Internet and related terminology meaning

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Internet and related terminology meaning

1. INTERNET:-is a worldwide n/w of n/ws can be defined as a global n/w of over a million of smaller heterogeneous computer n/ws. The internet is the common language where by dissimilar computers with various operating systems, are able to communicate with each other ,using set of protocols(rules).

2. INTERNET SERVICE PROVIDERS(ISP’s):-worldwide offer various options and packages to the general public for internet access. ISP is a company which gives us the facility to gain access to the internet against a fee. Some ISP’s in INDIA are VSNL,MTNL,Mantra online etc.

3.INTERNET ADDRESSING:-Domain Name System-An addressing system was designed by the Internet Engineering Task Force(IETF).This addressing scheme assigns names and numbers to identify the computers on the internet. The names are called domain names and the numbers are called IP addresses. Domain name system(DNS) is a distributed database system for translating computer names into a numeric IP address. A domain name always contains two or more components separated by period called ‘dots’.IP addresses are in the number format xxx.xxx.xxx.xxx,where each xxx is a number from 0 to 255.IP addresses identify the host computers. IP address is called the host address.

4.WWW:-World Wide Web is a internet service, based on a common set of protocols, which allows a server computer to distribute documents across the Internet in a standard way. The WWW is an example of Client-Server technology. Internet user using a software known as the Web Browser ,requests a document located on the web. The browser acts like a customer or a client and requests for the information. The internet host serves the information and thus is called the Server. The flow of information is controlled by a protocol HTTP(Hyper Text Transport Protocol).

5.UNIFORM RESOURCE LOCATER(URL):-The technique used to address documents on the Web is called URL.It provides an addressing scheme which allow the browser to request about any document or web page.A URL normally takes the form

For example :-http:www.microsoft.com/IE/index.htm

Domain Name- An internet address which is character based is called a Domain Name.

6.Interspace: It is a client /server software program that allows multiple users to communicate online with real time audio, video and text chat in dynamic 3D environment.

7.Relative URL:-A Relative URL is not fully qualified ,but rather it inherits the protocol,host and path information from its parent document.They are used for accessing files when the full internet address is unnecessary.When Relative URL’s are accessed ,the base part of the URL is automatically

8. The different protocols for URL’s are-http://,HTML documents,gopher://Gopher menus and documents,news://usenet news group,telnet:Remote Telnet(login)Session

9.HTTP:- A web page is created by using a specialised language called HTML.(Hyper Text Markup Language).Web pages are requested by Internet users or clients from the internet host or servers and are served or transported over the internet using a protocol called HTTP(Hyper Text Transport Protocol).

10. Web Server:-It is the job of web server to accept connections from web browsers all over the internet and when requested ,send them the HTML documents that are available from your server.It is a computer with an internet connection that runs software designed to send out HTML pages and other file formats.

11. WEB SITE:- A web site is a collection of web pages belonging to a particular person or organization.

12. WEB PAGE:-A Web Page is single unit of information,,often called a document that is available via the worldwideWeb(WWW).A web page is an HTML document that is stored on a web server and that has a URL so that it can be accessed via a web. It is a document that uses HTTP.

WEB HOSTING- It is a means of hosting web server application on a computer system through which electronic content on the internet is readily available to any web browser client.

WEB PORTAL- It is a web site which hosts other web sites.

13. HOME PAGE(‘FRONT DOOR’):-The HomePage is the front door of the site and is set up to help viewers to find whatever is of interest of them on that site.The URL of the homepage also serves as the URL of the web site e.g. http://www.microsoft.com/ms.htm is a web site.

14. WEB BROWSER:-is a client application that requests,recieves and display HTML pages. It is a program that your computer runs to communicate with web servers on the internet, which enables it to download and display the web-pages that you request. The most popular browsers are –1.INTERNET EXPLORER 2.Netscape Navigator 3. NCSA MOSAIC

15.HTML:-Hyper Text Markup Language:-It is designed to specify the logical organization of a document,with important hypertext extensions.HTML instructions divide the text of a document into blocks called elements.These can be divided into two broad categories –those that define the body of the document is to be displayed by the browser ,and those that define information ‘about’ the document ,such as the title or relationships to other documents.

16.DHTML:-Dynamic HTML- is typically used to describe the combination of HTML ,style sheets and scripts that allows documents to be animated. The above of scripting add dynamism to the web page.

Difference: Web Pages created through HTML are static i.e. they appear the same every time they are viewed but web pages created through DHTML are dynamic i.e. their appearance may change upon viewing

17 XML:-Extended Markup Language-XML is a markup language for creating documents containing structured information.

Difference: In HTML both tag semantics and tag set are fixed but XML specifies neither semantics nor tagset. Rather it provides a facility to define tags and relationships among them.

18. E-mail(Electronic mail):- Advantages-(1).cost effective (2).instantaneous(very fast). ?(3). Offers non-intrusive medium (4).convenient to use (5).usability.

Limitations- (1).security and privacy of E-mail-Hackers can get access to your mail box. (2). Impersonal medium-difficult to express emotions

19.E-mail Address-E-mail address is made up of two parts:-the user name and the host name(fullu qualified Domain Name of the server or host on which user has an account).Two parts are separated by “@” symbol.No two persons can have same user name.

20. SEARCH ENGINES- are a Bottom-Up approach to find your way around the Web. You give a search engine a list of query and it returns to you a list of web pages that contain those words.It provides an interface between the use and the underlying database e.g.Alta Vista is one of the oldest search engines on the web. Excite , HOTBOT and Infoseek are some examples of Search Engines.

21. CHAT SERVICES-uses a specialised s/w that allows the user to type some comment in on window and receive some replies in another from someone who is accessing the same s/w.Web sites that enable you to converse with other web users are called CHAT .These sites are referred to as Chat rooms.

22. VOICE CONFERENCING & VIDEO CONFERENCING-Voice Conferencing is talking to another person via the microphone and speakers connected to your computer. Video Conferencing is sending your image and voice to one or more other people,through the camera and microphone attached to your computer.

23. DOWNLOADING & UPLOADING-The most popular form of file transfer is to download files from the web.The concept of uploading means to transfer files from your host computer to other computers through modem.Netscape Navigator and certain other browsers can also upload files.

24. (ELECTRONIC) E- COMMERCE-buying and selling of products and services over the Internet.

25. USENET-A system in which thousands of newsgroups enable to exchange news on huge subjects.They are the discussion groups in the internet ,where people gather to post messages and replies on thousands of topics.

FINDING THINGS ON INTERNET

26. ARCHIE-tries to locate files in public FTP archives.It searches for the file names or partial names.Archie searches its database and informs you about all the files that match.

27. VERONICA-one of the menu item of GOPHER. This tool takes you to the Gopher servers ,which contain specific information ,you are searching for.Veronica builds a special Gopher menu for you consisting of all the menu items in its databse that matches the words asked by you.

28. WAIS(Wide Area Information Server)-It is pronounced as ‘ways’,maintains separate indexes of the contents of selected documents.You can choose any index and provide WAIS with the Keywords you are looking for.

29.MOSAIC-is a program for cruising the Internet.It has a simple windows interface ,which creates useful hypertext links that automatically performs menu bar and button functions.

NETWORK

1. NETWORK-is an interconnected connection of autonomous computers.Two computers are said to be interconnected if they are capable of exchanging information.It allows computers to share computer equipment and programs. Need for networks are:

Resource Sharing: data, hardware and software resources can be shared irrespective of physical location.
Reliability: file can have two or more copies on different systems, in case if one is unavailable we can use the other.
Reduced costs: sharing of resources, reduces cost.
Fast communication: exchange information fast.

2. NODES(Work station)-The different terminals which are attached to the network and share the resources of the network are called nodes.When we attach a computer with the n/w it becomes the workstation of that n/w.

3. SERVER:-To designate a particular node,which is at a well known and fixed address,to provide a service to the n/w as a whole.The node providing the service is known as the server. A computer that facilitates the sharing of data, software and hardware resources on a network, is called server. It can be of two types.

Non-dedicated server: It is a workstation on a small network that can also act as a server.

Dedicated server: On bigger networks, a computer is reserved for the cause of serving which is called a dedicated server.

4.NETWORK INTERFACE UNIT:-The interpreter, which helps in the communication between the server and different nodes,is called NIU. The NIU is also called TAP(Terminal Access Point) or NIC (Network Interface Card).

The NIC manufacturer assigns a unique physical address to each NIC card

5.TYPES OF N/W(WAN-wide area n/w,MAN-metropolitan area n/w,LAN-local area n/w).

6. COMMUNICATION CHANNELS:-connect two or more workstations by using cables.The connecting cables between the different workstations.

(a). Twisted Pair Cable:- As a Voice Grade Medium(VGM),it is the basis for most internal offices telephone wiring.It consists of two identical wires in the pair have the same impedance to ground,making it a balanced medium.

Main advantage of this medium is it is capable of carrying a signal over long distances without the use repeaters.It is perfectly adequate medium for low speed (upto 10 mbps)applications where the distance between nodes is small.

Advantages-simple,easy to install and maintain,physically flexible,easily connected and inexpensive.

Disadvantages-Incapable of carrying signals over long distances,low bandwidth.It supports data rate 1MBPS to 10 MBPS.

(b). COAXIAL CABLE:-consists of a solid wire core surrounded by one or more foil or wire shields,each separated by some kind of plastic insulator.

Advantages-data transmission is better than twisted pair cables,can be used as basis for a shared cable n/w,can be used for broadband transmission ,and offers higher bandwidths upto 400 MBPS.

Disadvantages-Expensive compared to twisted pair cables.It is not compatible with twisted pair cables.

(c). OPTICAL FIBRES:-consists of thin strands of glass or glass like material which are also constructed so that they can carry light from a source at one end to detector at the other end.The light source used are either Light Emitting Diodes(LEDs) or Laser Diodes(LDs).

Advantages-It is immune to electrical and magnetic interference,highly suitable for harsh industrial environment.It has got a very high transmission capacity.

Disadvantages-Installation problem.These are quite fragile and needs special care.connecting the fibres together or a light source to a fibre is a difficult process. They are the most expensive of all the cables.

(d). MICRO-WAVE:-signals are used to transmit data without the use of cables.It is similar to radio and television signals and are used for long distance communication.Transmission consists of a transmitter,reciever and the atmosphere.

Advantages-cheaper than digging tenches for laying cables.It offers ease of communication over difficult terrian as well as over oceans.

Disadvantages-It is an insecure communication.The microwave propagation is susceptable to weather effects like rains,stroms etc.Bandwidth allocation is extremely limited.

(e). RADIO-WAVE:-Transmission making use of radio frequencies.Any radio setup has two parts:the Transmitter and the Reciever.

Advantages-offers mobility.It proves cheaper than digging trenches for laying cables.It offers ease of communication over difficult terrain.

Disadvantages-Insecure communication.Radio wave propagation is susceptable to weather effects like rains,thunder stroms etc.

(f) SATELLITE:-The frequency is higher than 3GHz.The earth station consists of a satellite dish that functions as an antenna and communication equipment to transmit and receive data from satellites.

Advantages-Area coverage is quite large.It proves cheaper than digging trenches for laying cables.The heavy usage of intercontinental traffic makes the satellite commercialy attractive,it can cover large area.

Disadvantages-High investment cost.High atmospheric loses above 30 Ghz limit carrier frequencies.

COMMUNICATION PROTOCOLS

PROTOCOL-is a formal description of message formats and the rules that two or more machines must follow to exdchange those messages.

HTTP(Hyper Text Transfer Protocol)-is an application level protocol with the lightness and speed necessary for distributed, collaborative, hypermedia information systems. It is a generic, stateless, object oriented protocol which can be used for many tasks such as name servers and distributed object management systems through extension of its request methods.
FTP(File Transfer Protocol):-Files of any type can be transferred, although you may have to specify whether the file is an ASCII or Binary file.It is a potent and popular way to share information over the internet.
TCP/IP(Transmission Control Protocol/Internet Protocol):-It is a layered set of protocols.TCP is responsible for making sure that the commands gets through to the other end.It keeps tracks of what is sent and retransmits anything that did not get through .TCP will split information into several datagrams,which make sure that they all arrive correctly.DATAGRAM is a collection of data that is sent as a single message.

TCP:-

Breaks data into packets that the internet can handle.
Verifies that all the packets arrive at their destination.
Reassemble the data.

IP:-

envelops and addresses the data.
enables the n/w to read the envelope and forward.
defines how much data can fit in a single envelop.

4.SLIP(Serial Line Internet Protocol):-that allows a computer to use the internet protocol with a standard voice-grade telephone line and high speed modem. More recent versions of SLIP do some TCP and IP header compression.

5. PPP(Point to Point Protocol):-allows a computer to use TCp/IP protocols and to be connected directly to the net using a standard voice telephone line and gigh speed modem.In India VSNL uses the PPP protocol. It handles error detection,supports multiple protocols,allows IP addresses to be negotiated at connection time.

6. SMTP(Simple Mail Transfer Protocol)-It is a simple ASCII protocol. This protocol ( set of rules ) enables electronic mail to move smoothly through the internet.Because of SMTP, a UNIX machine can send mail to a PC or Macintosh computer.

7. POP(Post Office Protocol):-is used to retrieve E-mail from a mail server .Using SMTP the outgoing mail is transported or routed over the internet till it reaches its destination-the host computer on which the recipient has a mail box.

8. IMAP(Internet Mail Access Protocol):- designed to help the user who uses multiple computers,perhaps a workstation in the office ,a PC at home and a Laptop on the road.

QUESTION-ANSWERS

1Q.Write down the advtgs and disadvtgs of Synchronous transmission.

Ans-Synchronous Transmission- Since fewer bits are needed to identify the beginning and end of character coding,the transmission speed is high.Main disadvantage is inaccuracy,when a reciever goes out of synchronization ,losing track of where individual characters begin and end,correction of error takes additional time.

2 Q. Differentiate between digital and analog transmission.

Ans:-The digital signal is a sequence of Voltage pulses represented in binary form.In digital technology a binary symbol is known as a binit(binary digit).The information carried by a binit is ,in most practical situation,equal to a unit of information known as a bit.In analog signal the transmitted power varies over a continuous range as in sound light or radio waves.Analog transmission is most commonly used to transmit electrical voltages representing variations in sound level (e.g. telephone system).

3 Q.What are the basic concepts of data transmission?

Ans-1.Sending or originating computer.

2.Data transmission device attached to sending computers(modem).

3.Transmission channel

4 Data transmission device attached to receiving computer.

5.Receiving computer.

4Q.What is the unit of measuring speed of data transmission?

Ans-BAUD

5Q. What are the different sections of optical fibres?

Ans- Core,Cladding and Jacket.

6Q.Define Telnet-Telnet is an internet facility that facilitates remote login.It establishes connections between 2 computers using internet.

7.Name any four IP which are provided by HTTP

Ans-FTP,MNTP,NNTP and Gopher.

TYPES of N/W:-

1.LAN(Local Area Network)-Total area is not more than 1 km.Data commu nication is at rate of 100 Mbps.It is owned by a single organization.Error rate is much lower in Lan.

2.MAN(Metropolitan Area Network)-It covers a group of nearly corporate office or a city and might be either private or public.It can support both data and voice.It has one or two cables and does not contain switching elements,which shunt packets over one of several potential output line.Not having the switch simplifies the design.

3.WAN(Wide Area Network)-covers a large geographical area with lesser cost.It helps in E-mailing.Data can be communicated to the far –flung areas with nthe help of satellites.It uses packet switching method or message switching method and uses fibre optic cables.It operates at a speed of less than 1mbps.

MODEM(Modulation /Demodulation)-converts data from digital to analog and vice versa.When we use analog facility for data communication between two digital devices we require two modems one near each digital devices.

NETWORK SWITCHING TECHNIQUES

1.CIRCUIT SWITCHING:-If two processes want to communicate a permanent physical link is established between them.This link is allocated for the duration of the communication ,and no other process can use that link during this period(even if the two processes are not actively communicating for a while.

2.MESSAGE SWITCHING-If two processes want to communicate, a temporary link is estalished for thr duration of one message transfer.Physical links are allocated dynamically.Each message is a block of data,with system information that allows the communication n/w to deliver the message to the destination correctly.

3.PACKET SWITCHING-One logical message have to divided into a no. of packets.Each packet may be sent to its destination separately ,and therefore must include a source and destination address with its data.Packets must be reassembled into messages as they arrive.

What are the differences between circuit switching and packet switching?

(a)Circuit Switching statically reserves the required bandwidth in advance,where as packet switching acquires and releases it as it is needed.

(b) Circuit switching is completely transparent while in Packet switching the carrier determines the basic parameters.

(c) The final difference is the charging algorithm.Packet switching usually base this charge on both the number of bytes carried and connect time while in Circuit switching the charge is based on the distance and time only not the traffic.

TOPOLOGIES

The pattern of interconnection of nodes in a n/w is called the topology.There are no. of factors which should be considered before choosing the topology(cost,flexibility and reliabilty.)

STAR TOPOLOGY:-consists of central node to which all other nodes are connected by a single path.

ADVTGS-

1.Failure of a single connection typically involves disconnecting one node from an otherwise fully functional n/w.

2.Centralized control/problem diagnosis

3.Simple access protocols.

DISADVGS:-

1.Long cable length

2.Difficult to expand

3.Central node dependency.

II. BUS or LINEAR TOPOLOGY:- It consists of single length of transmission medium onto which the various nodes are attached.

ADVTGS-

1.Short cable length.

2.Resilient architecture(has an inherent simplicity that make it very reliable)

3.Easy to extend.

DISADVTGS-

1.Fault diagnosis is difficult

2.Fault isolation is difficult

3.Nodes must be intelligent.

4.Repeater configuration.

II RING (Circular)TOPOLOGY:-This is also called loop.Each node is connected to two and only two neighbouring nodes.

ADVTGS-

1.Short cable length.

2.No wiring closet space required

3 Suitable for optical fibre.

DISADVTGS-

1.Node failure causes n/w failure.

Difficult to diagnose faults.
N/W reconfiguration is difficult.
Affects the access protocols.

IV TREE TOPOLOGY –is a modified form of bus topology.The shape of n/w is that of an inverted tree with a central root branching and sub-branching.

ADVTGS-

1.Easy to extend

2.Easy for fault isolation

DISADVGS-

1.dependent on the root

2.It suffers from reliability problem .

V . GRAPH TOPOLOGY-nodes are connected together in an arbitrary method. By this connection few of node may or may not be connected properly.

VI . MESH is a n/w of more than one connections for a particular node .Each node is connected to more than one node to provide an alternative route. It is an extension to p-p n/w. It provides an excellent performance for long distance networking as it provides extensive backup.Communication between two nodes can be done either directly or by any other possible route .This topology is used in large internetworking environment with stars,rings and buses attached to each node.

VII STAR –RING TOPOLGY –This configuration consists of a no. of concentration points connected together in a ring.These concentration points would in practice consists of wiring closets location on each floor of the building.These kind of n/ws are also known as HYBRID n/w as it is made up of two or more different n/w architecture.It can incorporate structures like bus,ring,star in one single n/w.

MEDIA ACCESS CONTROL(MAC) PROTOCOL

1.CARRIER SENSE MULTIPLE ACCESS/COLLISION DETECTION(CSMA/CD):-The station first listens in to what happening on the media.If there is no activity,a station is permitted to transmit.If there is a collision then one station becomes silent and trees to transmit after a random delay.Ehernet LANS use this protocol .The underlined principle is Listen,Transmit,Listen for collision,OK Listen and if collision-then start again.

2.Token Passing Ring :-is the second more widely used protocol for LAN n/ws.Aspecial signal known as Token that controls the access to the n/w.As the token is passed through the ring,the node that takes the possession of the token,gets an exclusive access to the n/w for data transmission since this protocol is based on ring topology,the token is passed around the logical ring in the assigned order,a station wanting to transmit must wait detects a token passing by.

DIFFERENCE BETWEEN CSMA/CD & TOKEN PASSING

CSMA/CD | TOKEN PASSING

1)Traffic cannot be regulated . | 1)Traffic can be regulated.

2)Nodes get the access on first | 2)Nodes are given equal priority.

come first served basis. |

3)The size and no. of data packets | 3)It can be controlled .

cannot be controlled. |

4) A station cannot determine at |4)Each gets an equal time of access.

which time it should transmit |

and which time it should not.

BACKBONE NETWORKING:- is a n/w that is used to act as a backbone for connecting different types of LANs together to form a WAN.It is a collection of high-speed transmission media used to transfer information between the major n/ws. An FDDI(Fiber Distributed Data Interface) ring is backbone n/w.

REPEATER:- is a device that strengthens or amplifies and then retransmits a signal being transmitted on a n/w. Repeater are of two types.

1. AMPLIFIER:- simply amplifies the signals as well as the concurrent noise and transmits again on the cable.

2. A SIGNAL REPEATER:-not only amplifies signal ,but also regenerates a signal by filtering out any interference or distortion before the signal is amplified and retransmitted.

HUB- It is a hardware device used to connect several computers together. They are multi slot concentrators into which a number of multi-port cards can be plugged to provide additional access as the network grows in size. Hubs are of two types:

Active Hubs- It amplifies signal.

Passive Hubs- It allows the signal to pass from one computer to another without any change.

Switch: It is responsible for filtering i.e. transforming data in a specific way and for forwarding packets of message being transmitted, between LAN segments. It is a device used to segment networks into different subnetworks called subnets.

BRIDGE-Bridge is a device that is used to link or connect two networks together i.e. a smaller no. of individual n/ws with same standard but different type of cables to make them work together as one large n/w. Bridges are smart enough to know which computers are on which side of the bridge, so they only allow those messages that need to get to the other side to cross the bridge.

ROUTER:-is a device that not only can be used to link or connect a smaller individual n/ws but it can handle different protocols. Routers maintain a routing table which determines the most efficient route for a data packet to travel. It does not broadcast data frames and keeps the traffic moving even in the case of a link failure.

GATEWAY-is a device that connects dissimilar n/ws (e.g. to link Mac n/w and a PC n/w).It establishes an intelligent connection between a LAN and external n/ws with completely different structure.

DIFFERENCES BETWEEN BRIDGE & ROUTER

Bridge links two n/ws of same protocol,where as Router can handle different protocols.
Router uses logical addresse where as Bridge uses physical addresses.

80-20 rule- 80% of the traffic on a given network segment should be local and not more than 20% of the network traffic should need to move across a backbone.

DIFFERENCES BETWEEN BRIDGE & ROUTER

Bridge links two n/ws of same protocol, where as Router can handle different protocols.
Router uses logical addresses where as Bridge uses physical addresses.

When Hubs are preferred over Repeaters- Hubs are preferred over repeaters when more than two computers are to be networked. Hubs can connect multiple computers simultaneously.

When Bridges are preferred over hubs- Bridges are preferred when we do not want to broadcast data frames. Bridges can filter network traffic based on MAC addresses.

When switches are preferred over other network devices- A switch can replace multiple bridges and offers dedicated bandwidth to each LAN segment. Thus switches are preferred when we have dedicated bandwidth for each LAN segment.

FIREWALL:The system designed to prevent unauthorized access to or from a private network is called a firewall.It is a computer system that reinforces information security between two n/ws.These n/ws are referred to as an internal n/w and an outside n/w.All the information going between these two n/ws goes through FIREWALL.That makes the firewall an ideal point at which to implement filtering,monitoring and loging of sessions between one n/w and another.

It is a device or set of devices configured to permit, deny, encrypt, decrypt, or proxy all( in and out) computer traffic between different security domains based upon a set of rules and other criteria.

There are several type of firewall techniques:

Proxy Server- Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses.
Packet filter- Looks as each packet entering or leaving the network and accepts or rejects it based on user defined rules.

COOKIES- They are messages that a web server transmits to a web browser so that the web server can keep track of the user’s activity on a specific web site.

Firewall: It is a part of a computer system or network that is designed to block unauthorized access while permitting authorized communications. It is a device or set of devices configured to permit, deny, encrypt, decrypt, or proxy all( in and out) computer traffic between different security domains based upon a set of rules and other criteria.

CRACKERS- They are the malicious programmers who break into secure systems.

HACKERS- They are more interested in gaining knowledge about computer systems and possibly using this knowledge for playful pranks.

CYBER LAW- It is a generic term, which refers to all the legal and regulatory aspects of Internet and the WWW. In India the cyber laws are contained in the IT Act 2000.

Cyber crime: An unlawful act where in the computer is either a tool or a target or both. These could be the cyber crimes:

Tampering with computer source documents
Hacking
Publishing of information, which is obscene
Child Pornography
Accessing protected system
Breach of confidentiality

ETHERNET CARD- It is a LAN architecture developed by Xerox Corp in association with DEC and Intel. It uses bus or star topologies and can support data transfer rates of upto 10 Mbps. The computers have to be installed special card called as Ethernet card.

RJ-45(Registered Jack-45) It is an eight wire connector, used to connect computers on LANS especially Ethernets.

Network Security- It refers to making efforts to make sure that only legal or unauthorized users and programs gain access to network or network resources. Various methods used are:

Authorization: It determines whether the service provider has granted access to the web service to the requestor.
Authentication: It ensures that each entity involved in suing a web service, is what it actually claims to be.
Firewall: to prevent unauthorized access to or from private network.
Encrypted smart cards: A card that can generate a token that a computer system can recognise.

Wireless Communications: Data communication without the use of landlines.

Mobile Computing: Communications wherein computing device is not continuously connected to the base or central network is known as mobile computing.

Data Channel: It is the medium used to carry information or data from one point to another

Baud: It is the unit of measurement for the information carrying capacity of a communication channel.

bps(bits per second): It refers to a thousand bits transmitted per second.

Bps(Bytes per second): It refers to thousand bytes transmitted per second.

Bandwidth: It refers to the difference between the highest and lowest frequencies of a transmission channel. This term is also sometimes used to refer to the amount of information traveling through a single channel at any point of time.

Telnet: It is an internet facility that facilitates remote login. Remote login is the process of accessing a network from a remote place without actually being at the actual place of working.

EDGE(Enhanced Data rates for Global Evolution): It is a radio based high-speed mobile data standard that allows data transmission speeds of 384 kbps to be achieved when all eight timeslots are used.

WLL(Wireless in Local Loop): It is a system analogous with local telephone service that provides telephony by deploying a multiplicity of multichannel transmit/receive base stations (transceivers) that are within line-of-site of the intended customers.

GSM- Global System for Mobile communications is a technique that uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency. TDMA(Time Division Multiple Access) uses TDM(Time Division Multiplexing) and divides a radio frequency into time slots and then allocates these slots to multiple calls thereby supporting multiple, simultaneous data channels.

CDMA(Code Division Multiple Access) It does not assign a specific frequency to each user. It uses spread spectrum technique where every channel uses full available spectrum. Data is sent in small pieces over a number of discrete frequencies available for use at any time in the specified range. Each user’s signal is spread over the entire bandwidth by a unique spreading code, which is again used at the receiver end to recover the transmitted signal.

3G: It is a specification for third generation of mobile communication technology. 3G promises bandwidth of upto 384 kbps when a device is stationary.

Free Software: It means software is freely accessible, free to use, changed, improved, copied, distributed without any payments.

Four kinds of freedom

_ Freedom to run the program for any purpose

_ Freedom to redistribute copies.

_ Freedom to study how the program works

_ Freedom to improve the program and release your improvements to the public.

Open Source Software The categories of software / programs whose licenses do not impose much conditions.

Features:

1. Freedom to run and use the software

2. Modify the program

3. Redistribute copies of either original or modified program (without paying royalties to previous developers).

It can be freely used for modifications, but it does not have to be free of charge. Its source code is available.

FOSS (free and open software) Free software- no payments Open source software- for technical progress

OSS and FLOSS

_ OSS- Source code is available(open source modified and redistributed software) free of cost or with nominal charge.

_ FLOSS- (free libre and open source software) It refers to a software which is both free as well as open source software.

FSF( free software foundation)

Non-profit organization created for the purpose of supporting free software movement

GNU (NOT UNIX) (free and open source)

Objective : To create a system compatible to unix but not identical with it.

Now it offers a wide range of software, including applications apart from operating system.

OSI(open Source Initiative): It is an organization dedicated to cause of promoting open source software

W3C(World Wide Web Consortium): It is responsible for producing the software standards for world wide web.

Proprietary software (neither open nor freely available)

Its use is regulated and further distribution and modification is either forbidden or requires special permission by the supplier. Source code is not available.

Freeware

Free of cost

_ Copying and further distribution but not modification.

_ Source code is not available

_ Eg. MS IE

Shareware

_ Right to redistribute copies

_ After a certain period of time license fee should be paid.

_ Source code is not available.

_ Modifications is not possible.

Objective- to increase user’s will to pay for the software. Limits functionality after a trial period of 1-3 months.

Some Softwares

LINUX

_ Linux: - free and open source software.

Mozilla

_ Freeware

_ No source code available

_ free internet software

Apache Server

_ Apache HTTP server is an open source web server.

PYTHON is freeware open-source cross-platform interpreted scripting language that can be used for many kinds of software development.

Difference between Open Source Software and Proprietary software

The main difference between commercial support for proprietary software and commercial support for open source software is that the proprietary software is obligatory and the open source software is optional. Most proprietary software comes without the source code, you are just buying the right to use. Whereas Open source software is free to download therefore lower in cost and has ability to link to other OSS

Perceived advantages of proprietary software include:
1) Reliable, professional support and training available;
2) Packaged, comprehensive, modular formats; and
3) Regularly and easily updated.

The downside however is that it is:
1) Costly, and
2) has closed standards that hinder further development.

Open sources software has the advantage of:
1) Low cost and no license fees;
2) Open standards that facilitate integration with other systems; and
3) it is easily customizable.

The down side is:
1) Lack of professional support;
2) Evolving developer communities;
3) Lack of release co-ordination; and
4) Erratic updates. However, with such a large development and user-base, many discussion forums and help sites are available for users.

Bandwidth: It is the amount of data that can be transmitted in a fixed amount of time is known as bandwidth. It is usually expressed in bps(bits per second) or Bps(Bytes per second).

Web Scripting- the process of creating and embedding scripts in a web page is known as web scripting. Scripts are interpreted and executed by a certain program or scripting engine.

Types of Scripts

Client Side Scripting	Server Side Scripting
Script code is downloaded and executed at client end	It is executed at server end and results are sent to client –end
Response to interaction is more immediate once the program code is downloaded	Complex processes are more efficient as the program and associated resources are not downloaded to the browser
Services are secure as they do not have access to files and database	Have access to files and databases but have security considerations when sending sensitive information
Browser dependent	Browser in dependent
Affected by the processing speed of user’s computer	Affected by the processing speed of host server
e.gVBscirpt,JAVAscript	PHP(Hypertext Processor), PERL, ASP,JSP

Computer Virus: It is a malicious program that requires a host and is designed to make a system sick, just like a real virus. It replicates very fast. It moves from file to file and computer to computer by attaching themselves to files or boot records of disk and diskettes. They can also come from Internet and e-mail attachments.

Trojan Horses: It is a code hidden in a program such as a game or spreadsheet that looks safe to run but has hidden side effects(destroying, damaging or altering information in background). It does not require a host program in which to embed itself. For e.g Christmas executable when executed pops up with an animated figure of santa and in the background, extra code could be deleting files or performing

Full Forms:

:(i) FTP- File Transfer Protocol

(ii) WLL – Wireless in Local Loop

(iii) CDMA- Code Division Multiple Access

(iv) XML – Extensible or Extended Markup Language

(v)TDM- Time Division Multiplexing.

(vi) HTML- Hyper Text Markup Language

(vii) SMS- Short message Service

(viii) WWW- World Wide Web

(ix) TCP/IP- transmission Control Protocol / Internet protocol

(x) URL – Universal or Uniform Resource Locator

(xi) HTTP- Hyper Text Transfer Protocol

(xii) LAN – Local Area Network

(xiii)WAN- Wide Area Network

(xiv) MAN- Metropolitan Area Network

(xv) GSM – Global system for Mobile

Modem: Modulator/Demodulator

FM: Frequency Modulation

AM: Amplitude Modulation

NFS: Network File Server

SIM: Subscriber Identification Module

TAP: Terminal Access point

SLIP- Serial Line Internet Protocol

PPP- Point to Point Protocol

IDEA- International Data Encryption Algorithm

Gnu- Not Unix

FLOSS- Free/Libre/Open Source Software

EDGE-Enhanced Data rates for Global Evolution

FSF- free software foundation

ARPANET- Advanced Research Project Agency Network

W3C- World Wide Web Consortium

SIM card: Subscriber Identity module

MAC: Media Access Control

NIC: Network Interface Card

Spam: It refers to electronic junk mail or junk newsgroup postings. It is unsolicited mail. To avoid it one must create a filter.

India’s IT Act: It aims to provide the legal infrastructure for e-commerce in India by governing the transactions through the Internet and other electronic medium.

Source : http://pujamcsdwarka.wikispaces.com/file/view/computer+networks.doc/154593259/computer%20networks.doc

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