internet saurav

8/9/2019 Internet Saurav

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internetinternet

By SOURAV KUMAR BANERJEE


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THE OSI MODELTHE OSI MODEL

APPLICATIONAPPLICATION

PRESENTATIONPRESENTATION

SESSIONSESSIONTRANSPORTTRANSPORT

NETWORKNETWORK

DATALINKDATALINK

PHYSICALPHYSICAL


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THE OSI MODEL contdTHE OSI MODEL contd

Physical layerPhysical layer : the physical layer is concerned with transmitting raw bits over a: the physical layer is concerned with transmitting raw bits over acommunication channel.the design issues have to do with making sure that whencommunication channel.the design issues have to do with making sure that whenone side sends a 1 bit,it is received by the other side as a 1 bit,not as a 0 bit.one side sends a 1 bit,it is received by the other side as a 1 bit,not as a 0 bit.

Data link layerData link layer :: the main task of this layer is to transform a raw transmissionthe main task of this layer is to transform a raw transmission

facility into a line that appears free of undetected transmission errors to thefacility into a line that appears free of undetected transmission errors to thenetwork layer.it does the work by converting input data to frame.network layer.it does the work by converting input data to frame.

Network layerNetwork layer :: this layer control the operation of subnet.A key design issue isthis layer control the operation of subnet.A key design issue isdetermining how packets are routed from source to destination.determining how packets are routed from source to destination.

Transport layerTransport layer :: this layer determines what type of service to provide to thethis layer determines what type of service to provide to thesession layer and ultimately to the users of the network.session layer and ultimately to the users of the network.


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THE OSI MODEL contdTHE OSI MODEL contd

Session layerSession layer: this layer allows uses on different machines to establish sessions: this layer allows uses on different machines to establish sessions

between them.sessions offer various services including dialog control,tokenbetween them.sessions offer various services including dialog control,token

management and synchronization.management and synchronization.

Presentation layerPresentation layer: this layer is concerned with the syntax and semantics of the: this layer is concerned with the syntax and semantics of theinformation transmitted.information transmitted.

Application layerApplication layer: this layer contains a variety of protocols that are commonly: this layer contains a variety of protocols that are commonly

needed by users.one widely used application protocol isneeded by users.one widely used application protocol is HTTPHTTP(hyper text transfer(hyper text transfer

protocol),which is the basis for the world wide web.protocol),which is the basis for the world wide web.

when a browser wants a web page ,it sends the name of the page it wants to thewhen a browser wants a web page ,it sends the name of the page it wants to theserver usingserver using HTTPHTTP.the server then sends the page back..the server then sends the page back.


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THE OSI MODELTHE OSI MODEL



SESSIONSESSION

TRANSPORTTRANSPORT

NETWORKNETWORK

DATALINKDATALINK

PHYSICALPHYSICAL



SESSIONSESSION

TRANSPORTTRANSPORT

NETWORKNETWORK

DATALINKDATALINK

PHYSICALPHYSICAL

HOST A HOST B


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THE TCP/IP REFERENCE MODELTHE TCP/IP REFERENCE MODEL

THEABILITYTOCONNECTTHEABILITYTOCONNECT

MULTIPLENETWORKSINAMULTIPLENETWORKSINA

SEAMLESSWAYWASONESEAMLESSWAYWASONEOFTHE MAJORDESIGNOFTHE MAJORDESIGN

GOALSFROM THE VERYGOALSFROM THE VERY

BEGINNING.THUSTHENEWBEGINNING.THUSTHENEW

ARCHITECTURETCP/IPARCHITECTURETCP/IP

CAMEINTOPICTUREWITHCAMEINTOPICTUREWITHSOMENEWPROTOCOLS.SOMENEWPROTOCOLS.


TRANSPORTTRANSPORT

INTERNETINTERNET

HOSTHOST TOTO--NETWORKNETWORK


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Internet Protocol: IP AddressesInternet Protocol: IP Addresses

Every machine on the Internet has a unique identifying number, called anEvery machine on the Internet has a unique identifying number, called an IPIPAddressAddress. The IP stands for. The IP stands for Internet ProtocolInternet Protocol, which is the language that computers, which is the language that computersuse to communicate over the Internet.use to communicate over the Internet.

A typical IP address looks like this:A typical IP address looks like this: 216.27.61.137216.27.61.137

To make it easier for us humans to remember, IP addresses are normallyTo make it easier for us humans to remember, IP addresses are normallyexpressed in decimal format as aexpressed in decimal format as a dotted decimal numberdotted decimal numberlike the one above. Butlike the one above. Butcomputers communicate incomputers communicate in binarybinary form. The same IP address in binary:form. The same IP address in binary:

11011000.00011011.00111101.1000100111011000.00011011.00111101.10001001

The four numbers in an IP address are calledThe four numbers in an IP address are called octetsoctets, because they each have eight, because they each have eightpositions when viewed in binary form. If we add all the positions together, we getpositions when viewed in binary form. If we add all the positions together, we get32, which is why IP addresses are considered 3232, which is why IP addresses are considered 32--bit numbers. Since each of thebit numbers. Since each of theeight positions can have two different states (1 or zero), the total number ofeight positions can have two different states (1 or zero), the total number ofpossible combinations per octet is 28 or 256. So each octet can contain any valuepossible combinations per octet is 28 or 256. So each octet can contain any valuebetweenbetween zerozero andand 255255..


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IP ADDRESSESIP ADDRESSES contdcontdOut of the almostOut of the almost 4.3 billion4.3 billion possible combinations, certain values are restrictedpossible combinations, certain values are restrictedfrom use as typical IP addresses. For example, the IP addressfrom use as typical IP addresses. For example, the IP address 0.0.0.00.0.0.0 is reserved foris reserved forthethe default networkdefault network and the addressand the address 255.255.255.255255.255.255.255 is used foris used for broadcastsbroadcasts

The octets serve a purpose other than simply separating the numbers. They areThe octets serve a purpose other than simply separating the numbers. They areused to createused to create classesclasses ofIP addresses that can be assigned to a particularofIP addresses that can be assigned to a particularbusiness, government or other entity based on size and need. The octets are splitbusiness, government or other entity based on size and need. The octets are splitinto two sections:into two sections: NetNet andand HostHost..

The Net section always contains the first octet. It is used to identify theThe Net section always contains the first octet. It is used to identify thenetwork that a computer belongs to. Host (sometimes referred to asnetwork that a computer belongs to. Host (sometimes referred to as NodeNode))identifies the actual computer on the network. The Host section always containsidentifies the actual computer on the network. The Host section always containsthe last octet.the last octet.


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Internet Protocol: Domain Name SystemInternet Protocol: Domain Name System

When the Internet was in its infancy, it consistedWhen the Internet was in its infancy, it consistedof a small number of computers hooked together withof a small number of computers hooked together withmodems and telephone lines. We could only makemodems and telephone lines. We could only makeconnections by providing the IP address of the computerconnections by providing the IP address of the computerwe wanted to establish a link with. For example, a typicalwe wanted to establish a link with. For example, a typicalIP address might beIP address might be 216.27.22.162.216.27.22.162. This was fine whenThis was fine whenthere were only a few hosts out there, but it becamethere were only a few hosts out there, but it became

unwieldy as more and more systems came online.unwieldy as more and more systems came online.

The first solution to the problem was a simple textThe first solution to the problem was a simple textfile maintained by the Network Information Center thatfile maintained by the Network Information Center thatmapped names to IP addresses. Soon this text file becamemapped names to IP addresses. Soon this text file becameso large it was too cumbersome to manage. In 1983, theso large it was too cumbersome to manage. In 1983, theUniversity ofWisconsinUniversity ofWisconsin created thecreated the DomainName SystemDomainName System(DNS),(DNS), which maps text names to IP addresseswhich maps text names to IP addresses

automatically. This way you only need to rememberautomatically. This way you only need to rememberwww.souravforfriends.comwww.souravforfriends.com, for example, instead of, for example, instead ofsouravforfriends.com's IP addresssouravforfriends.com's IP address ..


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URL: Uniform Resource LocatorURL: Uniform Resource Locator

When we use the Web or send an eWhen we use the Web or send an e--mail message, we use a domain namemail message, we use a domain nameto do it. For example, theto do it. For example, the Uniform Resource LocatorUniform Resource Locator (URL)(URL)""http://www.souravforfriends.comhttp://www.souravforfriends.com" contains the domain name" contains the domain namesouravforfriends.com.souravforfriends.com. So does this eSo does this e--mail address:mail address:[email protected]@souravforfriends.com. Every time we use a domain name, weEvery time we use a domain name, weuse the Internet's DNS servers to translate the humanuse the Internet's DNS servers to translate the human--readable domainreadable domainname into the machinename into the machine--readable IP address.readable IP address.

TopTop--level domain names, also called firstlevel domain names, also called first--level domain names, includelevel domain names, include.COM, .ORG, .NET, .EDU.COM, .ORG, .NET, .EDU andand .GOV.GOV. Within every top. Within every top--level domain there islevel domain there isa huge list of seconda huge list of second--level domains. For example, in thelevel domains. For example, in the .COM.COM firstfirst--levelleveldomain there is:domain there is:

souravforfriendssouravforfriendsYahooYahoo

MicrosoftMicrosoft


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URL contd.URL contd.

Every name in theEvery name in the .COM.COM toptop--level domain must be unique.level domain must be unique.

The leftThe left--most word, likemost word, like wwwwww, is the host name. It specifies, is the host name. It specifies

the name of a specific machine (with a specific IP address) in athe name of a specific machine (with a specific IP address) in a

domain. A given domain can, potentially, contain millions ofdomain. A given domain can, potentially, contain millions of

host names as long as they are all unique within that domain.host names as long as they are all unique within that domain.


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POP

CORPORATE LAN

ROUTER

REGIONAL ISP BACKBONE

TELEPHONE

SYSTEM

NAPARCHITECTURE

OF INTERNET

SERVER

FARM

CLIENT


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Inside the internetInside the internet


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