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Data Communications and Networks. What is Data Communications? Data communication is, in principle, the communication of information between computer systems. What is a Network?
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What is Data Communications? • Data communication is, in principle, the communication of information between computer systems. What is a Network? • A network consists of two or more computers that are linked in order to share resources (such as printers), exchange files, or allow electronic communications.
Types of Networks • LAN - Local Area Network • WAN- Wide Area Network • MAN- Metropolitan Area Network
A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN. • As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth. • A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN.
Metropolitan Area Network (MAN) is a computer networks usually spanning a campus or a city, which typically connect a few local area networks using high speed backbone technologies. A MAN often provides efficient connections to a wide area network (WAN). Example: If a company has a few offices in the same city, and the computer users at each location are able to share data between the two offices, they are generally doing this over a MAN.
Types of Transmission Media There are three major forms of transmission media used for LANs: Twisted pair: Two insulated copper wires twisted together in a regular spiral pattern; one pair establishes one communication link; it transmits electromagnetic signals. Twisted pairs are distinguished between shielded and unshielded twisted pairs according to their protection against electromagnetic fields. Unshielded twister pair (UTP) Shielded twister pair (UTP)
Coaxial cable: a single insulated inner wire is surrounded by a cylindrical conductor which is covered with a shield; it transmits electromagnetic signals. Coaxial cable is classified into two categories: baseband (uses digital signals) and broadband (uses analog signals) coaxial cable. Fiber Optic: consists of three concentric sections, the core (a fiber conducting optical rays), the cladding (reflecting optical rays) and the jacket (surrounding one or many fibers to protect them); transmits optical signals, which must be transformed to electromagnetic signals.
Wireless Media Types • There are several wireless media types including: • Radio • Microwave • Infared Micro waves travels at high frequency than radio waves and provide through put as a wireless network media. Micro wave transmission requires the sender to be inside of the receiver. Radio waves have the longest wavelengths in the electromagnetic spectrum. These waves can be longer than a football field or as short as a football. Radio waves do more than just bring music to your radio. They also carry signals for your television and cellular phones. Infrared frequencies are just below visible light. These high frequencies allow high sped data transmission. This technology is similar to the use of a remote control for a TV. Infrared transmission can be affected by objects obstructing sender or receiver.
These transmissions fall into two categories. • Point to Point: - Point to point infrared transmission signal directly between two systems. Many laptop system use point to pint transmission. These systems require direct alignment between many devices. • Broad Cast: - These infrared transmission use sprayed signal, one broad cast in all directions instead of direct beam. This help to reduce the problems of proper alignment and abstraction.
Wireless Network Technology Bluetoothis a specification for the use of low-power radio communications to wirelessly link phones, computers and other network devices over short distances. Wi-Fi, which stands for wireless fidelity, is a wireless networking technology used across the globe. In a Wi-Fi network, computers with wifi network cards connect wirelessly to a wireless router. The router is connected to the Internet by means of a modem, typically a cable or DSL modem. A hotspotis a site that offers Internet access over a wireless local area network through the use of a router connected to a link to an Internet service provider. Hotspots typically use Wi-Fi technology.
Modem (modulator-demodulator): A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. • Bandwidth: The term bandwidth has a number of technical meanings but since the popularization of the Internet, it has generally referred to the volume of information per unit of time that a transmission medium (like an Internet connection) can handle. • Broadband Internet access, often shortened to just broadband, is a high data rate Internet access. • Narrowband is a term used to describe an Internet connection speed that is most commonly associated with a dial-up connection. • Voiceband means the typical human hearing frequency range that is from 20 Hz to 20 kHz. In telephony, it means the frequency range normally transmitted by a telephone line, generally about 200–3600 Hz.
Communication Modes • 1. Simplex Mode:- In this mode of communication, only one way communication is possible. Example is radio and television broadcasting. In this mode there is just one communication channel. so, we can receive data on that channel but could not be able to transmit on same channel.2. Duplex:- Half-Duplex: In this mode of communication, two-way communication is possible but one at a time. If there is a location A and B so we can send data from A to B or from B to A but one at a time. Example is walkie-talkie or Push-to-Talk. In this mode there is also a single communication channel but it can be used in both direction for transmission.3.Full-Duplex: In this mode of communication, two-way communication is possible in both directions simultaneously . It means data can be sent from A to B and from B to A at same time. Example is Telephone/Mobile Communication. We can listen and talk at same time on telephone. In this mode there are two communication channels one for each direction of transmission.
Internet , Intranet and Extranet • The internet is the world wide collection of interconnected computer networks. It’s all the individual computers connected to those individual networks, plus all the users of those computers, all the information accessible to those users and all the knowledge those people possess. • Intranet is a private network within an organization or a department. • Intranets are the building blocks of extranets. If part of your intranet is available to people outside your organization such as customers and suppliers, the part you share with the outside world is an extranet.
Internet Concepts Email: electronic mail, the transmission of messages over communications networks. Newsgroup is an Internet-based discussion about a particular topic. These topics range from sports, cars, investing, teen problems, and some stuff you probably don't want to know about. Users post messages to a news server which then sends them to a bunch of other participating servers. Then other users can access the newsgroup and read the postings. Internet Relay Chat (IRC) is a system for chatting that involves a set of rules and conventions and client/server software. On the Web, certain sites such as Talk City or IRC networks such as the Undernet provide servers and help you download an IRC client to your PC. T
Telnet (teletype network): is a network protocol used on the Internet or local area networks to provide a bidirectional interactive communications facility. The Internet is a worldwide public network of computers on which people can join and use multiple services such as sharing of information. File Transfer Protocol (FTP), a standard Internet protocol, is the simplest way to exchange files between computers on the Internet. It's also commonly used to download programs and other files to your computer from other servers. Download: To copy data (usually an entire file) from a main source to a peripheral device. Downloading can also refer to copying a file from a network file server to a computer on the network. Upload: The opposite of download is upload, which means to copy a file from your own computer to another computer.
The term WWW refers to the World Wide Web or simply the Web. The World Wide Web consists of all the public Web sites connected to the Internet worldwide, including the client devices (such as computers and cell phones) that access Web content. Web browser, a software application used to locate and display Web pages. The two most popular browsers are Microsoft Internet Explorer and Firefox. Both of these are graphical browsers, which means that they can display graphics as well as text. HTTP (Hypertext Transfer Protocol) is the set of rules for transferring files (text, graphic images, sound, video, and other multimedia files) on the World Wide Web. As soon as a Web user opens their Web browser, the user is indirectly making use of HTTP. HyperText Markup Language (HTML)is a computer language used to create Web pages. HyperText is the method by which you move around on the web — by clicking on special text called hyperlinks which bring you to the next page. Markupis what HTML tags do to the text inside them.
XHTML is really the future of the internet. It is the newest generation of HTML. • XHTML stands for eXtensable HyperText Markup Language and is a cross between HTML and XML. XHTML was created for two main reasons: • To create a stricter standard for making web pages, reducing incompatibilities between browsers • To create a standard that can be used on a variety of different devices without changes.
URL A document on the World Wide Web. Every Web page is identified by a unique URL (Uniform Resource Locator). Website The term "website" represents a summary of all the content you have put online - each file takes part in what the website represents. Web server A computer that delivers (serves up) Web pages. Every Web server has an IP address and possibly a domain name. E-commerce (electronic commerce or EC) is the buying and selling of goods and services on the Internet, especially the World Wide Web.
e-learning • Education via the Internet, network, or standalone computer. e-learning is essentially the network-enabled transfer of skills and knowledge. e-learning refers to using electronic applications and processes to learn. e-learning applications and processes include Web-based learning, computer-based learning, virtual classrooms and digital collaboration. Content is delivered via the Internet, intranet/extranet, audio or video tape, satellite TV, and CD-ROM. Podcasting The practice of making audio files available online in a way that allows software to automatically detect new files and download them. Technically this is accomplished using RSS feeds to provide information about a collection of audio files in MP3 format. Podcasting lets anybody with a microphone; a computer and an Internet connection publish audio broadcasts that can be listened to by people anywhere in the world.
Bulletin board system (BBS) is a computer or an application dedicated to the sharing or exchange of messages or other files on a network. Originally an electronic version of the type of bulletin board found on the wall in many kitchens and work places, the BBS was used to post simple messages between users. VoIP (Voice over Internet Protocol) is simply the transmission of voice traffic over IP-based networks. The Internet Protocol (IP) was originally designed for data networking. The success of IP in becoming a world standard for data networking has led to its adaption to voice networking.
