Networks and e-commerce notes

A computer network is a set of computers and devices joined so that they can share data, hardware and programs. The unit’s three types are named by span (how far they reach), not by “wired versus Wi-Fi” and not by the four computer sizes of Unit 1. A microcomputer in the lab can sit on a LAN and talk to a mainframe across a WAN; it stays a micro.

LAN (Local Area Network). A small area: one lab, one floor, one college campus building. High speed, low error, usually owned by one organisation. The B.A. English computer lab — a row of PCs, a printer, a switch — is a LAN. Sharing a printer and a folder of notes is the classroom job. Distance is metres to a few kilometres at most.

MAN (Metropolitan Area Network). A city or a large campus spread across a town. Bigger than a LAN, smaller than a WAN. Several college sites in Bikaner joined, or a city cable that many offices share, is MAN-scale. Speed is high; the owner may be a municipality or a service provider rather than one lab.

WAN (Wide Area Network). Large, even global. The Internet is the WAN everyone names. Railway reservation talking to a far server, a university result hosted in another city, a bank’s branches — WAN. Speed is often lower than a LAN; error handling and routing matter more because the path is long. A WAN is not merely a large LAN: it typically uses hired links (leased lines, ISDN, later public Internet) rather than cables the college itself laid inside one room.

Topology is the named shape of the links — how stations are wired (or logically arranged), not the brand of the PC. The books name bus, star, ring, mesh and usually tree.

Bus. One shared backbone cable. Every station taps it. Cheap and simple for a small lab of the older kind. If the backbone breaks, the whole bus is silent. Only one station should speak at a time or packets collide.

Star. Each station has its own cable to a central hub or switch. A lab PC going dead does not kill the others; the centre failing does. A hub repeats every incoming bit to every port; a switch forwards a frame only toward the destination port. A modern college lab is almost always a star around a switch. Easy to add a new PC.

Ring. Each station joins two neighbours in a loop. A token or a turn to speak travels the ring. A single break can stop the ring unless a second ring is built for backup.

Mesh. Many stations link to many others. Full mesh means every pair has a link — very reliable, very expensive, used where a WAN must not fail (backbone, some defence or bank cores). Partial mesh is fewer extra links.

Tree. Stars hung off a bus or off another star — a hierarchy, like floors of a college feeding a campus backbone. Hybrid in the books often means two topologies joined (star of labs on a campus bus).

These are the named boxes and links that join networks. A NIC (network interface) in the PC is the socket; these names are the equipment between networks.

A bridge joins two LAN segments that speak the same protocol (two Ethernet wings of one college). It forwards frames that belong on the other side and keeps local traffic local. It is not a modem and not a router: it works at the same kind of network, same language.

A router joins different networks and chooses a path. The Internet is a mesh of routers. A campus router decides whether a packet for the result server goes out on the college WAN link. It reads addresses and forwards; it does not merely repeat every bit to every cable.

A gateway joins networks that do not share the same protocol or the same way of naming — a translator at the door. An e-mail gateway between two mail systems is the classroom picture. All gateways route; not every router is a full gateway. Books treat gateway as the most “different-to-different” of the three (bridge / router / gateway).

A modem (modulator–demodulator) turns the computer’s digital bits into a wave a telephone line can carry, and back again. Dial-up Internet in older Rapidex pages is a modem on a phone line. It is both input and output (Unit 1). A modem does not choose Internet routes; a router does.

ISDN (Integrated Services Digital Network) is a digital telephone-network service that can carry voice and data on the same subscriber line, faster and cleaner than an analogue modem call. Books place it as a WAN access method: the college or office rents ISDN from the telecom.

A leased line is a dedicated circuit the organisation rents for exclusive, always-on use between two points — Bikaner campus to a city data centre, or a bank branch to the mainframe. You do not dial each time. Cost is for the line, not per call. WANs of railways and universities often sit on leased lines (and now also on public Internet).

Teleconferencing is a meeting held over a telecommunications link so that people in more than one place take part at the same time. Voice is the minimum: a phone bridge that joins Bikaner, Jaipur and a Delhi office. Documents can be shared as files or as a screen. It saves travel; it needs a reliable WAN or Internet link (last lessons) and agreed time.

Videoconferencing is teleconferencing with moving pictures as well as sound. Each site needs a camera (the webcam of Unit 1), a microphone, speakers or headphones, and software or a dedicated room codec. You see the speaker; you can show a slide of the Unit 1 diagram. Bandwidth is higher than voice-only: a weak college link makes the picture freeze while the voice still runs.

The difference the books want: teleconference = meeting at a distance, typically audio (and data); videoconference = that meeting plus live video. Both are applications of networks, not a fifth type of LAN/MAN/WAN. A class that hears a guest lecture from another campus without pictures is teleconferencing; the same class with a camera on the lecturer is videoconferencing.

E-commerce (electronic commerce) is buying and selling of goods and services using computers and networks — typically the Internet. A book ordered from a site, a railway e-ticket, a lab licence paid online are e-commerce. It is not “any use of a computer”: printing a notice in the lab is not commerce. The transaction is the point.

Benefits. The shop is open all hours. A student in Bikaner can buy from a seller in another city. Choice is wider; some prices fall because the shop-front is a server, not a rent on the market. Information (catalogue, tracking) is on screen. Growth came as PCs, Internet links, and cards became common, and as people trusted a purchase they could not touch. Limits sit beside growth: you cannot feel the cloth; delivery takes time; the link and the payment must be trusted (Unit 5 will name the crimes).

Categories the books name by who sells to whom. B2B (business to business): a publisher selling books to a college store. B2C (business to consumer): the same publisher’s site selling one Rapidex to Anil. C2C (consumer to consumer): a student selling a used textbook to another student on a listing site. C2B (consumer to business): a student offering a photograph or a small service to a firm. Some pages also name B2G (business to government) next to e-governance.

E-governance is government using IT to serve citizens, business and other government offices: information, forms, licences, results. Checking a university result on a website, filling an exam form online, a railway reservation against a government carrier — G2C (government to citizen) in the classroom. G2B is tenders and tax filing for firms; G2G is office to office. The aim is less queue, a recorded trail, the same rule for every roll number.

EDI (Electronic Data Interchange) is the computer-to-computer exchange of standard business documents — purchase order, invoice, despatch note — in an agreed format, without retyping on paper at each end. A book wholesaler and a college store can send orders as structured messages. EDI is older than a shopping website; it is a B2B link.

Electronic funds transfer (EFT) on EDI networks is the movement of money as a message on those same structured networks: the buyer’s bank is told to pay the seller’s bank when the EDI invoice matches. No bag of notes in a bus. EFT on EDI networks means the payment rides the business network, not only a person typing a password on a shopping page (that page is a later public form of the same idea).

An electronic payment system is any accepted way to pay without handing cash across a counter. Books name credit card (pay later, bank lends), debit card (pay now from the account), smart card (a chip that holds value or identity), electronic cheque, and e-cash / stored-value wallet. The OMR exam itself is not a payment; paying the exam fee online is.