Second or bps.  bpsbits per second,  Bps-Bytes per second (Note capital B)  Bandwidth-The amount of data a communication system can transfer per unit time referred as Bandwidth of the system. Bandwidth simply indicates the data transfer rate. The more the data needed to be transmitted in the given unit time the more should be the bandwidth. Alternatively, it can be said that more the bandwidth of the communication system more will be the data transfer rate. Bandwidth measured in bps or Baud. Generally, a Baud is identical to bits per second. A rate of 100 Baud is equal to 100 bps.  In digital context, the level of bandwidth falls into three category:  Narrowband-Speed of narrowband varies between 45 to 300 Baud. Low speed devices use this narrowband channels.  Voice-band-Speed of voice-band channels ranges up to 9600 Baud. They are generally use in the ordinary telephone voice communication.  Broadband-The speed of broadband channels ranges up to 1 million Baud or more. High-speed devices use broadband for large volume of data transfer at high rate. Broadcast television, microwave and satellite uses broadband channel.  Data Transfer Rates:-The amount of data transferred per second by a communication channel is known as data transfer rate. It is measure in bits per second (bps). 1.3 Standard Organizations An association of organizations, governments, manufacturers and users form the standards organizations and are responsible for developing, coordinating and maintaining the standards .The purpose is that all data communications equipment are manufacturers and users comply with these standards. The primary standards organizations for data communication are:

When we communicate, we are sharing information. This sharing can be local or remote. Between individuals local communication usually occurs face to face, while remote communication takes place over distance. The term telecommunication means communication at a distance.

The successful transmission of data depends principally on two factors: the quality of the signal being transmitted and the characteristics of the transmission medium.

Chapter Two

Computers are used to generate information. Generated information is not useful in itself. The information must be delivered to the right person at the right time. Often information must be transmitted from one location to another. This process is called data communication. Here, we will be concerned with the hardware, software and procedures used in data communication.

2014

This subject is so vast that any attempt to address it within the limits of an introductory book has great chances to fail. A way to increase our chances of success is to reduce the subject to a few topics strictly linked to the instrumentation used in environmental sciences, and to the description of some examples of applications. In order to better understand this subject it is recommended that the reader be familiar with the way analog signals are converted into digital ones (Section (3.6)). All measuring systems produce data as a result, and these data must be evaluated sooner or later, either by an automatic system or a human being; "the final aim of a measurement process is taking a decision" (Ferrero, 2005). The immediacy with which the information should be assessed depends on the purpose for which it was collected. This purpose defines what to do with the information in the steps following the measurement: basically the information generated by an instrument can be stored, transmitted or both. The storage of information is treated at the end of the chapter, the transmission of data being the backbone of this chapter. It begins with a general introduction and goes on with generic issues on digital data with the purpose of establishing some concepts and the vocabulary frequently used. This generic approach to data communication concepts would hopefully help the reader to understand the transmission methods used at present in scientific instruments. Some characteristics of the transmissions systems, such as transmission delay, local and remote transmissions, network topologies, etc. are described. A concise mention of analog transmission is done followed by digital data transmission which, due to its importance, is the matter developed most extensively. Several digital transmission concepts, such as signal encoding, transmission modes, serial and parallel transmission, asynchronous and synchronous transmission, error detection and correction, etc., are developed with the aim of providing the minimum needed information to understand how instruments can transmit data. Finally, some effort is devoted to describe the three most commonly used media to transmit data from a field instrument (or group of instruments) to a central station, namely, private networks, digital telephony and satellite communications. It has to be stressed that in order to keep the explanations as simple as possible, the descriptions found in this chapter are basic. We do not delve into the details that some communications systems employ to transport data more safely. At present, complex communications systems employ very refined strategies and algorithms to protect the data and correct errors. These approaches, which increase transmitted data immunity and integrity, are merely delineated.

Data communication is the exchange of data (in the form of 1s and 0s) between two devices via some form of transmission medium (such as a wire cable). 2. What are the three criteria necessary for an effective and efficient network?