NETWORKING
Communication Networking
Communication is the process of transfer messages from one place to another. Data communication is the transfer of data or information from one location to another by means of communication channels. Communication involves 3 basic elements.
- Sending unit – Sender
- Transmission channel – medium
- Receiving unit – receiver
Communication channels
Telephone Line: - It consists of, which are made up of copper wire. Data transmission is up to 9600 bits/sec. Coaxial cable: Fiber Optic cable: Satellite
Microwave communication
Microwave communication uses high frequency radio wave that travels in straight line through the air. These signals can’t bend or pass through obstacles like heat and Rock Mountains. Hence the transmission and receiver are mounted on very high places especially on high towers. Microwave is a good medium for sending data between buildings in a city the waves are relayed by means of discs.
Internet Application
INTERNET
Internet can be defined as international network of computers. It can also define as network to networks. Internet was launched in 1969 when U.S. develops a project Advance Research Projects Agency Network (ARPANET).
Communication
Communication via E-Mail is the most popular Internet activity. You can send E-mail to your friend located anywhere in the world.
Shopping
You can purchase goods through Internet.
Entertainment
Movies, Listen music, read Magazines and so on using Internet.
Research
You can search for a particular topic.
Electronic mail is very powerful tool for electronic communication. Which enables to send message data electronically. An E-mail message has 3 basic elements- Header, Message and signature
The header part includes-
· Subject – A one-line description used to represent the topic of message.
· Addresses - It contains address of sender and receiver.
· Attachments – It allows you to attached file or document.
Message comes next. Finally the signature provides additional information about sender.
Address
The Internet uses an addressing method known as Domain name System “DNS”. This system divides an address into 3 parts
- Domain Code
- Domain Name
- User Name
The last part of the address is the domain code that identifies the organizational identification, separated from the Domain code by a dot (.) is the domain name. It is a reference to the particular organization separated from domain Name by an “@” symbol is the user name that identifies a unique person.
Domain Code Identification
COM Commercial
Edu Educational
Org Organization
Net Network
Gov Government
Browsers
The web is accepted through your computer using special software, known as browser. For retrieving data from Internet users required an interface that is called Browser. This software connects you to remote computer open and transfer file displayed text and images. Two well-known Browsers are Microsoft Internet Explorer and Netscape Navigator.
URL (Uniform resource Locator)
For browser to connect to other computers, the address is required these addresses are called uniform resource locator. URL is used to identify and locate websites, having 2 basic parts. First part represents the protocol and second part represents the domain names:
HTTP Hyper Text Transfer Protocol.
WWW World Wide Web.
TCP/IP (Transmission Control Protocol/Internet Protocol)
This part is used to break the data into small packets and IP part is used to address the packets that is protocol control, how message are broken down, send and reassembled.
Instant Messaging
Instant messaging allows or more people to communicate, that is life communication to use instant messaging you have to specify a list of friends, when you connect to internet it notifies you if any of your friend are on online. You can send and receive messages.
MODEM
Modem
Telephone lines typically send and receive analog signals. Computer sends and receives digital signals, to convert digital signal of computers to analog signals and vice versa modem is used. The word modem is a short form of modulation and demodulation. Modulation is the process of converting from digital to analog. Demodulation is the process of converting analog to digital. Communication speed is bits/sec. There are three types of modem.
External Modem
External modem stands apart from the computer and is connected by a cable to compute. Another cable connects modem to telephone wall jack.
Internal modem
Internal modem is inside the system unit, a cable is required to connect modem to telephone jack
Wireless modem
It is similar to external modem. Unlike an external modem it doesn’t connect to telephone wall jack rather wireless modem receives through air.
Client – Server – Node
Client
Client is a node that request and uses resources available from other node.
Server
Server is a node that shares resources with other nodes. Depending on the resources shared, it may be called a file server, printer server or data server.
Node
A node is any device that is connected to a network. It could be computer printer.
Network strategy
Every network has a strategy that a way of co-coordinating the sharing of information and resources.
Peer-To Peer Network System
In a Peer-To-Peer network system nodes can acts as both server and client. That is computer can obtain files located on another computer and can also provide files to other computers.
Client- Server Network System
In Client- Server Network System uses one computer to coordinate and supply services to other nodes on the network. The server provides access to centralize resources such as applications, software, hardware or database.
What is Internet?
The Internet is a great resource for everything from researching the latest cars on the market to paying bills, researching papers, and a myriad of other tasks that require gathering information. Over the net you can purchase concert tickets, order a computer, make airline and hotel reservations, compare prices, and perform many other errands, all from the comfort of your or office.
The Internet
The Internet is a worldwide network of computers that makes it possible to view and access information of all kinds. Computers on the Internet are connected to each other through cables, phone lines, satellites, and other connection devices. You can easily connect to Internet sites that are physically located on computers all around the world.
The World Wide Web
The web is a component of the Internet. Websites are pages of information that can include text, graphics, video, sounds, and animated images. Some websites contain only one page. Others, such as the library of congress site, contain hundreds of pages. You move from one page to another on the web by clicking hyperlinks. Hyperlinks are text or graphics on a page that open another page when he clicks on them, like turning the pages of a book. Some hyperlinks take you to another page within the current web site. Others lead to an A web browser is a program that you use to visit and navigate the web. Internet explorer is the web browser covered in this guide. A browser has commands for displaying and moving among web pages. It also allows you to create links to pages that you want to return to often. In Internet Explorer, these links are called favorites.
Web Pages Basic
Each web page has an address that specifies his location. A web browser uses this address to locate the page from all of the computers on the Internet. For more information on addresses, see Internet site addresses (URLs) in this guide.] Through web pages differ widely in design and format, most share some common features.
Internet Site Addresses (URLs):
All Web pages have an address that identifies the page and its location in the
Vast Internet network. A Web browser uses the address to locate the page.
An Internet address is also called a URL, which stands for uniform resource locator.
The address has several parts:
· The first part of the address is the protocol type. A protocol is a set of rules used to exchange information between computers. For example, the first part of a Web page address is http. This stands for Hypertext Transfer Protocol, the protocol used on the Web. The first of an FTP address is ftp, which stands for File Transfer Protocol. This type of the Internet site stores the files that users can download.
· After the protocol type, the address contains a colon and two forward slashes, such as http://
· Next the computer name identifies which computer (server) on the network contains the site. For example, www.aol.com, seattle.sidewalk.com, and www.microsoftcomputers.com all are computer names.
· The domain type is the three-character extension at the end of the computer name. It identifies what kind of organization administers the site. For example, .com (pronounced “dot com”) indicates a commercial or business organization, such as Microsoft.com. The .edu extension identifies an educational facility such as umich.edu, the University of Michigan site.
· An address can include a page name that identifies a specific page within a site. When you go from the home page (top level page of the site) to a page with the site, the page name is added to the end of the address; a forward slash separates the sites address from the page name. For example, the Seattle Sidewalk site home page address is http://seattle.sidewalk.com. If you go to the movie page within the site, the address for that page is http://seattle.sidewalk.com/movies.
· The web browser displays the address of the current page in the Address bar.
Show or Hide the Address Bar in the Explorer Window
1. In the Internet Explorer Window, click View, Tool bars, Address Bar. A check mark next to address bar indicates that the Address Bar is displayed.
2. To move the Address bar:
Place the mouse pointer over the “Address” title. Hold down the mouse button. The pointer changes to a four-headed arrow.
Drag the Address bar up or down to different toolbar or the menu bar.
3. To resize the address bar:
Place the mouse pointer over the bar at the left side of the Address bar. The
Mouse pointer changes to a double arrow.
Drag left or right to resize the Address bar.
Go to a Web Page by Typing URL
Click in the address bar text box. The current address becomes selected. Type URL you want to go to. Lick
Or
Data Transmission
Data transmission is the movement of information using some form of representation appropriate to the transmission medium. This will include:
§ Electrical signals carried along a conductor
§ Optical signals along an optical fiber
§ Electro-magnetic waves, e.g. Radio, or infrared signals transmitted through space.
Data Communications
Data communications includes data transmission, but also includes the control, checking and movement handling of information. In computer system, it includes:
§ The physical transmission circuits and networks
§ The hardware and software which support the data communication functions
§ Procedures for detecting and recovering from errors
§ Rules & protocols to ensure the disciplined (therefore comprehensible) exchange of information.
Methods of Data-Transmission
Communication Channel
The term Internal data transmission refers to the transfer of data within a computer, while external data transmission refers to the transfer of data to either local peripheral equipment (e.g. printers) or remote computers. A data communications channel is a path through a medium that data can take to accomplish a communications task. In effect, Channels are “data highways” caring signals from sending stations to receiving station along predefined routes. The communication links are established using
§ Paired wires and cables
§ Co-axial cables
§ Telephone lines
§ Microwave links
§ Fiber optic cables
§ Satellite links
The paired wires and cables
Computer joined by conventional wires are limited in their data rates and transmission distances. If there are many nodes on the network, this slow speed might not be acceptable. Faster methods have been developed using coaxial cable.
Co-axial Cable
Coaxial cable permits communications at much higher rate than conventional wires (even twisted pair wires) Because of its much better high-frequency transmission characteristics. In a coaxial cable, a conductive sleeve to form an electrical shield around the central wire surrounds a central wire, which carries the data signal. Coaxial cable is used in implementing a local area network called Ethernet. For longer distance and still higher speed data transfers, transmission media other than coaxial cable are used. These assure that the data arrive at their destination quickly and without error. In many cases, a terminal operator at a remote location, uses the regular dial-up telephone switching network, calls a number at the central processor location, and enters the data. For large volumes of data. However, it is often cheaper for an organization to acquire its own dedicated or leased line, which can be, used for both voice and data transmissions.
Satellite link
Beyond certain distance it is not possible to use communications through ground methods due to two main reasons, one due to fading of signals which can not be amplified without noise and second due to geographical reasons say sea, desert, mountains etc. In such cases, the data may be beamed to a communication satellite that acts as a reflector by accepting signals from one point on earth and returning the same signal to some other point on the earth. The satellite appears from earth to be a stationary target for the microwave signals because it’s precisely positioned 22,300 miles above the equator with an orbit speed that matches the earth’s rotation. Dozens of satellites are now in orbit to handle international and domestic data, voice, and video communications. Both the microwaves and lower-frequency radio waves can be used to create long-distance satellite transmission. At present, nearly 100 communications satellite are in stable “parking orbits” approximately 22,300 miles above the earth. Private companies, such as American Satellite Company, AT&T, COMSAT, operate these satellites, Intel sat, RCA, Satellite Business Systems, and Western Union that sell communications services to customers. The earth station operated by these private carries is located in major U.S. cities and project radio waves to the satellites. These signals are then reflected to yet other earth stations operated by these private carriers located in major U.S. cities and project radio waves to the satellites. These signals are then reflected to yet other earth stations for distribution to computer users. Like microwaves, satellite transmission based on radio waves is a long distance, line-of-sight communications medium.
Fiber - Optics
Broadband channels are used when large data volumes must be transmitted at higher speeds. Existing broadband channels are expensive and are generally used only by large organizations. However, the rapidly maturing use of fiber-optic cables and laser technology allows huge amounts of data to be routinely transmitted at the speed of light through tiny threads of glass or plastic. Tamed with a laser, a single glass fiber of the size of a human hair can transmit across the country in a single second all the characters in dozens of books of the size of this book.
Data Transmission
Digital v/s Analog Transmission
Data is transmitted over communication channels in either analog or digital form. Analog transmission is used on traditional telephone lines: Messages are sent and received over telephone wires in the form of continuous electric waves that follow the path of the wire. Digital transmission, by contrast, carries data as distinct “on” and “off” states, just as the computer does. Analog transmission requires that data be converted from the digital form in which it is stored in the computer to analog form before transmission, in process called modulation. At the receiving end, data must then be demodulated-converted from waveform to digital form-before the data is entered into the computer. Both modulation and demodulation are accomplished by devices called modems, a term derived from the words modulation and demodulation. Digital transmission requires no data conversion, so it reduces the time required to send messages and creates fewer transmission errors than analog transmission.
Mode Of Transmission
Modems handle the transmission of data in one of the three basic Modes:
§ Simplex
§ Half Duplex
§ Full Duplex
In simplex mode, data is transmitted unidirectional i.e. one way in between two modes. Only one data path is required. In full duplex mode data is simultaneously sent in either direction. It needs two data paths but is more versatile. In half duplex mode, a single path is employed for sending and receiving data as in full duplex mode, but one direction operation is done at a time. 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.
Serial Data Transmission
Serial data transmission means the simultaneous transmission of bits one following the other, through a single wire or channel, 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-communications purpose.
Parallel Data Transmission
Parallel data transmission means the simultaneous transmission of bits along several wires – usually nine. Parallel data transmission requires that bits be assembled at starting gates like racehorses and simultaneously released down parallel wires when all bits are ready. Because nine 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 other peripheral equipment, typically using Censorings (parallel) connectors.
* Advantages and Disadvantages of Parallel data transmission over serial transmission
The biggest advantage of parallel data transmission is speed. Since data bits are transmitted simultaneously down parallel wires instead of sequentially down a single wire, parallel data transmission is nine times faster than serial data transmission.
Disadvantages of parallel data transmission
1. The difficulty of readying and simultaneously releasing nine bits at their starting gates.
2. The problem of assuring the concurrent arrival of all transmitted bits at there receiving gates for proper interpretation,
3. The cost of expensive cable instead of twisted-pair wires for connections to external devices, and
4. The fact the many public carriers do not provide parallel data transmission service.
Modems
The word modem is short form modulator – demodulator. ”Modulation is the name of the process of converting from digital to analog. Demodulation is the process of converting from analog to digital. The modem enables the digital microcomputers to communicate across analog telephone lines. Both voice communication and data communications can be carried over the same telephone lines.
Modes of Data Transmission
In asynchronous transmission, the method frequently used with microcomputers, data is sent and received one byte at a time. A synchronous transmission is often used for terminals with slow speeds. Its advantage is that the data can be transmitted whenever
Convenient for the sender. Its disadvantage is relatively slow rate of data transfer.
Synchronous transmission is used to transfer great quantities of information by sending several bytes or a block at a time. For the data transmission to occur, the sending ands receiving of the blocks of bytes must occur at carefully timed intervals. Thus, system requires synchronized clock. Its advantage is that data can be send very quickly. Its
Disadvantage is the cost of the required equipment
Data and Information
Definitions
Data:
Data is the name given to basic facts and entities such as names and numbers. Good examples of data are dates, costs, numbers of items sold, employee names, product names, addresses, tax codes, registration marks etc.
This term is used to describe basic facts about the activities of a system, may be a business house, production center or educational institution. Data are generally in the form of names and numbers, times, dates, weights, prices, costs, employee’s name, product’s name, names of books, schools, students, teachers, roll numbers, etc.
Information:
Information are data which have been converted or organized into a more useful or intelligible form for direct utilization of mankind, as information help human beings in their decision making process. Examples are: Time Table, Merit list, Headed] tables, printed documents, pay slips, receipts, reports etc.
Networks may also be citywide and even international, using both cables and air connections. Here let us distinguish among three types:
1) Local Area Networks
2) Metropolitan Area Networks
3) Wide Area Networks
Local Area Network:
Networks with computers and peripheral devices in close physical proximity--Within the same building, for instance—are called local area networks (LANs). Linked by cable—telephone, coaxial, or fiber-optic—LANs often Use a bus form of organization.
Metropolitan Area Networks:
The next step up from the LAN might be the MAN—the metropolitan area Network. These networks are used as linked between office buildings in a city Cellular phone systems expand the flexibility of MAN’s by allowing links to car Phones and portable phones.
Wide Area Networks:
Wide area networks (WANs) are countrywide and worldwide networks. Among Other kinds of channels, they use microwave relays and satellites to reach users over long distances--for example, from Los Angeles to Paris. Of course the widest of all WANs is the Internet, which span the entire globe. The primary difference between a LAN, MAN, and WAN is the geo-Graphical range. Each may have various combinations of hardware, such as Microcomputers, minicomputers, mainframes, and various peripheral devices.
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