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<p><strong>Scale of Computer Networks</strong></p>

<p>Conceivably, the most significant change in Computer Engineering and Science over the past twenty years has been the enormous growth of networks and their importance in the daily lives of billions of people. Because of this growth, and the diversity of networks now widespread across the globe. Computers may connect to each other by either wired or wireless media. &nbsp;There is no doubt that computer networks, also known as datacom or data transmission networks, represent a logical result of the evolution of two of the most vital scientific and technical of modern civilization called computer and telecommunication technologies.</p>

<p>A computer network consists of two or more computing devices that are connected in order to share the components of your network (its resources) and the information. Our working definition of a computer network is &ldquo;any system that allows communication between devices that perform algorithms on data.&rdquo; Although devices that perform data processing are now invariably digital systems, not all of the devices connected to networks are data processing devices. Examples are a microphone, an analog telephone and refrigerator. The history of networks, described below, includes many non-digital devices and, as networks become ever-present, more and more types of devices are connected to networks.</p>

<p>The historical and anthropological study of social networks, how humans interact and communicate, is not limited to communication by electricity,</p>

<p>radio, and optical systems. However, for our discussion it is more useful to begin with the electrical telegraph and telephone systems that became the foundation for what would become the first computer networks.</p>

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<p><strong>Telegraphy and Broadcasting</strong></p>

<p>The first telegraph systems had no mechanical repeating .Repeating is crucial because an electrical signal can only travel so long before it is too weak to be useful. Therefore longer distances, a person had to listen to the Morse code or other coded signal and repeat the message by entering it again, physically tapping it on a key. A repeater is solely a device that does the job of repeating a signal cleanly and clearly so that it can travel for longer distances without signal degradation. Telegraph lines with repeaters were really the beginning of networks, in recent time. Many types of repeater are still important to networks. There are similar limitations on wireless signals and signals transmitted through optical fiber so these networks also often use repeaters. After communication, systems became more than just one line with one transmitter and one receiver at a time, the next problem was how to get a message from one end to another on a network that had many possible destinations. One possibility is to have each message broadcast to all destinations at once over the whole network. Many networks still use this principle. Radio and television networks have operated on the same broadcast principles for over half a century, except for various changes in the format of information being sent and received (for example FM vs. AM, analog vs. digital, etc.).</p>

<p>One problem with broadcasting is that most systems could only take one message at a time per channel or per line .On such systems there must be away to avoid collisions , messages interfering with each other because of more than one sender using a single medium. Avoiding collisions is still an important task in modern communication networks.</p>

<p>The data transmitted by telegraph was essentially digital and in a binary form. This binary form was usually in a form not based on binary numbers but easy for human operators. Mechanization of the codes meant switching to regular-length codes based on binary numbers, such as the Baudot code. Developed by &Eacute;mile Baudot, this code was a five-bit binary code for sending (upper case) alphabetic characters, other characters, and control sequences. This code was later developed into the ASCII (American Standard Code for Information Interchange) which is used in many programming languages and other computer applications.</p>

<p><strong>Telephony</strong></p>

<p>Unlike telegraph, the telephone could transmit analog data. The developers of the telephone (like the developers of many networks) did not foresee its main purpose, for voice transmission .Suddenly special training was no longer necessary and smaller businesses, organizations, and homes could be part of the network. However, the increase in the number of possible receivers and the need to send to just one (or a small number) is a problem on an open network.</p>

<p>Point-to-point access requires some kind of switching . As with repeating, this job was originally done by human operators who listened for signals (voice or code) and physically connected the lines or turned switches. Automatic electromechanical switches were developed to take the place of human operators and automatic switching became such an essential change that we still call a telephone network a Public Switched Telephone Network or PSTN.</p>

<p>In many countries, public companies were given a monopoly over providing telephone services, in exchange for providing broad PSTN coverage.</p>

<p>Telephone monopolies at first resisted connection of unapproved devices, such as a modem (modulator-demodulator). As more computers connected, the global PSTN and its various networks became the foundation for many early computer networks and still has a major role in computer networks, both on a local and a global level.</p>

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<p><strong>The First Computer Networks</strong></p>

<p>Military research groups began to investigate the large-scale coordination of digital information in the 1950&rsquo;s. The Semi-Automatic Ground Environment</p>

<p>(SAGE) was a US Air Force project designed to bring together various military data, such as radar data. One developer of SAGE brought the networking ideas to business with the airline reservation system called the&nbsp; Semi-Automated Business Research Environment (SABRE). These and other advances resulted in a variety of different networks developing around the world, networks with completely different protocols .A protocol is a mutually understood method of transaction, without which meaningful communication</p>

<p>is impossible. The Internet as we know it today requires some way of uniting these various networks under shared protocols.</p>

<p>In the late 1960&rsquo;s, the Advanced Research Projects Agency Network, known as ARPANET, was formed from smaller networks. ARPANET was a military project but, at a very early stage, it began to connect many non-military organizations, including educational institutions. Under this project, the first large-scale integration of networks was attempted. It was called &ldquo;internetworking&rdquo; but this adjective was shortened to internet . Eventually the word became a proper noun and the National Science Foundation (NSF) took over the growing Internet , as NSFNET. By this time, the expansion of Unix distributions, especially BSD Unix (Berkeley Software Distribution Unix), had allowed many universities to join the new global network.</p>

<p>Corporations had been involved as research partners but the network was still not open to specifically commercial uses. The NSF opened the Internet for commercial use in 1991. Whether we look at number of devices connected or the amount of traffic, the growth of the Internet has been exponential in this century. However, contribution of some methods to actualize the goal of computer networks cannot be over emphasized such as Batch processing and mulititerminal systems.</p>

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<p><strong>Batch processing Systems</strong></p>

<p>Batch processing played important role because of bulky and high cost of mainframe computers. These computers never handled the users interactively as expected leading to batching of jobs and later delivery of computation. This is called centralized system.</p>

<p>The need to allow users be in charge of managing data in an interactive mode became paramount, therefore more research on the technology.</p>

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<p><strong>Multi-terminal systems: Prototype of the Computer Network.</strong></p>

<p>In 1960s, a switch to new methods of organizing computer processing for efficiency evolved, these methods took into accounts the end users expediency thus multiterminal systems. Terminals moved out of computing centers onto desktops over entire organizations as at then. Nevertheless, processing power is solely centralized, some functions as data inputs and outputs became distributed due to high number of users. This highly looked similar to Local Area Networks (LANs) of today. Access to shared files and peripheral devices turned reality and maintained the illusion of using the computers in an exclusive mode by the users.</p>

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<p><strong>First Wide Area Networks (WANs)</strong></p>

<p>Wide Area Networks evolved first joining geographical distributed computers in countries.</p>

<p>The moment distributed systems appeared, not only were there connections between terminals and computers but also connections was implemented between computers. It all started with the solution of a simpler task by providing access to a computer from remote terminals located hundreds and thousands of kilometers apart.</p>

<p>Computers were able to interact in terms of data exchange on automatic mode, which is the basis for computer networking.</p>

<p>During process of Developing WANs, modern fundamental computer networking ideas such as th