collections in java

it cantains list,map,set..........

What is subnet Mask

subnet (short for "subnetwork") is an identifiably separate part of an organization's network. Typically, a subnet may represent all the machines at one geographic location, in one building, or on the same local area network (LAN). Having an organization's network divided into subnets allows it to be connected to the Internet with a single shared network address. Without subnets, an organization could get multiple connections to the Internet, one for each of its physically separate subnetworks, but this would require an unnecessary use of the limited number of network numbers the Internet has to assign. It would also require that Internet routing tables on gateways outside the organization would need to know about and have to manage routing that could and should be handled within an organization

List of important port number

15  Netstat 21  FTP 23  Telnet 25  SMTP 42  WINS 53  DNS 67  Bootp 68  DHCP 80  HTTP 88  Kerberos 101  HOSTNAME 110  POP3 119  NNTP 123  NTP(Network time protocol) 139  NetBIOS 161  SNMP 180  RIS 389  LDAP(Lightweight Directory Access Protocol) 443  HTTPS (HTTP over SSL/TLS) 520  RIP 79  FINGER 37  Time 3389 Terminal services 443  SSL (https) (http protocol over TLS/SSL) 220  IMAP3 3268 AD Global Catalog 3269 AD Global Catalog over SSL 500  Internet Key Exchange, IKE (IPSec) (UDP 500)

Gateways

A system that bridges two systems.


A computer connected with various computer, wants to transfer a packet, can transfer dirctly to the router by giving router address as gateway address at ip address portion.


Gateways are used to connect two dissimilar lan’s .


Gateways work in application layer of osi model.


A gateway is required to convert data packets from one protocol formate to another before forwarding it, as it connects two dissimilar networks.

IP Packet Security

IP PACKETS HAVE NO INHERENT SECURITY – NO WAY TO VERIFY,


• How to ensure that, the data has not been modified in transmit.


• How to ensure that, the data has not been viewed by the third party.


• How to ensure that, the data that you have received is from the right person (from the true sender).


• What about, Non repudiation.


Hence,


IPSec provides an automated solution for these three areas,


1. Authentication


2. Integrity


3. Confidentiality


4. Encryption


Standard IP Packet:






First, data.


The data is encapsulated/wrapped by TCP Header, which determines the destinations application on the machine your sending to .


It determines for which application data is ment for. by sending port number of the application


Example: 80 for HTTP, 21 for FTP….


IP Header is encapsulated/wrapped on TCP Header.


IP Header determines where the data should go on the physical network.


It takes care of taking data from one computer to another computer on the network/ internet.


Once the data reaches destination first IP Header is removed, then TCP Header says where the data should go with the destination system and finally when it gets to that location TCP Header is also removed, the data is reassembled and delivered to the application.


NOW THE DIFFERENCE BETWEN STANDARD IP PACKET AND IPSEC PROTECTED PACKET IS THAT,






IPSec Packet:






First, data


Data is encapsulated with TCP Header.


Then, IPSec Header is encapsulated


And now IP Header is encapsulated


IPSec is application independent because of which it enables authentication, integrity, confidentiality, encryption into the system.





How to implement IPsec enabled communication?


IPSec can be implemented through polocies that enforce a set of packet filters on inbound or outbound traffic.


Filters set to or (with the help of filters you can):


• Block


• Permit


• Negotiate security (encrypt)


IPSec policies used to:


• Protect contents of IP packet.


• Defends against network hacks.






1.


IPSec can be enabled through “IP Sec policy editing tool” -


• open this editing tool via “mmc”


• Go to run > type “mmc”> file>add/remove snap in > Add > select “IPSec policy management” and click “Add”> local computer > finish > ok.


• And you can now see three policies at the right side of the window “client (respond only)”, “server(request security)”, “secure server(require security)”.


• To implement any of the policy , right click policy and click on ” Assign “.The policy will be enabled.


To implement IPSec policies on active directory users or on organizational unit.


• Right click organizational unit>properties>Group policy> ” new ” give a name and ” edit ” >


• computer management > windows > security settings > IP Security policy on active directory and you will see three preloaded filters/policies.


• You can assign or unassign any policy.






Configuring IPSec policies


Default policies:


1. Client (Respond only):System won’t use IPSec unless requested.


2. Server (Request security):Try to initiate IPSec communication whenever possible.


3. Secure Server(Require Security):Disallow any communication that does not use IPSec.


4. Can only assign one policy at a time.










2.


IPSec works under IP Layer of TCP/IP model.


Type ” secpol.msc ” in run to open IP Security policy console.


Need to set rules (must be defined) : what type of packets must be blocked or encrypt or filtered or.. when packets communicate from ipaddress 192.168.1.1 192.168.1.10


Policy Rules


• Tell IP sec how to behave(encrypt certain communication, sign other communication, etc.)


• A rule is defined by the combination of IPSec actions + IPSec Filters


• Filter: only activate the rule if traffic comes from ip address 192.168.2.23 and uses FTP.


• Action: encrypt the traffic






Go to IP security management on local computer > right click ” Manage IP Filter list and filter actions “ > under “ manage filter actions ” > click ” Add ” > welcome screen > next > give name as ” block ” and next> select ” block” and next> “finish” > Now go to the Assigned policy > properties > under rules, double click on ” ALL ICMP Traffic ” > under filter action , select ” Block ” > ” Apply ” and ” Ok “.


the above rules is If the filter match’s icmp traffic or ping traffic the action is to block the traffic.














3.


Above is for default policies and if we want to set our own policy rule , example


when ever system 23 communicate with system 100 vice-cersa their communication must be encrypted(secure).






IPSec policy Example:


Two systems: 192.168.2.23 and .100


Filter: Triger rule when traffic to .23, over any port.


Action : Encrypt data.


Authentication: preshared key – bosco


Create filters and actions, then build the rules into the policies at both the machines.






Steps:


1. start > run > secpol.msc >


2. First, we are going to create a new filter,


3. Rightclick on IP Security policies on local computer > Manage IP Filter lists and filter actions, > under Manage IP Filters click ” Add ” > Add > source address: My ip address, Destination address: a specific ip address:192.168.2.23 , ok > under protocol, select ANY>under description, traffic to 23 and click on ok > ok >


4. Then , we need to create an action,


5. Under Manage filter actions, click ” Add ” > Select ” Negotiate Security “ , click on ” Add ” and select ” Integrity and encryption ” (data will be encrypted and verified as authentic and unmodified). > ok > ok > close.


6. Now we need to create a new ip security policy that will use a rule that will assemble both filter and action that we just created(defined).


7. Right click on ” IP Security policies on local computers ” > select ” create IP Security policy ” > a welcome wizard opens, click next > Name: traffic to computer 23, next > uncheck ” activate default response rule “, next > finish


8. A dialog box containing rules & general will open immidiately.Notic that: the ip filter list(dynamic) is unchecked because we said that we created a policy rule. so here you need to attach filter and action you have created. to do this ,


9. click on ” Add ” > under ip filter list, select the ip filter u created and go to > Filter Action, select new filter action u created for encryption. and go to > Authentication method (authentication methods specify how trust is establised between the computers. These authentication methods are offered and accepted when negotiating security with another computer) , click ” edit ” > select use this string(preshared) :type ” bosco “ and click ” OK ” > “apply” , ”Ok” > “Ok” > “OK”.


10. This new Policy is published on the right side window, Eg: traffic to computer 23


11. Right click policy ” traffic to computer 23 ” >”Assign”


12. now after assigning , I have to go to the other computer ( 192.168.2.100) and reverse the process, I have to create a rule which gonna be called traffic to .100 and configure it exactly in the same way that you did here at 192.168.2.23 using same preshared key.


13. Test by pinging 192,168.2.23 and .100 at each other computer.






This is how you can configure your computers to exchange a secure communication within and between computers.

What is switch?

A switch is a device which connects various systems in a network.


Switch maintains MAC address table.


Packets are directly transferred to the destination without broadcasting.


Switch is considered as an intelligent device.


In switch , each packet gets th same speed.


A switch is Full-duplex (can forward & receive simultanously)


Packets are filtered by switches.


No concept of collision domain or No collision as it is full duplex.


Works in “Data link layer” layer 2 and in layer 3






There are two types of switches,


1.Managable switch – has console port,we can make configuration


2.Unmanagable switch – has no console port.






Cisco divided switches in 3 layers:


1.Access layer switches : It works in layer 2 as it understands MAC address only.It doesn’t understand IP address.Switches series – 1900 & 2900


2.Distribution layer and 3.Core layer switches: It works in layer 3 because it understands MAC address as well as IP address. Switches series – 7000 & 10000.


Distribution layer and core layer switches can access millions of packets per second - whereas - Router can access 1 lakh packets per second.

What is an IP?

IP (Internet protocol) is a method or protocol by which data is sent from one computer to another computer on the internet.


Each computer on the internet has at least one IP address that uniquely identifies it from all other computer on the internet.


When you send or receive data (for example , an e-mail or web page), the message gets divided into little chunks called packets.


Each of these packets contains both senders internet address (IP address) and the receivers address.


Any packet is sent first to gateway computer that understands a small part of internet.


The gateway computer reads the destination address and forwards the packet to an adjacent gateway that in turn read the destination address and so forth across the internet until one gateway recognizes the packet as belonging to computer within its immediate neighborhood or domain.


The gateway then forwards the packet directly to the computer whose address is specified.


Because message is divided into number of packets, each packet can, if necessary , be sent by a different route across the internet.


Packets can arrive in the different order they were sent in.


The internet protocol just delivers them(IP Packets).
It is up to other protocol, the TCP/IP to put back in the right order.

What is HUB?

A HUB is a device which connects various machines in a network.


It’s major function is to replicate data it receives from one device attached to it.


Hub is "Signal Splitter"


Operates in "Physical Layer"


“Collisions” will occur in hub and it listen for collision domains.


Hub is “Half-duplex“(can receive or forward only)


Also known as ” Concentrator”


Types,


Passive (splitter)


Active (signal boosting)


Intelligent (manageable)

Ethernet

Originally developed by xerox corporation, that can link upto 1024 nodes in bus network.


A networking hardware , communication and cabling standard.


A high-speed standard using a base band (single channel) communication technique.


Ethernet Provides row data trnafer rate of 10 Mbps.


Ethernet uses (CSMA/CD) to prevent network failures when two devices try to access the network at the same time.

What is repeater?

Repeater is a device used to extend a network.


Extends the range of a network.


Amplifies or regenerates the data signal, in order to extend network.


Doestn’t amplify noise.


A repeater amplifies and cleans up digital signals and forwards their destination.

What is MAC address?

MAC (media access control ) 48-bit number (6-byte).Unique to each and every Lan card , represented in hexadecimal notation.

MAC address is physical address of a network adaptor. It is permenant address of network adaptor.


This address is used for communication at low level.


This address comes from manufacturer.


Securities are based on MAC address.

NIC (network interface card)

 Also known as Lan card ,Ethernet card, Network/Ethernet adaptor.




 It is an interface between computer and network cables.


It is a mediator between system and network


 Functions of LAN card are,


 *Data transfer


 *Buffering data construction


 *Medium access control


 *Encoding and decoding


 *Data transmission and reception


 Lan cards are full duplex ( they can send and receive data )


 Lan card can have UTP, BNC, AUI ports.


 Lan card puts packet on the cable.



 It contains MAC address.

Different Types of Topologies

* Star topology


* Bus topology


* Ring topology


* Token ring topology


* Hybrid topology


* Mesh topology


Topology means Structure of computer network or Design of computer network.






Star topology:


In star topology all the systems are connected to a central device which may be hub or switch.


Advantage: If one computer cable is broken or damage then other computers will not be affected i.e Network is not affected.


Diadvantage: If central device (hub or switch) stops working then whole company network is blocked (any system can’t communicate with each other).




Bus Topology:


In bus topology all the systems are connected to a single cable/channel or back bone .Computers are connected with this cable using BNC connector or T connector.At the both ends of cable Terminators are connected.


Advantage: Cheap and Easy to implement.


Disadvantage:If terminators are not connected or open then data will bounce back.






Ring Topology:


In ring topology each computer is connected to each other .ie every system is connected to their next system in form of ring .


Advantage: Easy to install and easy to troubleshoot.


Disadvantage: If one of the computer goes down or if one of the cable break between two machines then whole the network is down.Data packets can’t go further.




Token Ring Topology:


In token ring toplogy, all the systems are connected to a central device ”MSAU” multiple station access unit Hub.



Token ring is 802.5 standard.


Developed by IBM


Has a unique token passing access method.


Contains an “electronic signal” which constantly rotates in MSAU hub.


Here if one computer needs to send a packet to other then this packet from source machine is taken or attached to token(electronic signal) and forwarded or takes to the destination address machine.


Disadvantage: If this central device (MSAU) stops working or fails then whole the company network is down or all the systems connected can’t communicate with each other.




Hybrid Topology:


Mesh Topology:

What are the advantages of having computer network?

1.Increased communication capabilities.


2.File sharing: Network offer quick and easy way to share files directly at a rapid speed thus saving time and integrity of files.


3.Resouce sharing : All computers in a network can share resources like printer, scanner, modem, fax machines, hard disk.


4. Security: Specific directories can be password protected to limit access to authorized users. Also, files and programs on a network can be designated as "copy inhibit" so you don’t have to worry about the illegal copying of programs.


5. It is also possible to share data files across the network by creating a share on the hard drive and allowing other people access to that information.


6.Increases the productivity.


7. You can connect all the computers which are connected through a network to the internet by using a single line. So it means that you can save the connection cost for each computer but you internet connection must be fast.


8. Internet connection sharing - Using a home network, multiple family members can access the Internet simultaneously without having to pay an ISP for multiple accounts. You will notice the Internet connection slows down when several people share it, but broadband Internet can handle the extra load with little trouble. Sharing dial-up Internet connections works, too.


or


Connect your entire office to the Internet through one line.

By having a client -server network, we can
1. Centralization : Data and security can be controlled from the centralized server .
2.Scalability : New elements can be upgraded into the system very easily.
3. Flexibility : New technology can be integrated into the system easily
4. Availability : Server, data, resources can be easily accessable from any remote location easily.
5.Interoperability : Server, client, network work with each other.

What are the types of transmission media ?

Signals are usually transmitted over some transmission media that are broadly classified in to two categories.


Guided Media:


These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.


Unguided Media:


This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.




Two types of wires/cables are used here,



1.Mostly ” straight thru cable”/Straight cable (cat5e)


It is 8-wire arranged in 4 pairs.


It is UTP (unshielded twisted pair)


2. Cross cable


Practical Requirments for arranging wire:


* Crimping tool – for crimping wire


* RJ 45 connector – 8 pin


* Cat5 cable






Arrangement of wire in RJ45 connector is based on colour combination


For Straight thru cable:Order from 1 to 8 pins


1. orange-white


2. orange


3. green-white


4. blue


5. blue-white


6. green


7. brown-white


8. brown

History of computer network

 In 1969,a network called ARPANET (advanced research project agency) was created. For transmission lines of 56kb dedicated line.


 In 1970, DECNET (digital electronic corporation network) was created . For proper trait design.


 In 1977-83, ETHERNET was created . Network capacity10Mhz. Support token ring topology.


 In 1981, a network called TCP/IP (transmission control protocol/internet protocol) was created. To support LAN and WAN. Which lead to the beginning of INTERNET.


 In 1980’s , GIGA BYTE network was created. To support applications such as FTP, SMTP, HTTP, POP3, IMAP4.

What is memory chip?

Memory chips are also known as RAM (random access memory ) chips.



Represents primary storage


They hold data before processing and information after processing ,before it is sent along to an output or storage device.

What is hardware of computer?

Physical part of the computer like mouse, monitor, keyboard, CPU etc


The electronic , magnetic, mechanical devices of a computer are known as hardware.

What is mother board?

Also know as “system board”.
Mother is main circuit board in computer.


This is a board to which every thing else-such as keyboard , mouse, printer-attaches through connectors (called ports) in the back of computer.


The processor chip and memory chip are also installed on the motherboard.


It has extension slots for expanding the pc’s capabilities –which give you places to plug in additional circuit boards , such as for video , sound, communications (modem)

What is chip and why it is important?

A chip is a tiny piece of silicon that contains millions of miniature electronic circuits used to process data.



Chips have made possible the development of small computer.

What is internet?

Mother of all networks .


Internet is a world wide network that connects hundreds of thousands of smaller networks .


Internet connects large geographical areas like WAN (wide area network) or network of networks.

What are the different types of computer networks?

PAN( personal area network) : Network that is meant for one person


Eg: A wireless network connecting a computer with it’s mouse, keyboard, printer is PAN. Covers 1m distance only.



LAN (local area network) : LAN’s are privately owned network which covers a room, building or a campus ( 10m, 100m, 1km) of distance.


LAN’s are widely used in offices, companies, industries.


Characteristics:


* Lan’s are restricted in size


*Lan’s uses transmission media as cable , to which all the machine are attached.


*Lan’s basically uses Bus and Ring Topologies( network structure) to broadcast.


Traditional Lan’s runs at the speed of 100Mbps and newer Lan’s runs at the speed of 10Gbps.


Lan’s are un-switched ( they don’t have routers).




MAN (metropoliterian area network): MAN covers city ( about 10Km) in distance.


The best example of Man is the CABLE TV NETWORK available .


Cable TV is not the only MAN ,development in high speed wireless internet access resulted in MAN.


MAN’s are also un-switched ( i.e don’t have routers).




WAN (wide area network): A wide area network covers a large geographical areas like country or a continent ( about 100Km, 1000Km, 10,000Km)in distance.


In WAN, subnet consist of two components Transmission lines like copper cable, optical fiber ( move bits between machines) and Switching elements or routers (specialized computers or devices that connects 3 or more transmission lines, when date arrives to incoming line, router choose an outgoing line on which to forward them.


Hosts ( user’s computers) are connected to subnet.


Subnet is owned and operated by telephone company or isp.


The subnet is collection of communication lines and routers ( but not hosts).


The job of subnet is to carry message from host to host .


In most WAN’s , the network contains numerous transmission lines , each one connecting pair of router. If two routers do not share a transmission line , wish to communicate they must do this indirectly via other router .


When a packet is sent from one router to another via one or more intermediate routers, the packet is received at each intermediate router in its entirety , stored until the required output is free, and then forwarded.


This principle is known as “store and forward or packet switched subnet”.

What is www (world wide web)?

An interconnected systems of computers all over the world that store information in multimedia form.


Multimedia: “from multiple media” , A technology that presents information in more than one medium, such as text, still images, moving images, sounds ,animations.

What are the three directions in which computer developed?

The three directions of computer development are:


1.Miniaturization


2.Speed


3.Affordability




Miniaturization deals with minimization of computers.( Smaller than normal)
The miniaturixed processor or microprocessor, in personal desktop today can perform calculations that once required a computer filling an entire room.


Speed = Because of miniaturization, more between components are introduced into computer, providing faster processing speeds and more data storage capacity.


Affordability = Todays microprocessors are affordable when compared to the cost of processors 15 years ago.




The development of computer generations was due to invention of an electronic device


At 1st Generation computer:


ENIAC (electronic numerical integrated and calculator)


Used VACCUM TUBES (an electronic device) to store data in it. Drobage – large, expensive, difficult to maintain , more power consumption


At 2nd Generation computer:


Computer entered into 2nd generation with an invention of electronic device-transistors.


Several vaccum tubes were able to accommodate in small, fast, reliable, transistor


A transistor is a small device used as a gateway to transfer electrical signals along predetermined paths (circuits).


At 3rd Generation computer:


The development of 3rd generation of computer was due to another electronic device –tiny integrated circuits (IC’s).


Again, several transistors were accommodated in tiny integrated circuit (IC).


IC’s are entire collection of electrical circuits or pathways that are now etched on tiny squares (chips) of silicon half the size of your thumbnail


At 4th Generation computer:


The development of 4th generation of computers was due another electronic device –microprocessor


Again, several IC’s were accommodated in a single microprocessor chip made up of silicon.


The miniaturized processor or microprocessor in personal desktop today can perform calculations that once required a computer filling entire room.


At 5th Generation computer:


The introduction to fifth generation of computers was not due to any electronic device.


Instead, the development of fifth generation of computer was based on “HUMAN BEHAVIOR” as “ ARTIFICAL INTELLIGENCE”.

What is firewall?

* System that establish access control policies among network.


* They can block information from entry.


* A combination of hardware and software that protects a network from attack by hackers that could gain access through public network, including the internet.

What is hard disk drive and why it is important?

It is a storage device that stores billions of characters of data on a non-removable disk platters inside the computer case.



Hard disk is important because it holds much more data than diskette. Nearly all computers use hard disk as their principal secondary storage medium.

What is processor chip?

A processor chip is a tiny piece of silicon that contains millions of miniature electronic circuits (IC’s) that executes instructions to process data.


Speed is expressed in “MHz (megahertz) “, millions of processing per second or “GHz (gigahertz)”, billions of processing per second.

What is CPU (central processing unit) and why it is important?

Device consisting of electronic circuitry that executes instructions to process data.


CPU is important because it is considered as brain of computer.


CPU performs arithmetic and logical calculations and controls the operations of other part of computer.


CPU may be single silicon chip or a


series of chips .


A chip contains thousands of electronic switching circuits.


The CPU consists of ALU, REGISTERS, CONTROL UNIT, INTERNAL BUS.


ALU carries arithmetic and logical operations .


Registers store data and keep track of operations.


Control unit controls and regulates various operations.


Internal Bus connects the unit of the CPU with each other and with external components of system.

What are the basic components of a computer?

The basic component of a computer system are ,


Input


Memory unit


Control unit


ALU


Output





Input :

They convert data into electronic machine readable form (binary form ) or convert letters ,numbers into strings of binary data.


Eg : Keyboard, mouse , touch screen, optical scanner etc.






Memory unit :

Computer store data internally (in chips) and externally (on storage devices).


Internally computer store data in silicon ram chips that are mounted directly on computer main circuitry .


These ram chips contains millions of electronic switches that are sensitive to changes in electric current.


There are two types of RAM chips : static and dynamic


Static ram chip hold data as long as current flows through the circuit, Whereas dynamic ram chips need high or low voltages applied at regular intervals-every two milliseconds or so if they are not to lose their information.


Another type of internal memory consisting of silicon ROM (read only memory) chip on which all the


switches are already set.


The patterns on these ROM chips contains programs, commands, data that the computer needs to function correctly.


RAM chips are like piece of paper that can be written on, erased, and used again.


ROM chips are like a text book with it’s words already set on each paper.


Both RAM and ROM chips are linked by circuitry to the cpu.


Control unit:


Control unit controls and regulates various operations and devices of computers.




ALU (arthimatic and logic unit) :


ALU performs arithmetic operations such as addtions, substractions, multiplications etc and logical operation such as AND operation , OR operation XOR operation.




Output unit:


They convert the data that has been manipulated/processed by the processor or the cpu in human readable form.


or


The result tht is obtained by the cpu is in bibary form / electronic machine readable form and this result must be converted to human readable form , which is done by output devices.


Example: Montor,Printer etc

what are different types of network hardware?

NIC ( network interface card)


Repeater


Switch


Router


Hub


Modem


Server


Gateways


Bridges


firewall

what are different types of network hardware?

what are basic operations of computer?

There are four basic operations of a computer. They are,



1. Input : Accepting data that has been represented in a way that computer can use.


2. Processing : Performing arithmetic and logical calculations.


3. Output : Displaying result


4. Storage : Storing result for later/future re-use

why is computer important

Computer greatly speed up problem solving and other tasks, increasing user’s productivity.

Easy to create presentations.


Easy to solve complex computations


Easy to communicate and share information from one computer to other computer and users to users.


Easy to store data in a data base for long period of time provided security.

what are different types of computers

1. Super computer


2. Mainframe computer


3. Workstation computer


4. Microprocessor


5. Microcontroller



What is a super computer?


A super computer is a high capacity computer with hundreds of thousands of processors that can perform over 1 trillion calculations per second.


Super computers are used for research purposes , designing air planes, oil explorations , whether forecasting, modeling molecules, breaking codes, simulating explosion of nuclear bombs, creating film animations.


Is the fastest calculating device ever invented.


Can cost up to $85 million.


Looks like rows of refrigerator size boxes.


A supercomputer named ASCI white (accelerated strategic computing initiative white) developed by IBM


Has 8192 processors


Can process 12.3 trillion


operations per second.


Uses 83 miles of wiring.


It weighs 106 tons.


It has 97,000 times the memory of a 64-megabyte micro computer.


It has 16,000 times the secondary storage capacity of a 10-gigabyte micro computer hard disk.


It takes up to 12,000 square feet of space .




What is mainframe computer?


Mainframes are used by large organizations that need to process millions of transactions like airline, insurance companies, universities, banks.


For processing of millions of transactions.


Mainframes process millions of instructions per second.


Can cost around $5000-$200,000 and vary in size from small , to medium, to large, depending up on their use.




What are workstation computers?


Workstations are expensive, powerful computer used for complex scientific, mathematical and engineering calculations and for computer aided design and computer aided manufacturing.


Workstations are used for designing air planes fuse- lages , prescription drugs, movie special effects.


Workstations are more popular for their graphics capabilities which are used to breathe three-dimensional life into movies such as Jurassic park 3 and pearl harbor.




What are micro computers?


Also called personal computers


Cost $500-$5000


Can fit to a desk or on a desktop, can be carried around.


They are standalone machines or are connected to a computer network, eg: lan


Types of microcomputers,


Desktop pc’s


Tower pc’s


Laptops or notebooks


PDA (personal digital assistants-palmtops




What are micro controllers?


Also known as embedded computers are tiny specialized microprocessors installed in smart appliances and automobiles.


These microcontrollers enable microwave, ovens Eg: to store data about how long to cook your potatoes and at what temperature.

tcp/ip model view

There are four layers in TCP/IP model.


1. Application Layer


2. Transport Layer


3. Internet Layer


4. Network Access Layer






Application Layer (AL):


• Application Layer (AL), contains those protocols which provides services to users.


• Web browsing, e-mail, encryption, session establishment all these things happen in application Layer which uses protocols such as,


• HTTP, SMTP, DNS, TELNET, FTP, NFS, DFS, IMAP4, POP3, NNTP, SSH, SSL, GOPHER.


• Application Layer (AL), defines network application services like file transfer, network management.


• Identification of services is done using port numbers. Ports are nothing but socket i.e. entry & exit point to the layer.


• Application layer, Presentation layer, Session layer of OSI model


• Responsible for converting data into standard format ex: ASCII, JPEG, MIDI, MP3.


• Encoding-decoding, encryption-decryption, compression, NFS, RPC (remote procedure code).






Transport Layer (TL):


• Two important protocols are used in Transport layer (TL). They are TCP and UDP


• Transport layer (TL), deals with actual manipulation of data and prepares it for delivery through network.


• If data is too large for the single frame, then TL breaks it into smaller pieces and assigns sequence number.


• It ensures that all the data is received in the right order than it was sent.


• TL is responsible for ensuring data is sent and received successfully.


• TL is responsible for verifying delivery of packets.


• Identification services, sequencing, flow control, error correction, segmentation, reassembling is done here.






Internet Layer (IL):


• Internet layer (IL), deals with, finding the way to the destination.


• Internet layer (IL) defines, IP addressing, routing, switching.


• It determines where the data should go on the physical network.


• It is responsible for routing each packet to its destination.


• Defines network address.


• Protocols that are used in this layer are routing protocol-OSPF, RIP, IGRP, EIGRP Routed protocols-IP, IPX, Appletac. And DDP (datagram delivery protocol), ICMP, IPSec.


• This layer is also known as network layer in OSI model.


• IL provides best path to the data to reach destination.


• Device working in this layer is Router.






Network Access Layer:


• It is responsible for putting frames (packets) on the wire.


• Responsible for setting bits & bytes, electrical signals and impulses back and forth across the wire (coaxial or twisted pair).


• Deals with wire, connectors, signals, pulses, modems, fiber optic cable (in for of light).


• “Doors between worlds” connecting physical aspect of network (cables & Digital pulses).


• Describes specifications for topology.


• Devices used here are- HUB, Switch, Repeater, Bridges, and NIC.


• MAC – it talks about physical address


• LLC – it talks about wan protocols like ppp, hdlc, and frame relay.

what is computer network

A network is group of computers interconnected with each other to exchange information or resource.



A computer network is collection of interconnected autonomous computers interconnected in a single technology.


Two computers are said to interconnected with each other if they share some information between them.

what is software and what are the software types

A software is collection of programs which is used to perform a particular task.


Program: Is a list of instructions, written in a programming language that tell computer how to perform operations in order to accomplish a task.


or


Computer process data under control set of instructions called computer programs


or


List of instructions that tells computer what to do.


There are two types of software’s ,


Application software


System software


Application software: Software that allows to write documents, do spreadsheets etc


Enables you to perform specific task- perform work, solve problems etc


Eg: word processing, spreadsheets, database manager, graphics, communications packages.


System software: Helps computer perform essential operating system tasks and enables the application software to run.


System software consists of several programs .

The most important is operating system the master control program that runs the computer.


System software is very important because application software cannot run without system software.

what is ip address

An IP address is an address with which a computer is identified on a network (internet).


An IP address is a logical address of the network adaptor.


An IP address is a 32-bit number which has two parts network number and host number.


00001010000001110000010100000001


Computer won’t have problem in understanding this number but we as human can’t deal with binary.


An organization named IANA (internationally assigned numbering authority) as divided this 32-bit number into 4-octat and has given the range from 0-255


00001010- 00000111- 00000101- 00000001


An IP address in represented in decimal notation form like,


192.168.1.1


Based on the range from 0-255 IANA has divided this 32-bit number into three classes,


 Class A from 0-126


 Class B from 128-191


 Class C from 192-223


 *127 is loopback address


 *224-255 is for research and development purpose.


To manage and maintain network again IANA has divided each class of IP address into 2 parts,


 *Network portion (N/P) –represented by 1’s


 *Host portion (H/P)- by 0’s


IANA has assigned class A with single octet (8-bits) for network portion and three octet (24-bits) for host portion.
DSM (default subnet mask) : 255.0.0.0


IANA has assigned class B with two octet (16-bits) for network portion and two octets (16-bits) for host portion.
DSM (default subnet mask) : 255.255.0.0


IANA has assigned class C with three octet (24-bits) for network portion and single octet (8-bits) for host portion.
DSM (default subnet mask) : 255.255.255.0

A subnet mask defines network portion of ip address and host portion of ip address.By knowing the subnet mask information, we can easily identify a particular machine ip belongs to which class.


IP Address is dividedinto two types:
1. Private IP Address.
2. Public IP Address.

Private ip address are basically used within the LAN environment.All private ip address are free to use you don't have to pay to any one for using these address.It is also known as Free IP Address.

Private IP Address range:

Class A = 10.0.0.0 - 10.255.255.255
Class B = 172.16.0.0 - 172.31.255.255
Class C = 192.168.0.0 - 192.168.255.255

Public IP Address:
Public ip address are used in WAN environment.Used for connection to internet.Public ip address are not free , you need to pay for ip address (to isp or iana).
A part from above private ip address range from each and every class all the ip's are public ip's.

what is tcp/ip model

1. TCP/IP is a protocol stack or protocol suite or group of related protocols, each working together with in a prescribed standard.


2. TCP/IP is the most popular model or a standard used for the connections to the internet.


3. TCP/IP is set of rules/protocols for communication on internet.


4. TCP/IP is the communication protocol for communication between computers connected to the internet.


5. TCP/IP software is built in all the major operating systems, such as windows, unix, mac o.s. The purpose of TCP/IP development was to allow computers to communicate over long distance networks.


6. Internet Browser and Internet Servers uses TCP/IP to connect to the internet. Your Browser uses TCP/IP to access internet servers, and servers uses TCP/IP to send HTML back to your browser.


7. The Standard defines how computers should be connected to the internet , and how the data should be transmitted between them.


8. In TCP/IP, ech protocol work together, they perform specific function but they inter-relate and depend on each other within a standard.


Protocol: A protocol is an agreement between the two communicating parties on how the communication should proceed.


Protocol are rules for communications on a network.


Networking software is organized as a protocol.


A communication protocol is a description of rules computers must follow to communicate with each other.

what are disadvantage of computer network

1.Network faults can cause loss of data.


2.Network faults could lead to loss of resources.


3.Systems open to hackers.


4.Could become inefficient.


5.Could degrade to performance.


6.Resources could be located too far from users.


7.As a work group user cannot Login from other work group machine within LAN network.


8.User also cannot login from any remote machine from WAN environment.

what is router

A router is a device or a specialized computer which takes data packets from incomming lines, and decides outgoing lines on which to forward them.


A router is responsible for routing the data packets towards their destination.


A router is a device, which enables communication between two different networks or enables communication between two different series/classes of network.


A router is a internetworking device.


A router routes the packet from one logical network to other logical network.


The main job or function of router is to calculate the best path/route for the packet to reach to it’s destination. or


The main role of router is to determine the best path towards destination.


It determines where the data should go on the physical network.


It deals with, finding the way to the destination.


Types of Routers:


There are two types of routers: Fixed router and Modular router


Fixed router:


1. Parts in the router are inbuilt where modification to theinterface is not possible.


2. Access layer router are the exmple of fixed router except 1600 and 1700 series.


Modular Router:


1. Parts to the router can be added and removed i.e modification to the interface is possible.


2. Distribution and core layer router are the examples of modular router.






Cisco Routers are divided into 3 catagories or layers:


1. Access Layer Router


2. Distribution Layer Router


3. Core Layer Router


Access Layer routers are used by small organizations.Also knownas desktop or company layer routers. Router that are mostly used here are,router series – 800, 1000, 1600, 1700, 2500.

Distribution Layer router are used by ISP’s .Also known as IS layer routers.Router series – 2600, 3200, 3600, 3700.

Core layer router are used by global ISP’s .Also known as backbone routers. Router series – 6400, 7200, 7300, 7400, 7500, 7600, 10000, 12000.

where is computer used now a days

Computers are used almost at places these days,



1.Computers are used in office work for storage of data, for creating and managing database using access, for slide presentation etc.


2.Computers are used at scientific laboratories for analysis of research information.


3.Computers are used for reservation purposes at railways ,airways, cinema hall etc.


4.Computers are used at hospitals for diagnosing purpose , used in various operations like eye, heart, brain operations etc.


5.Computers are used for publication works.


6.Computers are used at educational institutions like schools , colleges ,universities for maintaining records ,database etc.


7.Computers are used in banks for money transaction purposes .

what is computer

A computer is an electronic device which accepts input from keyboard ,stores it in the memory by performing arithmetic and logical operations and displays the output on the screen.



A computer is a device which is capable of performing billions of operations and make millions of decisions per second at a marvelous speed .


Eg: A computer can perform million of additions per seconds which a human requires nearly a life time to complete the same number operations using a desk calculator .

what is modem

It is a device , which converts binary code( from the computer ) to the analog signal needed for transmitting messages over telephone lines.

It does modulation-demodulation
or
A device used to convert digital signals into analog tones that can be transmitted over the telephone network.


Types,


*Internal Modem


*External Modem
*Card Version

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