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Q. 1 Explain the meaning of Data communication?

Answer-Data communication is the exchange of data between two devices via some form

of transmission medium such as wire cable. The effectiveness of a data communication

system depends on three fundamental characterstics :-

Delivery :- The system must deliver data to the correct destination. Data

must be received by the intended device or user and only by that device or user.

Accuracy :- The system must deliver the data accurately.

Timeliness :- The system must deliver data in a timely manner.

A Data Communication System has five components:-

(1) Message : The message is the information (data) to be communicated. It

can consist of text, numbers, pictures, sound or video or any

combination of these.

(2) Sender : The sender is the device that sends the data message.

(3) Receiver : The receiver is the device that receives the message.

(4) Medium : The transmission medium is the physical path by which a

message travels from sender to receiver.

(5) Protocol : A protocol is a set of rules that governs data communication.

Q. 5. What do you mean by variable, expression and functions in JavaScript.

Answer-Variables are the named value holders.They act as a container to store the

value.To declare the variable we will use the var keyword. The general form is , var

variablelist; e.g. var a,b,c;

Types of values :

1) integer values : The values without the fractional part .e.g. 10,-45 etc...

2) real values : The values which contains the fractional part e.g. 5.6,7.89 etc...The real

values are also known as the floating point values.

3) character values : It refers to the single character. e.g. 'a','%','3' etc...

4) string values : It refers to the group of characters. "ajay" etc...

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Q. 6 Write short Notes on

Answer-(i) WAN :-WANis a collection of computers and network resources connected

via a network over a geographic area. Wide-Area Networks are commonly connected

either through the internet or special arrangements made with phone companies or other

service providers. A WAN is different from a MAN because of the distance betweeneach of the networks. In a WAN, one network may be anywhere from several hundred

miles away, to across the globe in a different country.

For home routers the port the router connects to your Internet connection is often labeled

as aWAN,Internetport, since it is what allows your home network to communicate with

the Internet network. In the below picture, is an example of the Internet port on the back

of a home router, next to four standard Ethernet ports.

(ii) FTP:-File Transfer Protocol, is a protocol through which internet users can upload

files from their computers to a website or download files from a website to their PCs.

Originated by Abhay Bhushan in 1971 for use in the military and scientific researchnetwork known as ARPANET, FTP has evolved into a protocol for far wider applications

on the World Wide Web with numerous revisions throughout the years.

FTP is the easiest way to transfer files between computers via the internet, and

utilizes TCP, transmission control protocol, and IP, internet protocol, systems to perform

uploading and downloading tasks.

How It Works

TCP and IP are the two major protocols that keep the internet running smoothly. TCPmanages data transfer while IP directs traffic to internet addresses. FTP is an underling of

TCP and shuttles files back and forth between FTP server and FTP client. Because FTP

requires that two ports be open--the server's and the client's--it facilitates the exchange of

large files of information.

First, you as client make a TCP control connection to the FTP server's port 21 which will

remain open during the transfer process. In response, the FTP server opens a second

connection that is the data connection from the server's port 20 to your computer.

Using the standard active mode of FTP, your computer communicates the port numberwhere it will stand by to receive information from the controller and the IP address--

internet location--from which or to which you want files to be transferred.

If you are using a public--or anonymous--FTP server, you will not need proprietary sign-

in information to make a file transfer, but you may be asked to enter your email address.

If you are using a private FTP server, however, you must sign in with a user name and

password to initiate the exchange of data.

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Modes of File Transfer

Three modes of transferring data are available via FTP. The system can use a stream

mode, in which it transfers files as a continuous stream from port to port with no

intervention or processing of information into different formats. For example, in a

transfer of data between two computers with identical operating systems, FTP does not

need to modify the files.

In block mode, FTP divides the data to be transferred into blocks of information, each

with a header, byte count, and data field. In the third mode of transfer, the compressed

mode, FTP compresses the files by encoding them. Often these modifications of data are

necessary for successful transfer because the file sender and file receiver do not have

compatible data storage systems.

Passive FTP

Should your computer have firewall protection, you may have difficulties using FTP. A

firewall protects your PC by preventing internet sites from initiating file transfers. You

can circumvent your firewall's function by using the PASV command that reverses the

FTP process, allowing your computer to initiate the transfer request.

Many corporate networks use PASV FTP as a security measure to protect their internal

network from assaults of unwanted external files. Also called passive FTP, the process

requires that any transfer of information from the internet or other external source must

be initiated by the client or private network rather than the external source.

Further FTP Security

In response to the need for a more secure transfer process for sensitive information such

as financial data, Netscape developed a Secure Sockets Layer (SSL) protocol in 1994 that

it used primarily to secure HTTP--HyperText Transfer Protocol--transmissions from

tampering and eavesdropping. The industry subsequently applied this security protocol to

FTP transfers, developing SFTP, a file transfer protocol armored with SSL for protection

from hackers.

Q. 7 Explain the concept of Telnet.

Answer-Telnet is a protocol that allows you to connect to remote computers (called

hosts) over a TCP/IP network (such as the Internet). Using telnet client software on your

computer, you can make a connection to a telnet server (i.e., the remote host). Once your

telnet client establishes a connection to the remote host, your client becomes a virtual

terminal, allowing you to communicate with the remote host from your computer. In

most cases, you'll need to log into the remote host, which requires that you have an

account on that system. Occasionally, you can log in as guest or public without having an

account.

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Telnet clients are available for all major operating systems.

Command-line telnet clients are built into most versions of Mac OS X, Windows, Unix,

and Linux. To use these clients, go to their respective command lines (i.e., the Terminal

application in Mac OS X, the shell in Unix or Linux, or the DOS prompt in Windows),

and then enter:

telnet host

Replace host with the name of the remote computer to which you wish to connect.

Q. 8 What are advantage and disadvantage of E-commerce?

Answer-Advantage of ecommerce:-

1. Facilitates the globalization of business:-e commerce facilitates theglobalization of business by providing some economical access to distantmarkets and by supporting new opportunities for firms to increase economies by

distributing their products internationally.

2. Provides increased purchasing opportunities for the buyer:-As e commerceincreases sales opportunities for the seller, it also increases purchasing

opportunities for buyer.

3. Lowering staffing cost:- As in e commerce, the selling & purchasing process isoutline, the amount of interaction with staff is minimized.

4. Market based expansion: - An e commerce is open to entirely new group ofusers, which include employees, customers, suppliers & business partners.

5. Increased profits:-With ecommerce, companies reach more & more customerswhere physical commerce cannot reach, thus increasing profits.

6. Increased customer service & loyality:- e commerce enables a company to beopen for business wherever a customer needs it.

7. Increase speed & accuracy:- E commerce see the speed and accuracy withwhich business can exchange information, which reduces cost on both sides of

transactions. It is available 24 hours a day & 7 days a weak.

8. ReIncreased customer service & loyalityIncrease speed & accuracyRduction ofpaper storage.

9. Increased response times:- In e commerce, the interaction with the system takeplace in real time & therefore allows customer or bidder to respond more quickly

& thus reduces the time of discussion between then as in traditional commerce.

Limitations of ecommerce:-

1. Security:- the security risk in ecommerce can be :-

i. client / server riskii.

data transfer and transaction risk

iii. virus risk

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2. High start up cost:-

The various components of cost involved with ecommerce are:-

A) Connection:- connection cost to the internet.B) Hardware / software:- this includes cost of sophisticated computer, moduer,

routers, etc.C) Maintenance:- this include cost involve in training of employees and maintenanceof web-pages.

3. Legal issues: - these issues arise when the customer data is fall in the hands of

strangers.

4. Lack of skilled personnel:- there is difficulty in finding skilled www developers and

knowledgeable professionals to manage and amaintain customer on line.

5. Loss of contact with customers:-Sometimes customers feel that they do not have

received sufficient personal attention.

6. Uncertainity and lack of information:- most of the companies has never used any

electronic means of Communication with its customers as the internet is an unknown

mode for them.

7. Some business process may never be available to e commerce:-Some items such as

foods, high cost items such as jewellery may be impossible to be available on the

internet.

Q. 9 Describe Electronic payment system.

Answer-

Electronic Payment (also known as c-money, electronic cash, electronic currency,digital money, digital cash or digital currency) refers to money or scrip which isexchanged only electronically.

Typically, this involves use of computer networks, the internet and digital storedvalue systems.

Electronic Funds Transfer (EFT) and direct deposit are examples of electronicpayment.

Also, it is a collective term for financial cryptography and technologies enablingit.

The components of Electronic Payment system are described as below in details: COMPUTER Network:

A computer network is a group of interconnected computers. Network s may beclassified according to a wide variety of characteristics.

Based on their scale, networks can be classified as Local Area Network (LAN),Wide Area Network (WAN), Metropolitan Area Network (MAN), Personal Area

Network

(PAN), etc. Computer networks can also be classified according to the hardware and software

technology that is used to interconnect the individual devices in the network, such

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as Optical fibre, Ethernet, Wireless LAN, Home PNA, or Power line

communication. Ethernet uses physical wiring to connect devices. Frequently

deployed devices include hubs, switches, bridges and/or routers.

Wireless LAN technology is designed to connect devices without wiring. Thesedevices use radio waves or infrared signals as a transmission medium. Computernetworks may be classified according to the functional relationships which exist

among the elements of the network, e.g., Active Networking, Client-server and

Peer-to-peer (workgroup) architecture.

Computer networks may be classified according to the network topology uponwhich the network is based, such as Bus network, Star network, Ring network,

Mesh network, Star-bus network.

Tree or Hierarchical topology network, Network Topology signifies the way nwhich devices in the network see their logical relations to one another. The use of

the term logical here is significant.

That is, network topology is independent of the physical layout of the network.Even if networked computers are physically placed in a linear arrangement, if

they are connected via a hub, the network has a Star topology, rather than a Bus

Topology, in this regard the visual and operational characteristics of a network

are distinct; the logical network topology is not necessarily the same as the

physical layout.

Internet:

The Internet is a specific internet work. It consists of a worldwide incomingconnection of governmental, academic, public, and private networks based upon

the networking technologies of the Internet Protocol Suite.

It is the successor of the Advanced Research Projects Agency Network(ARPANET) developed by DARPA of the U.S. Department of Defense.

The internet is also the communications backbone underlying the World WideWeb (WWW).

The Internet is most commonly spelled with a capital I as a proper noun, forhistorical reasons and to distinguish it from other generic internet works.

Participants in the Internet use a diverse array of methods of several hundreddocumented, and often standardized, protocols compatible with the Internet

Protocol

Suite and an addressing system (IP Addresses) administered by the InternetAssigned Numbers Authority and address registries.

Service providers and large enterprises exchange information about the reachability of their address spaces through the [Border Gateway Protocol] (BGP),

forming a redundant worldwide mesh of transmission paths.

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3.) BASIC HARDWARE COMPONENTS:

All networks are made up of basic hardware b11ing blocks to interconnectnetwork nodes, such as Network Interface Cards

(NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually

in the form of galvanic cable (most commonly Category 5 cable.

Less common are microwave links (as in IEEE 802.11) or optical cable (opticalfibre).

NETWORK Interface Cards

A network card, network adapter or NIC (network interface card) is a piece ofcomputer hardware designed to allow computers to communicate over a computer

network. It provides physical access to a networking medium and often provides a low-

level addressing system through the use of MAC addresses.

It allows users to connect to each other either by using cables or wirelessly.REPEATER

Repeater is an electronic device that receives a signal and retransmits it at ahigher rate, or to the other side of an obstruction, so that the signal can cover

longer distances without degradation.

In most twisted pair Ethernet configurations, repeaters are required for cable runslonger than 100 meters away from the computer.

HUBS

A Hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub for

transmission.

When the packets are copied, the destination address in the frame does not changeto a broadcast address. It does this in a rudimenJ ary way:

It simply copies the data to all of the Nodes connected to the hub.Bridges

Network Bridge connects multiple network segments at the data link layer (layer2) of the OSI model.

Bridges do not promiscuously copy traffic to all ports, as hubs do, but learn whichMAC addresses are reachable through specific ports.

Once the bridge associates a port and an address, it will send traffic for thataddress only to that port. Bridges do send broadcasts to all ports except the one onwhich the broadcast was received.

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Bridges learn the association of ports and addresses by examining the sourceaddress of frames that it sees on various ports.

Once a frame arrives through a port, its source address is stored and the bridgeassumes that MAC address is associated with that port.

The first time that a previously unknown destination address is seen, the bridgewill forward the frame to all ports other than the one on which the frame arrived.

Bridges come in three basic types:

1. Local bridges: Directly connect local area networks (LANs)

2. Remote bridges: Can be used to create a wide area network (WAN) link between

LANs. Remote bridges, where the connecting link is slower than the end networks,

largely have been replaced by routers.

3.Wireless bridges: Can be used to join LANs or connect remote stations to LANs.

Switches

A switch is a device that performs switching. Specifically, it forwards and filters OSI layer 2 data grams (chunk of data communication) between ports (connected

cables) based on the MAC addresses in the packets.

This is distinct from a hub in that it only forwards the datagram to the portsinvolved in the communications rather than all ports connected.

Strictly speaking, a switch is not capable of routing traffic based on IP address(layer 3) which is necessary for communicating between network segments orwithin a large or complex LAN.

Some switches are capable of routing based on IP addresses but are still calledswitches as a marketing term.

A switch normally has numerous ports, with the intention being that most or theentire network is connected directly to the switch, or another switch that is in. turn

connected to a switch.

Switch is a marketing term that encompasses routers and bridges, as well asdevices that may distribute traffic on load or by application content (e.g., a Web

URL identifier).

Switches may operate at one or more OSI model layers, including physical, datalink, network, or transport (i.e., end-to-end).

A device that operates simultaneously at more than one of these layers is called amultilayer switch.

Routers

Routers are networking devices that forward data packets between networks usingheaders and forwarding tables to determine the best path to forward the packets.

Routers work at the network layer of the TCP/IP model or layer 3 of the OSImodel.

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Routers also provide interconnectivity between like and unlike media (RFC1812).

This is accomplished by examining the Header of a data packet, and making adecision on the next hop to which it should be sent (RFC 1812).

They use preconfigured static routes, status of their hardware interfaces, androuting protocols to select the best route between any two subnets.

A router is connected to at least two networks, commonly two LANs or WANs ora LAN and its ISPs network.

Some DSL and cable modems, for home (and even office) use, have beenintegrated with routers to allow multiple home/office computers to access the

Internet through the same connection.

Many of these new devices also consist of wireless access points (waps) orwireless routers to allow for IEEE 802.1 lg/b wireless enabled devices to connect

to the network without the need for cabled connections.