Introduction

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Computer and Data Communications History Review

 

            People’s need for information elaboration pushed them, from the beginning of existence, to think and create many appliances which would help them to live a better life.

            Through years there were many researchers who thought of some automatic information-elaboration machines such as Pascal, Babbage and Hollerith.

In 20th century the first computer was built! It’s name was ENIAC and it was born in 1946. It was really huge. The year 1951 the first commercial computer hits ground and could process not only numbers but also characters. It was named UNIVAC I.             The computers of the first era which covers from 1942 to 1959 have for common logic element the lamps. These computers are huge, consume big amounts of electricity, they get really hot, they are slow and not so reliable.

Then there comes electronic revolution which opens new doors to the computer construction. The beginning of the 2^nd era of computers is a fact. It starts in 1959 and covers 5 years until 1964 where the lamps are replaced by transistors. The new computers are smaller, faster and their capacity is bigger than their predecessors. They also are more reliable and their price falls so they are within reach from many big organizations and universities.

            The 3^rd era of computers uses Integrated Circuits(IC) which contains transistors, capacitors and other components which have become very tiny. The use of integrated circuits makes computers smaller, faster, more reliable and bigger capacity. Their price falls too. The 3^rd era covers the time from 1965 to 1970.

The evolution continues and we reach our days were IC is still used as the basic component for building up computers. Nowadays though there are a lot more transistors in a single IC which is smaller than it used to be, faster and cheaper. For example, a simple silicon chip at the size of human nail contains hundreds of thousands of circuits. As a result of this reduction in size it’s the creation of the microprocessor(μP) and then the rise of microcomputers and super computers.

            Not long ago the word telecommunications implied voice communication. Today this term is used to address both voice and data communications. Networks are expanding to carry all forms of information such as voice, video, data and multimedia.

            We live at a time where technology changes rapidly. Technological innovations from 10 years ago are now finding their way into our daily lives. In 1960’s the Department of Defense in USA developed a military network capable of surviving attacks by routing the information around failed nodes and even be able to fix itself if necessary. The network was named ARPANET which later became the known to everyone Internet. They were using a protocol which is very popular today, the TCP/IP (Transmission Control Protocol/Internet Protocol).

            The data communication’s revolution had begun! By 1973 personal computers could easily stand in place for the main frame.  Personal computers were connected on the main frame as terminals. But there was a lack of communication of the computers with each other. In 1973 Xerox introduced to the computer world the Ethernet network. Robert Metcalfe developed the protocol which is in use today.

 

Essentials of Data Communications

 

For communication of any type to present there must be four basic elements present: a message, a sender, a receiver and a medium. The message should be understandable and there should be an ability to detect errors that may occur during data transmission. Let’s check them out:

The Message:

            Obviously when communicating, a message is needed. A message may vary in length and could be in several forms. For example if you want to run a program on a computer, you type its name or select its icon. When you do this you are communicating with the computer’s software by sending it a message to run the program. Data communications message types of messages include files, requests for services, response to requests, status messages, control messages and correspondence.

The sender:

            The sender is the transmitter of the message. It could be a person or an application or a machine with enough intelligence to originate a message or response without human intervention or a system user, sensor, badge reader or other input device.

The receiver:

            Bits being transmitted over a communication link are meaningless unless received by someone. Receivers include computers, terminals, remote printers or  people. There are three sender/receiver combinations: sender and receiver are in the same computer system, sender and receiver are in different computer systems which are directly connected and sender and receiver are in different computer systems that are connected via intervening computers systems.

            A node is a computer system connected to a network. Direct connections between two computers are called links. The connection between two nodes through an intervening node is called path. The determination of a message path is called routing and the method used to determine the route is called routing algorithm. In large networks the routing algorithm should have sufficient intelligence to choose the best path available.

The Medium:

            Messages are carried from sender to receiver through some communications medium such as wires, coaxial cables, fiber optic cables, radio waves and infrared light. Wires and cables carry electrical or light signals whether radio waves and infrared light are wireless media.

            We also have to consider understandability! In human language if two people are not speaking the same language it’s very difficult to understand each other and many times is impossible. The same goes for computers. Data may appear in a variety of formats. In order for the computers to communicate the data are send and received in some standard codes such as ASCII(American Standard Code for Information Interchange) and the EBCDIC(Extended Binary Coded Decimal Interchange Code).

            Error may occur in any kind of communication. In human communication we may detect errors easily which may be background noise, lack of concentration or ambiguous statement. People can correct misspelling, grammatical errors or even misstatements. It’s easy to retransmit a message. Computer networks lack of reasoning ability. For that reason they also transmit additional information along with the data to increase the chances of detecting errors. Error detection in networks occurs on several levels, such as node-to-node error checking across a link and end-to-end error checking over a path.

Networks

            A network is a set of devices connected by media links. A device may be a computer, a printer or any other device capable of sending and/or receiving data. The links connecting the devices are called communication channels.

            In electronic communication, there are two basic types of networks. The traditional network is a terminal network. This network consists of a single host computer with attached terminals. The host computer is called also server and does all or most processing whereas the terminals which are connected on it and they are usually referred to as client computers act as I/O devices through which a person gain access to server’s applications.

            The second type of network is a network of computers. This network consists of two or more computers connected by a data communications medium. The computers may have terminals connected on them. Usually the word ‘network’ refers to this type of network. There are many types of networks but they will be discussed in detail at a later stage.

Introduction to the Ethernet

            Ethernet is by far the most widely used LAN-connection technology today. Almost every LAN is built around Ethernet technology using components such as Network Interface Cards (NIC), repeater ports and switching hub ports.

Ethernet counts 30 years of history in 2003 and through all these years it has been reinvented many times in order to meet the need of speed and reliability.         

   The Ethernet was invented in May 22, 1973 by Bob Metcalfe of XEROX in California. He wrote a memo describing a network system he had invented for interconnecting computers so to make it possible to send data from one another and to laser printers.

All started from the Aloha network at the University of Hawaii where Norman Abramson and his colleagues developed a radio network for communication among the Hawaiian Islands. This was the early stage in the development of a common communications channel. The Aloha protocol went like this: An Aloha station could send whenever it liked and then waited for an acknowledgment. If there was no acknowledgment received in certain time the station assumed that another station had also transmitted simultaneously causing a collision so the receiver could not get a clear message. To eliminate collision both transmitting station choose a back-off time and then retransmit their packets.

            Metcalfe realized that he could improve Aloha network and he developed a system which actually detected collision. The system also included ‘listen before talk’, in which stations listened for activity (carrier sense) before transmitting and supported access to a shared channel by multiple stations. By putting all these components together we get the Ethernet protocol: Carrier Sense Multiple Access with Collision Detect (CSMA/CD). The first Ethernet system worked in late 1972 to interconnect the XEROX Alto at a speed of 2.94Mbps. Ethernet was born.

            Following the development of thin coaxial Ethernet came several new media varieties, including the twisted pair and fiber optic varieties for the 10Mbps system. Next, the 100Mbps Fast Ethernet system was developed which also included several varieties of twisted pair and fiber optic. Gigabit Ethernet systems was developed using both fiber optic and twisted pair cabling.

Other ways of transmission 

RS232

            In 1969 EIA (Electronic Industry Association) with Bell Laboratories established a recommended standard for interfacing terminals and data communication equipment. The objective of this standard was to simplify the interconnection of equipment manufactured by different firms. The standard defines electrical, mechanical and functional characteristics. Electrical characteristics include parameters such as voltage levels and cable impedance. The mechanical section describes the pin number assignments and plug. The connector itself is not specified. The functional description defines the functions of the different electrical signals to be used. RS232 stands for Recommended Standard number 232 set by EIA.

            In 1980’s industry found it cheaper to connect various peripherals using RS232 connection to their computers. Soon RS232 became the most common connection way between printers and microcomputers.

            The drawback of RS232 was the speed of data transfer because it only supported transfer rates up to 20kbps and soon industry discovered an other disadvantage: RS232 could only work up to 16m.

RS232

Parallel

            Parallel transmission is quicker than serial. The idea is simple: we use n wires to send n bits at one time. That means that each bit has its own wire and all bits are transmitted together with one clock pulse. Usually all wires are bundled together with a connection at each end. Parallel transmission is expensive but its n times quicker than serial. Because of its cost parallel transmission is limited to short distances. The most common application is the connection of printers to computers.