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Internet tybcom

  1. 1. DATA COMMUNICATION The transfer of data from one machine to another machine such that the sender and receiver both interpret the data correctly is called data communication. Data communication is concerned with the transmission of digital data. This transfer of data is in the form of bits 0 and 1. Some form of transmission medium is necessary for this exchange of data. Components of Data Communication System: A data communication system is made up of five components. These are: 1. Message: The message is in the information or data to be communicated. A message may consist of text, picture, audio, video or a combination of these. 2. Sender: The device that sends the message is called the sender. This may be a computer, a video camera, a Web camera, or a telephone instrument. 3. Medium: The physical path through which a message travels from the sender to the receiver is called the medium. E.g., coaxial cable wire, twisted pair wire, fiber-optic cable, radio waves, etc. The word “channel” is also used to refer to the medium between the sender and the receiver. 4. Receiver: The device that receives the message is called the receiver. This can be a computer, a television or radio set, or a mobile (telephone) instrument. 5. Protocol: A protocol is a set of rules that control the process of data communication. When two or more devices exchange data, there must be agreements on how this exchange will take place. E.g., at what speed will the sender transmit data, in which language, what if errors take place during the process o data transmission, and how these errors take place during the process of data transmission, and how these errors will be corrected, how to know that all the data has been transmitted. All these issues are handled by a set of rules called the protocol. Distributed Processing:
  2. 2. Distributed processing means that processing will occur on more than one processor. These multiple computers communicate with each other through a computer network. In distributed processing, a task is divided among many computers. Thus, a single computer is not responsible for all the processing, but each separate computer handles a part of processing job. Applications of Distributed Processing: 1. Internet, World Wide Web 2. Scientific computing, including grid computing 3. Real-time process control, e.g., nuclear power plant control system, aircraft control system 4. Banking system 5. Airline and railway ticket reservation system 6. Telecommunications, cellular networks Advantages of Distributed Processing: 1. Distributed database: One computer system cannot have the capacity to store all the data of an organization. In such a case, the database is distributed among multiple computer systems. 2. Security: The system can be designed so that a user can perform a limited set of operations and on a small set of the database. E.g., a bank may allow access to its database through an automated teller machine (ATM) but these transactions are limited only to the user‟s account, and not on the entire database. 3. Faster problem solving: When many computers are working at the same time on different parts of a problem, the problem can be solved faster than by a single machine working alone. Typical applications are breaking encryption codes, complicated scientific calculations, weather forecasting, etc. 4. Collaborative processing: Multiple computers and multiple users may interact on a single task. 5. Security through redundancy: Multiple computers running the same program at the same time provide security through redundancy. If one computer fails, the other can carry on the job.
  3. 3. NETWORKING Definition: A computer network is an interconnection of two or more computers such that they can share resources and information. These computers can be linked together using a wide variety of cables, telephone lines, or through satellites. The computers in a network communicate with each other using a set of rules known as PROTOCOL. Types of computer networks: All computer networks can be classified into three categories based on the following factors: a) Size (number of computers) of the network, b) Geographical range of the network i.e., the distance it covers, c) Ownership i.e., owned by a single organization, a public body like the municipal corporation, a national organization like the Indian Railway or airlines, or a global organization. The 3 types of computer networks are: Local Area Network (LAN), Metropolitan Area Network (MAN) and Wide Area Network (WAN). Local Area Network (LAN): A local area network is a network of computers in a limited geographical region, e.g., within a room or a building. It is an interconnection of many workstations and a file server through a central connecting device called a hub.
  4. 4. Metropolitan Area Network (MAN): A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. The latter usage is also sometimes referred to as a campus network. Wide Area Network (WAN): A WAN covers large geographic area with various communication facilities such as long distance telephone services, satellite transmission, and under-sea cables. The WAN typically involves best computers, network and much different type of communication hardware and software. E.g. Interstate banking networks and Airline reservation systems. WAN typically operate at lower link speeds (about 1 mbps). Network Structures: The way in which individual computers (called nodes) on a network interact with each other computers depends on how they are organized. The two basic types of network structures (or architectures) are: server-based (client-server model), and peer-to-peer network. 1. Client-Server model (Server-based): In this type of network, certain computers called servers are dedicated to provide various services to the other computers, called clients. The client and server are connected through a central hub.
  5. 5. 2. Peer-to-Peer Network: In a peer-to-peer network (also called P2P network), there are no dedicated servers. No single computer is assigned the role of providing services to all other computers. Each machine works as both a server as well as a client. The word “peer” means “equal”, and therefore in this type of network, all computers are equal Network Topologies: The geometrical arrangement of computer resources, remote devices, and communication facilities is known as network topology. A computer network is comprised of nodes and links. A node is the end point of any branch in the computer, a terminal device; workstation etc. a link is a communication path between two nodes. There are 4 main topologies which are discussed below: 1. Star Topology: This is the most common arrangement of computer systems and links between them. All devices are connected to central hub. The function of the hub is to deliver the data to and from the computers. The hub may be a server computer 2. Bus Topology: This topology is very popular with local networks. A single cable runs in the building and all nodes are linked along with this communication line. This cable is called the bus or backbone. The two ends of the cable are terminated with
  6. 6. terminators. We can imagine a bus picking up various people from one bus stop and dropping off people as it travels, and then picking up a few more. 3. Ring Topology: Ring topology is also used for local area networks. In this arrangement, a network cable passes from one node to another until all odes are connected in the form of a ring or loop. There is a direct point-to-point link between neighboring nodes. 4. Mesh Topology: In this, there is network random connection of nodes using communication links. This network lines are planned carefully after serious thoughts to minimize cost. Medias Network media refers to the medium used in computer networks for transmission of data. It is the actual path over which an electrical signal travels as it moves from one computer/device to another. This data transmission can take place either through wired media or wireless. There are 2 basic categories of Transmission Media: 1. Guided and 2. Unguided. A. Guided : Guided Transmission Media uses a "cabling" system that guides the data signals along a specific path. The data signals are bound by the "cabling" system. Guided Media is also known as Bound Media. Cabling is meant in a generic sense in the previous sentences and is not meant to be interpreted as copper wire cabling only. B. Unguided: Unguided Transmission Media consists of a means for the data signals to travel but nothing to guide them along a specific path. The data signals are not bound to a cabling media and as such are often called Unbound Media. Wireless Media: Wireless communication uses radio frequencies (RF) or infrared (IR) waves to transmit data between devices on a Local Area Network. In a wireless LAN, a major component is the wireless hub, or access point, used for signal distribution. Wireless Internet transfers digital data using radio frequency signals. Wireless connectivity is useful for business travelers who need access to Internet in cafes & airport. Network Protocols: Millions of computers of different types are connected on the Internet. Some of these computers may be running UNIX operating systems while others may be running under Windows operating systems. For all these computers to communicate with each other, they must speak a common language and follow some common rules.
  7. 7. The set of rules, which enables different types of computers to communicate with each other, is called protocol. The protocol used by the Internet for transferring messages from one computer to another is called the Transmission Control Protocol/Internet Protocol (TCP/IP). This term actually refers to two parts: Transmission Control Protocol (TCP): The job of the TCP is to break down every piece of data into small parts called packets. Each such packet also contains the address of the sender and the receiver. Internet Protocol: The job of the Internet Protocol (IP) is to find out how the data will go from point A to point B passing through a series of routers. These packets of data are sent over different paths until they reach their final destination. This is somewhat similar to the way regular mail passes through several post offices before it reaches its final destination. As the packets arrive at the destination, TCP takes over again, identifying each packet and checking to see if it is intact. Once it has received all the packets, TCP reassembles them into the original. TCP/IP (TRANSMISSION CONTROL PROTOCOL/INTERNET PROTOCOL): The protocol used on the internet is called TCP/IP. The TCP/IP has four layers: 1. The Application layer 2. The Transport layer 3. The Internet layer 4. The Network Interface layer OSI Model (OPEN SYSTEM INTERCONNECTION MODEL): This has been outline by international organization of standardization (ISO) to facilitate communication of software platforms each other. OSI MODEL is an abstract description for layered communication and computer network protocol design. The seven types of layers are as follows: 1. Application layer. 2. Presentation layer. 3. Session layer. 4. Transport layer. 5. Network layer. 6. Data Link layer. 7. Physical layer. INTERNET
  8. 8. Definition: The Internet is a worldwide collection of computer networks, co-operating with each other to exchange data using a common software standard. It can also be defined as “the global communications systems of diverse, INTER connected computer NET works for the exchange of information”. The Internet is also called as the Information Superhighway. Electronic Mail: E-mail is the short form of electronic mail. It can be defined as the exchange of messages and computer files between computers over a computer network. It is the method through which messages can be sent to other Internet users. It is the most frequently used component of the Internet. It has also been termed as the “killer app” of the Internet. Blogs: The word „blog‟ is a short form of the term weblog. It is a website, usually maintained by an individual. The various features of a blog can be summarized as follows: A blog is a personal diary, but put up on the Web so as to share information A weblog is a collection of text, images, and media files, arranged in reverse chronological order The activity of updating a blog is called “blogging” A person who keeps a blog is called a “blogger” Blogs are often written on a particular topic – e.g., photography, politics, entertainment, sports, etc Blogs are updated very frequently – often everyday As new entries are put up on a blog, the older entries are archived. These old entries are not available on the mail blog website but can be seen in the Archives section of the blog Comments: This is a special feature of a blog. Visitors to a blog can leave behind their comments on a form IP Addresses: The term IP stands for Internet Protocol. Each device connected to the Internet must be uniquely identified. This is similar to the telephone system where each subscriber has a unique telephone number. An IP address is a unique number assigned to every device that is on the Internet. A typical address may be look like this: This is called as DOTTED QUAD NOTATION. There are 4 parts (hence the word quad) of the address, separated by the dot (.) symbol. In each part, the number can vary from 0 to 255. There are no leading zeros in an IP address. Thus, the following is an invalid address: A mixture of decimal and binary notation is not allowed. So the following address in invalid: 11011000.27.61.137. IP address is unique. Each address defines one & only one connection on the internet. Two devices on the internet can never have the same address. But if a device has two connections to the internet, via two networks, it has two IP address. Domain Names: Every computer on the Internet has a unique IP address. But this numeric IP address is difficult to remember. Just imagine if you have to call all your friends by their mobile
  9. 9. numbers instead of their names! It would be impossible. The domain name is the computer name that can be used instead of an IP address. Domain names are easier to remember for human beings; e.g., it is easier to remember the address of Microsoft website as rather than IP address The Domain Name System (DNS was developed in 1984 by Dr. Paul Mockapetris) Domain Name System: DNS is the short form of Domain Name System. It is an Internet services that translates domain names into IP addresses. Because domain names are alphabetic, they‟re easy to remember. The Internet is however based on IP addresses. Uniform Resource Locator (URL): Each web page has a unique address called a Uniform Resource Locator (URL). Web address looks like this: Each URL consists of 3 parts: i. A PROTOCOL part ii. A HOST part iii. A DOCUMENT part http:// tells the Web browser that it is making a World Wide Web connection. http is the abbreviation of Hyper Text Transfer Protocol is the location of the web server, that is, the computer on which the web pages are stored Index.html is the filename of the web page that you are trying to access. Usually, this is the default page loaded by the browser when you enter a website. This is also called the home page. Search engines: Search engines allow users to find specific documents through keyword searches. If you have to search for, say information on monuments then just typing monuments will result in thousands of sites being listed that contain information about monuments. However, if you need information only about monuments in India, in South India, then entering the key words monuments, South India will result in more focused search. A search engine is a tool that searches for websites based on words that we give as search terms. Search engines look through their own databases of information in order to find what it is that you are looking for. Meta Search Engines: A Meta search engine is a search tool that doesn‟t create its own database of information, but instead searches those of other engines. “Metacrawler” and Dogpile, for instance search the databases of each of the other search engines such as Lycos, WebCrawler, Excite, AltaVista and Yahoo. Using multiple databases will mean that the search results are more comprehensive, but slower to obtain. The advantage of using a meta search engine is that the user does not have to type the same query separately in different search engines.