Computer Networking, Internet & Online Services

Computer Network is a collection of distributed intelligent machines that are connected with each other with transmission media for the purpose of data sharing, communication and sharing of computer resources.

Advantages of Networking

There are considerable advantages of establishing a computer network for any organization. That is the reason of increasing popularity of computer networking.

• The following are the distinct notes in favor of computer networking.
• The computers, staff and information can be well managed
• A network provides the means to exchange data among the computers and to make programs and data available to people
• It permits the sharing of the resources of the machine
• Networking also provides the function of back-up.
• Networking provides a flexible networking environment. Employees can work at home by using office computer through networks.

Network Services

Network services are the thing that a network can do. There are 5 major network services that a computer network can offer – File Services, Print Services, Message Services, Application Services, and Database Services.

• File Services: This includes file transfer, storage, data migration, file update, synchronization and achieving.
• Printing Services: This service produces shared access to valuable printing devices.
• Message Services: This service facilitates email, voice mails and coordinate object oriented applications.
• Application Services: This services allows to centralize high profile applications to increase performance and scalability
• Database Services: This involves coordination of distributed data and replication.

There can be one or more computers providing these services for a network called servers. Network Server is a computer in Network that is designated to provide one or more network service. For example file server, database server etc. There are often a server providing more than one service but if there is a server computer that provides one and only one service, it is known as dedicated server.

A computer in network that connects to the server and uses the network services to perform user’s tasks is a client. If a computer network does not have any server computer (peer-to-peer networking) then each nodes are called workstations. A workstation is a node in network that is more powerful and can handle local information processing or graphics processing. A workstation usually has an inexpensive, small hard disk to carry out local tasks.

Some workstations that have no disk drive of their own is known as diskless-workstation or dumb terminals. They terminals completely rely on LAN for their access. Network operating system lets the node work as if all the resources at the server belong to the node itself.

Transmission Media

Each device connected to the network is generally known as a node. Each node is connected with cable or wireless technology known as transmission media. Transmission media is a pathway through which data are transmitted in network. We use different types of cables or waves to transmit data. There are two types of transmission media namely: bound transmission media (guided) and unbound transmission media (unguided).

Bound transmission media are the cables that are tangible or have physical existence and are limited by the physical geography. Popular bound transmission media in use are twisted pair cable, co-axial cable and fiber optical cable.

Unbound transmission media are the ways of transmitting data without using any cables. These media are not bounded by physical geography. Microwave, Radio wave, Infra red are some of popular unbound transmission media.

Bound Transmission Media

Twisted Pair Cable

A pair of wires twisted with each other is known as twisted pair cable. A set of four pairs of twisted wires are bundled to form cable. These are the most common medium for LAN. Wires are twisted with each other so as to reduce the interference.

We can find two types of twisted pair cables, namely: Unshielded Twisted Pair Cable (UTP) and Shielded Twisted Pair Cable (STP). The twisted pair cable that is protected against electro-magnetic interference (EMI) is known as STP and the one which is not shielded against EMI is called Unshielded Twisted Pair.

 

1–Jacket 2–Shield-braid 3–Shield-foil 4–Solid twisted pair 5–Drain wire

Co-axial cable

A solid central conductor surrounded by insulating material and then by a cylindrical shield woven from fine wires is known as co-axial cable. The shield is usually connected to electrical ground to reduce electrical interference. Co-axial cables have broader bandwidth and thus suitable for audio, video data transmission.

 

Fiber-Optics cable

A cable with central glass tube covered with protective shield which transmit data using photons is fiber optics cable. These cables transmit data via concentrated bursts of laser beams which are carried through bundles of hair thin glass fibers. They have advantages over electronic cables in transmission speed and volume. This technology has revolutionized telecommunication applications which used electronic cables. Fiber optic cable is free from electro-magnetic interference as well as wire tapping.

 

 

Comparison between BNC and UTP Cables

BNC	UTP
Derived from the thick Ethernet Coaxial Cable	Derived from telephone cable
Flexibility of adding nodes	Decided by Hub ports
Lower price and no need of Hub	Needs Hubs
Difficult to locate faults	Introduction of Hub makes fault finding much easier
Terminators needed	Terminators not needed
The cabling is comparatively less reliable	Inherently much reliable
Single segment length (node to node) up to 180 meters	Single segment length up to 200 meters

 

Comparison between Twisted Pairs and Co-Axial Cable

Unbound Transmission Media

Unbound transmission media extend beyond the limiting confines of cabling. They provide an excellent communication alternative for WANS. The lack of physical restrictions provides larger bandwidth as well as wide area capabilities. Unbound media typically operate at very high frequencies. The three types of unbound transmission media are: Radio wave, Micro wave, Infrared

Radio Wave

Although Radio waves are prevalent and well understood, we are just beginning to realize their enormous potential as a networking medium. Radio waves can operate on a single or multiple frequency bands.

Microwave

Microwaves have been used in data communications for a long time. They have a higher frequency than radio waves and therefore can handle larger amounts of data.

Microwave transmission is line of sight (LOS) transmission. The transmit station must be in visible contact with the receive station. This sets a limit on the distance between stations depending on the local geography. Typically the line of sight, due to the Earth’s curvature, is only 50 km to the horizon! Repeater stations must be placed so the data signal can hop, skip and jump across the country.

Microwaves operate at high operating frequencies of 3 to 10 GHz. This allows them to carry large quantities of data due to their large bandwidth.

Advantages of microwaves

1. They require no right of way acquisition between towers.
2. They can carry high quantities of information due to their high operating frequencies.
3. Low cost land purchase: each tower occupies only a small area.
4. High frequency/short wavelength signals require small antennae.
5. Attenuation by solid objects: birds, rain, snow and fog.
6. Reflected from flat surfaces like water and metal.
7. Diffracted (split) around solid objects.
8. Refracted by atmosphere, thus causing beam to be projected away from receiver.

Disadvantages of Microwaves

Infra Red

Infrared offers a great unbound photonic solution. Like fiber-optic cabling, infrared communications use light, so they are not bound by the limitations of electricity.

Types of Computer Network

Computer networks fall into three classes regarding the size, distance and the structure namely: LAN (Local Area Network), MAN (Metropolitan Area Network), and WAN (Wide Area Network). A LAN links a small group of functionally similar workstations within a local geographic area such as a series of adjacent cubicles or offices on the same floor. Once the network expands to include other floors or divers office within a metropolitan area, it becomes a MAN. Finally, a WAN is simply a LAN of LANs. WANs expand the boundaries of networking to a global or even galactic scale.

LAN

A LAN is a Local Area Network, within a single building or a specific confined space. LANs typically comprise only one transmission media type such as coaxial cable or twisted pair. LANs are characterized by comparatively high-speed communications. These high speeds are possible because LANs use one kind of cable which generally is limited to 5 km or less.

MAN

MAN stands for Metropolitan Area Networks. MAN is larger than a LAN and as its name implies, covers the area of a single city. MANs rarely extend beyond 100 KM and frequently comprise a combination of different hardware and transmission media.

The two most important components of MANs are security and standardization. Security is important because information is being shared between dissimilar systems. Standardization is necessary to ensure reliable data communication.

WAN

A wide area network is simply a LAN of LANs. WANs connect LANs that may be on opposite sides of a building, across the country or around the world. WANS are characterized by the slowest data communication rates and the largest distances. WANs can be of two types: an enterprise WAN and Global WAN.

Enterprise WANs

An enterprise WAN connects an entire organization including all LANs at various sites. This term is used for large, widespread organizations such as corporations, universities and governments.

Global WANs

Global WANs also span the world but they do not have to connect LANs within a single organization. The Internet is an example of a global WAN. It connects diverse locations, organizations and institutions throughout the world. Global WANs can be public or private. Private WANs are called Intranet which belongs to an organization. Public WANs are open to everybody so that anybody can connect and use the resources and services available.

The two types of LAN

There are basically two types of Local Area Networks namely: Arcnet and Ethernet.

Protocols

The term protocol refers to a set of rules and procedures that govern the transmission of messages over a physical networking medium. The most common network protocols are: (a) TCP/IP, (b) IPX/SPX and (c) NetBEUE

Major Network Protocols

The three major network protocols are:

1. TCP/IP
2. IPX/SPX (Used in Novell Netware)
3. NetBEUE (Product of Microsoft Co.)

LAN Topologies

The term topology defines the geographic arrangement of networking devices. It describes the actual layout of the network hardware. Given the location of workstations and peripherals, the goal of topology is to find the most economical and efficient way to connect all the users to the network resources while providing adequate capacity to handle user demands, maintain system reliability and minimize delay.

The selection of a topology for a network cannot be done in isolation as it affects the choice of media and the access method used. Because it determines the strategy used in wiring a building for a network and deserves some careful study.

The two network connection types

The two different network connection types are (a) point-to-point connection and (b) multipoint connection.

Point-to-Point connection type

A point-to-point connection is a direct link between two devices such as a computer and a printer. Most of today’s point-to-point connections are associated with modems and PSTN (Public Switched Telephone Network) communications.

Multipoint connection

A multipoint connection is a link between three or more devices. Historically, multipoint connections were used to attach central CPs to distributed dumb terminals. In today’s LAN environments, multipoint connections link many network devices in various configurations.

Basic LAN Topologies

The three simple LAN topologies that are combined to form any practical topology are known as basic LAN topologies. They are, Bus Topology, Ring Topology and Star Topology.

Explain Bus Topology.

The physical Bus topology is the simplest and most widely used of the network designs. It consists of one continuous length of cable (trunk) and a terminating resistor (terminator) at each end. Data communication message travels along the bus in both directions until it is picked up by a workstation or server NIC. If the message is missed or not recognized, it reaches the end of the cabling and dissipates at the terminator.

 

 

All nodes on the bus topology have equal access to the trunk. This is accomplished using short drop cables or direct T-connectors. The number of devices and the length of the trunk can be easily expanded.

The Advantages of Bus Topology

The advantages of physical bus topology are:

1. It uses established standards and it is relatively easy to install.
2. It requires less media than other topologies.

The Disadvantages of Bus Topology

The disadvantages of bus topology are:

1. The bus networks are difficult to reconfigure, especially when the acceptable number of connections or maximum distances have been reached.
2. They are also difficult to troubleshoot because everything happens on a single media segment. This can have dangerous consequences because any break in the cabling brings the network to its knee.

Ring Topology

The physical ring topology is a circular loop of point-to-point links. Each device connects directly to the ring or indirectly through and interface device or drop cable. Message travel around the ring from node to node in a very organized manner. Each workstation checks the message for a matching destination address. If the address doesn’t match the node simply regenerates the message and sends it on its way. If the address matches, the node accepts the message and sends a reply to the originating sender.

Advantages of Ring Topology

The advantages of ring topologies are:

1. They are very easy to troubleshoot because each device incorporates a repeater.
2. A special internal feature called beaconing allows troubled workstations to identify themselves quickly.

Disadvantages of Ring Topology

The disadvantages of ring topologies are:

1. It is considerably difficult to install and reconfigure ring topology
2. Media failure on unidirectional or single loop causes complete network failure.

Star Topology

The physical star topology uses a central controlling hub with dedicated legs pointing in all directions – like points of a star. Each network device has a dedicated point-to-point link to the central hub. This strategy prevents troublesome collisions and keeps the lines of communications open and free of traffic.

This topology, obviously, require a great deal of cabling. This design provides an excellent platform for reconfiguration and trouble-shooting. Changes to the network are as simple as plugging another segment into the hub and a break in the LAN is easy to isolate and doesn’t affect the rest of the network.

Benefits of Star Topology

The benefits of star topology are:

1. Relatively easy to configure.
2. Easy to troubleshoot
3. Media faults are automatically isolated to the failed segment.

Disadvantages of Star Topology

The disadvantages are considered as follows:

1. Requires more cable than most topologies.
2. Moderately difficult to install.

Popular topologies other than basic Topologies

Apart from basic topologies some other topologies worth considering are: mesh topology (every device connected to all other devices), Cellular Topology (wireless point to pint and multipoint design), Tree Topology (Hierarchical connections of devices), Hybrid topology (combination of two or more basic topologies).

Network Standards

Protocol (the logical component) and Topology (the physical component) is combined together to create a networking standard. These standards are developed and controlled by the Institute of Electrical and Electronics Engineers (IEEE).

Major industry standards

The four major industry standards are (a) Ethernet, Token Ring, ARCNet and FDDI (Fiber Distributed Data Interface).

Ethernet

The Ethernet topology was developed at the University of Hawaii to connect computers on the various Islands. It was radio based design. Later, Robert Metacalfe went to Xeros’s Palo Alto Research Center (PARC) laboratories and eliminated the radio portion and changed to co-axial cabling. Ethernet is one of the most popular LAN technologies in use today covering more than 85% of the networks. Ethernet system consists of three basic elements:

1. The physical medium use to carry Ethernet signals between computers on the network
2. A set of rules (protocols) embedded in each Ethernet interface that will decide how multiple computers on the network will have access to the data on the medium.
3. An Ethernet frame that consists of a standardized set of bits used to carry data over the system.

Ethernet Worked

The operation of Ethernet can be described in simple terms as follows:

Each computer on the Ethernet Network, also known as a node, operates independently of all other nodes. All nodes attached to an Ethernet are connected to a shared medium over which the Ethernet signals travel serially, one data bit at a time.

To send data a station first listens to the channel and when the channel is idle the station transmits its information in the form of an Ethernet frame, or packet. The Ethernet rules (protocol) are defined in such a way that every node gets a fair amount of frame transmission opportunity.

As each Ethernet frame is sent out on the shared medium, the Ethernet interfaces inside the node look at the destination address. The interfaces compare the destination address of the frame with their own address. The Ethernet interface with the same address as the destination address in the frame will read the entire frame and all other network interfaces will ignore the information.

What is Medium Access Control of Ethernet?

The set of rules which ensures that every node in an Ethernet gets a fair amount of frame transmission opportunity, are called the “Medium Access Control” mechanism. The Medium Access Control mechanism is based on a system called Carrier Sense Multiple Access with Collision Detection (CSMD/CD).

Explain Ethernet Frame.

The heart of Ethernet system is the Ethernet Frame, which is used to deliver information between the computers. The frame consists of a set of bits organized into several fields. These fields include address fields, a data field and an error checking field that checks the integrity of the bits in the frame to make sure that the frame has arrived intact.

Advantages of Ethernet

Ethernet’s major advantages are:

1. It is an inexpensive way to achieve high speed LAN transmissions (10 to 100 MB/s)
2. It is a proven technology that supports various writing configurations.
3. It works well with a large number of LAN and micro-to-mainframe applications.
4. It is easy to install.

What are the disadvantages of Ethernet Cabling?

The Ethernet cabling ahs the following disadvantages:

1. Ethernet is not a high-level performer in high-load environments. This protocol (CSMA/CD: Carrier Sense Multiple Access/Collision Detection) can slow down dramatically if hundreds of workstations are competing for the same cabling trunk
2. Its linear bus cabling system can sometimes make it difficult to isolate problems.

ARCNet

The Attached Resource Computer Network (ARCNet) standard was created in 1977 at the Data Point Corporation by a scientist – John Murphy. ARCNet uses the token-passing protocol over a star and bus topology. The star and bus topology combines the flexibility of a star with the simplicity and throughput of a bus. Thus, ARCNet standard has a unique protocol/topology combination: token-passing protocol and Distributed star/bus topology.

Advantages of ARCNet

Here are some of the ARCNet’s advantages:

1. It is extremely reliable.
2. ARCNet is easy to install and troubleshoot.
3. It has an excellent track record of interoperability for those using ARCNet components from various manufacturers.
4. ARCNet supports a variety of cable types including coaxial, UTP and Fiber Optics.
5. It is inexpensive and built to stay that way.

Disadvantages of ARCNet

Here are some disadvantages of ARCNet:

1. Standard ARCNet is very slow (2.5 Mb/s). It is almost seven times slower than Token Ring.
2. ARCNet was not designed with interconnectivity in mind. For many installations, it’s difficult to go beyond the confines of single LAN.

Token-Passing Protocol

The token-passing protocol relies on a control signal called the token. A token is a 24-bit packet that circulates throughout the network from NIC to NIC in an orderly fashion. If a workstation wants to transmit a message, first it must seize the token. At that point, the workstation has complete control over the communications channel. The existence of only one token eliminates the possibility of signal collisions. This means that only one station can speak at a time.

Logical Ring Physical Star topology for Token-Passing Standard

It is sure that any break in the ring at any point will interrupt communications for all machines. To solve this problem, IBM developed a modified ring topology, which they called the logical ring physical star. The central point of the physical star configuration is Token Ring hub called the multi-station access unit (MSAU, pronounced as masow). Workstations and servers attached to the MSAU through special STP adapter cables. IBM converted stars into a logical ring by connecting all MSAU hubs together through special ring-in (RI) and ring-out (RO) ports.

Advantages of Token Ring

Here are Token ring’s most useful advantages:

1. It offers excellent throughput under high-load conditions.
2. Token Ring facilitates LAN-to-LAN mainframe connections especially for interfacing with IBM’s broader connectivity strategies.
3. It has built-in troubleshooting mechanisms such as beaconing and auto-reconfiguration and may now be used with UTP cabling.
4. It has the most reliable protocol (token-passing), the most trouble-free configuration (physical star) and the fastest connectivity scheme (r or 16 mb/s).

Point out the disadvantages of Token Ring.

Few of the disadvantages of Token Ring are:

1. Token Ring is very expensive. All topology components cost much more than other more popular standards.
2. It is relatively proprietary. Token Ring’s complexity is built into the hardware components. This means hat you need to choose a manufacturer and stick with it.
3. Engineers must have considerable expertise to manage and troubleshoot token ring components.

Beaconing and Auto-Reconfiguration

When a station does not receive a message from its nearest active upstream neighbor, it sends out a warning, otherwise known as a beacon. This beacon alerts everyone that something is wrong and helps to isolate the failure domain. When beacon occurs, the ring will attempt to fix the problem without your intervention. This process of self-healing is called auto-reconfiguration.

Network Architecture

When two or more computer are connected with one another for the purpose of communicating data electronically, besides physical connection of computers, communication devices and system servers, a well defined standard known as architecture is required to establish cohesive communication between devices in Network.

Popular Network Architectures

The most popular architectures are:

1. ISO Open System Architecture (OSI)
2. IBM’s System Network Architecture (SNA)

ISO’s OSI Architecture

The Open System Interconnection (OSI) is a standard reference model for communication between two end users in a network. It is used in developing products and understanding networks which means commonly used Internet product and services fit within the model. The OSI model describes seven layers of related functions that needed at each end, when a message is sent from one party to another party in a network. Each layer has its own set of special related function as follows:

Layer 7 – Application Layer: Application programs that use the network.

Layer 6 – Presentation Layer: Standardize data presented to the application.

Layer 5 – Session Layer: Manages sessions between applications

Layer 4 – Transport Layer: Provides error detection and correction

Layer 3 – Network Layer: Provides data delivery across the physical connection

Layer 2 – Data Link Layer: Provides data delivery across the physical connection

Layer 1 – Physical Layer: Defines the physical network media.

IBM’s SNA Architecture

SNA is a computer networking architecture that was developed by IBM to provide a network structure for IBM mainframe, midrange, and personal computer systems. SNA defines a set of proprietary communication protocols and message formats for the exchange and management of data on IBM host networks.

• SNA can be used for the following types of tasks:
• Terminal access to mainframe and midrange computer applications.
• File transfer of data between computer systems.
• Printing of mainframe and midrange data on SNA printers.
• Program-to-program communications that allow applications to exchange data over the network.
• SNA can be implemented in a networking infrastructure that uses either a hierarchical or peer-to-peer model.

Networking Model

Peer-to-Peer Networking Model

A networking model where each workstation has equivalent capabilities and responsibilities is known as peer-to-peer model. There is no central server in this network and computers join hands to share files, printers and Internet access. It is practical for workgroups of a dozen or less computers making it common environments, where each PC acts as an independent workstation that stores data on its own disk but which can share it with all other PCs on the network. Software for peer-to-peer network is included with most modern desktop operating systems such as Windows and Mac OS.

Client/Server Networking Model

A networking model where one or more powerful computers (servers) provide the different network services and all other user’s computers (clients) access those services to perform user’s tasks is known as client/server networking model. Client-server networking model became popular in the late 1980s and early 1990s as many applications were migrated from centralized minicomputers and mainframes to networks of persona computers. The design of applications for a distributed computing environment required that they effetely be divided into two parts: client (front end) and server (back end). The network model on which they were implemented mirrored this client-server model with a user’s PC (the client) typically acting as the requesting machine and a more powerful server machine to which it was connected via either a LAN or a WAN acting as the supplying machine. It requires special networking operating system. It provides user level security and it is more expensive.

Network and Internet Terminologies

NICs

Network interface cards, commonly referred to as NICs are used to connect a PC to a network. The NIC provides a physical connection between the networking medium and the computers’ internal bus, and is responsible for facilitating an “access method” to the network. Most NICs are designed for a particular type of network, protocol and media, although some can serve multiple networks.

Hubs/Repeaters

Hubs/Repeaters are used to connect together two or more network segments of any media type. In larger design, signal quality begins to deteriorate as segment exceeds their maximum length. A hub provides the signal amplification required to allow a segment to be extended a greater distance. Passive hub simply forwards any data packets they receive over one port from one workstation to all their remaining ports. Active hubs, also sometimes referred to as “multiport repeaters”, regenerate the data bits in order to maintain a strong signal.

Bridges

The bridge function is to connect separate homogeneous networks. Bridges map the Ethernet address of the nodes residing on each network segment and allow only necessary traffic to pass through the bridge. When a packet is received by the bridge, the bridge determines the destination and source segments. If the segments are different, then the packet is “forwarded” to the correct segment. Bridges are also called “store-and-forward” device because they look at the whole Ethernet packet before making filtering or forwarding decisions.

Router

Routing achieved commercially popularity in the mid – 1980s – at a time when large-scale Internetworking began to replace the fairly simple, homogeneous environments. Routing is the act of moving information across an Internetwork from a source to a destination. It is often contrasted with bridging, which perform a similar function. Routers use information within each packet to route it from one LAN to another, and communicate with each other and share information that allows them to determine the best route through a complex network of many LANs.

Switches

LAN switches are an expansion of the concept in LAN bridging, which controls data flow, handles transmission errors, provides physical addressing, and manages access to the physical medium. Switches provide these functions by using various link-layer protocols. LAN switches can link four, six, ten or more networks together. A store-and-forward switch, on the other hand, accepts and analyses the entire packet before forwarding it to its destination.

Transceivers

Transceivers are used to connect nodes to the various Ethernet media. Most computers and network interface cards contain a built-in 10BaseT or 10Base2 transceiver, allowing them to be connected directly to Ethernet without requiring an external transceiver. Many Ethernet devices provide an AUI connector to allow the user to connect to any media type via an external transceiver.

 

Gateway

A Gateway is a device such as a mini or microcomputer capable of operating on a standalone basis but which also provides connection for communication with the other computers and access to shared resources.

Proxy Server

Also called a proxy or application level gateway. It is an application that breaks the connection between sender and receiver. Thus, it helps us to prevent hacker from obtaining Internet address and detail of a private network.

Firewall

Firewall is a method for keeping a network secure. It is mostly used in giving users access to the Internet in a secure fashion as well as to separate a company’s public web server from its internal network.

Node

A node is a hardware device or group of devices or station in a network that link one or more other unit to the network.

Wireless Network

The most and latest wireless LANs use electromagnetic airwaves either infrared or radio frequency to communicate information from one point to another without relaying on a physical connection. Radio waves are often referred to as radio carriers because they simply perform the function of delivering energy to a remote receiver. The data being transmitted is superimposed on the radio carrier so that it can be accurately extracted at the receiving end. Multiple radio carriers can exist in the same space at the same time without interfering with each other if the radio waves are transmitted on different radio frequencies.

In a typical WLAN configuration, a transmitter/receiver (transceiver) device, called an Access Point (AP), connects to the wired network from a fixed location using standard Ethernet cable. The Access Point receives, buffers, and transmits data between the WLAN and the wired network infrastructures. A single Access Point can support a small group of users and can function within a range of less than one hundred to several hundred feet. The Access Point (or the antenna attached to the Access Point) is usually mounted high but may be mounted essentially anywhere that is practical as long as the desired radio coverage is obtained. The wireless network, printers or other peripherals can be shared through a connected PC. The devices then communicate using a set of reserved high-frequency radio waves. An Access Point device connects to a DSL or cable modem and enables high-rate (broadband) Internet access for the entire network.

Internet

Internet is the large worldwide network of computes that facilitates data communication services, file transfer, electronic mail, World Wide Web and newsgroup with common protocols.

WWW

The WWW is the brainchild of Tim Berners Lee a CERN who had the idea of creating an electronic web of research information. The web is currently the fastest growing Internet information system, with new resources being added regularly. The web relies on a set of protocols, conventions and software to operate. The web is a distributed system of delivering linked documents over the Internet. It is called a distributed system because information can reside on different computers around the world. Yet be easily linked together using hypertext. The web uses hypertext to create links from together using hypertext. The web uses hyperte3xt to create links from one resource to another. A hypertext link is usually displayed by highlighted and underlined text on the page. A hypertext link or hyperlink can also be graphic that acts as a button linking to another resource.

IRC

Internet Relay Chat (IRC) is a system for sending public and private message to other users in “real time” – that is, your message appears on the recipient’s screen as soon as you type it.

CU-SeeMe

CU-SeeMe is a video conferencing system that allows users to send and receive sound and pictures simultaneously over the Internet.

Telnet

It is a protocol or set of rules that enables a computer to connect another computer in network. It is also known as a remote login. The telnet operates on client-server principle.

Gopher

The ghoper is a protocol designed to search, retrieve and display documents from remote sites on the Internet. The Ghoper was created as a piece of software to utilize some of the services that were becoming available on the Internet.

HTML

HTML stands for Hyper Text Markup Language. It is a standard coding language used to create all web documents (pages).

Browsers

A browser is the Internet Client software that acts as an interface between the user and the inner-workings of the Internet, specifically the WWW. We can find graphical web browser that displays multimedia content of text, graphics, audio and video, and text web browser that displays only text. Internet Explorer, Netscape, Firefox are graphical web browser and Lynx is a well known text browser.

Dialup Connection

Dialup connection is a means of connecting user to another computer (ISP) or a network such as the Internet with a modem equipped computer.

IP Address

IP Address is an identifier for particular machine on a particular network. It is part of scheme to identify computers on the Internet. IP addresses are a set of numbers separated with periods.

Domain Name

A domain name is a way to identify and locate computers connected to the Internet. This is a text name of a computer in network or Internet. Domain names are converted to IP Addresses to locate computers and resources.

URL

URL stands for Uniform Resource Locator that identifies a particular Internet resource. URL help the user to locate web page, gopher service, library catalog and image or text file locations. URLs are the standard addressing system of the www. A complete URL provides the web client with all the information it needs to contact a server and make a request for information. URLs are divided into three basic parts:

Example: http://www.psexam.com/download.htm

1. Protocol (http://) – The information appearing before the colon in any URL indicates the type of information server or protocol. For example http:// indicates that the server to be connected is a www server.
2. Domain name (www.psexam.com) – The second piece of information is the address of the server. In this example psexam.com is the name of the machine at PS Exam in world wide web.
3. Resource name (download.htm) – The third piece of information is the path to the actual document requested. In this example the URL indicates that the document in the system directory and is named download.htm.

Web Browsing or Surfing

Browsing or Surfing is the process of visiting different web sites on the Internet hosted by various organizations.

Search Engine

The search engine is an interactive tool to help people locate information via the www and it is interface between the user and underlying database. The most popular search engines are Alta Vista Exite, Lycos, Yahoo!, Google, Ask etc.

Meta Search Engine

A web meta searcher is a tool that helps users to locate information available via the World Wide Web. Web meta-serchers provide a single interface that enables users to search many different search engines, indexes and databases simultaneously. Some meta search engines are Albany.net, Clnet (search.com), Cyberland, Eureaka!, Savvysearch and so on.

Internet Access

We can access to the Internet in one of two basic ways, dialing into an Internet Service Provider’s (ISP) computer or with a direct connection to an ISP. Connecting to ISP by dialing their hunting number (phone number) is called Dial-up connection. We require a username, password and ISP’s hunting number to configure Dial up Connection.

Extranet

An Extranet is a type of Intranet (Internal TCP/IP Network) that has been selectively opened to a firm’s suppliers, customers.

Intranet

An intranet can be defined as a network connecting an affiliated set of clients using standard internet protocols, esp. TCP/IP and HTTP or as an IP-based network of nodes behind a firewall, or behind several firewall connected by secure, possibly virtual, networks.

Web Index

A web index is designed to assist users in locating information on the World Wide Web. Web indexes are also referred to as catalogs or directories. A web index collects and organizes resources available via the www. Some of the web indexes are Yahoo!, Megallan, Apollo etc.

Hypertext

The hypertext allows for the integration of text, graphics, audio and video on a web pate. This can make it very easy to browse and very exciting to view. A web page may have colorful graphics integrated with textual information. Links on a web page may take you to other web pages, recorded sonds, or digital video clips. A single click on any hyperlink allows you to follow the link to the specified resource.

Email

Electronic Mail (Email) is one of the most popular & powerful communication tools on the Internet. It is an efficient and effective means of network communication. Email allows you to communicate with people across the globe via electronic media (computer).

Email address

An Email Address identifies a person and the computer for the purpose of exchanging electronic mail message.

Example:

The email address contains three parts:

1. Username – The admin in example.
2. Domain name of organization – The psexam in example
3. Top Level Domain – The com in example

Figure 56: Email Client Interface

Inbox

It is an element of Email Application which collects all incoming mails.

Outbox

It is an element of Email Application which collects all outgoing mails, if it is created and sent in offline.

Trash

This is an element of Email Application that holds all the deleted emails.

CC

CC stands for Courtesy copy or Carbon Copy. It is an element of Email used to specify the additional recipients when the mail sent needs to be acknowledged to them.

BCC

BCC stands for Blank Carbon Copy. It is similar to CC but the address of other receivers will not be shown to the receiver.

Reply

A reply is the response of an email you receive. After you read a mail and need to reply it you can use this feature.

Forward

A mail received can be sent to be other recipients known as forwarding.

Attachments

The documents created in other applications such as word, excel can be sent along with the email message. These documents that are sent with email is known as attachment. Documents, audio/video files, Zip files etc. can be sent as attachment along with email message.

Bounced

When a mail sent can’t reach to destination and returns back, this is known as bounced. This happens often when the recipient’s address is wrong or the server at the recipient’s end is down or recipient’s inbox is full.

Netiquette

It is essential for all users on the internet to recognize that they are responsible for their own individual actions while using the net. Netiquette is simply the use of common courtesy and polite behavior while using the net.

Emoticons

The convention of expressing feeling or a joke in symbolic form by user in Email or Chatting for example 🙂 for smiling 😉 for winking 🙁 for frowning etc are emoticons.

Figure 58: Emoticons

Points to Remember