OSI AND TCP-IP MODEL

WHAT IS OSI AND TCP-IP MODEL?

The OSI(OPEN SYSTEM INTERCONNECT) is a reference model and TCP(TRANSMISSION CONTROL PROTOCOL) IP(INTERNET PROTOCOL)is nothing but the set of rules or the set of standards framed by the computer industries,to communicate with different devices

WHY DO WE NEED A SET OF STANDARDS?

A few years back there are only two major vendors in the computer industry they are DIGITAL EQUIPMENT CORPORATION and IBM(INTERNATIONAL BUSINESS MACHINE) these vendors are manufacturing computer and devices but there was a problem both the manufacturer devices are not compatible with each other,so if u buy a computer from the IBM you should buy a monitor,printer and everything from IBM.                              The problem was arise in organisation,generally organisations had different departments the marketing department using DIGITAL corp computers and accounts department using IBM computers so both of the computers could not interconnect with each other

I that time ISO(INTERNATIONAL ORGANISATION FOR STANDARDS) come to the picture they thought there is common standard or model or a set of rules should need for a computer industry after that they frame OSI reference model.And TCP-IP is the strip down model of OSI-model.Then the computer industry follows the standard.

OSI AND TCP-IP MODEL

Screenshot_2017-06-15-20-59-25

The set of boxes placed in the left-side is OSI model and right-side is TCP-IP model let me Demystified separately

APPLICATION LAYER:

The Application layer is the Layer-7 approach and the application layer contact with all the Network aware applications such as E-MAIL,FACEBOOK,TUMBLER etc…. these are the application operates in the Application layer.The operations are done by using some protocols such as

PROTOCOLS USED

HTTP

FTP

IRC

SSH

DNS

We discuss about this PROTOCOLS later

PRESENTATION LAYER:

The presentation layer is the layer which coverts the Raw-data into presentable form,the presentation layer takes the Raw data from the session layer a way back and its convert it to the presentable form,for example a image data was took from the session layer then the presentation layer converts it into image file format.This is how the presentation layer works.And all the encryption services are taken care in this layer.

PROTOCOLS USED

SSL

FTP

IMAP

SSH

We discuss about this PROTOCOLS later

SESSION LAYER:

The session layer creates and maintain session,when i say that your computer working on two different applications  such as TELNET and BROWSER the session layer creates 02 sessions and maintains them if my browser terminates,the telnet session is working as it.

 PROTOCOLS USED    

VARIOUS API’S

SOCKETS

We discuss about this PROTOCOLS later

From the above three layers we discuss a little and that is enough because The Network Engineer should mainly concentrate in Layer-4 to Layer-7 because most of the Networking device will not look beyond layer-4,so the layer 1,2,3,4 is so critical let us move on tho the next layer

TRANSPORT LAYER:

The Information coming from the upper layer comes to the Transport layer and it breaks into manageable segments and each segments add their own transport header creates encapsulation.And the transport layer take one hard decision either TCP or UDP    otherwise called RELIABLE OR UNRELIABLE communication and it allocates PORT NUMBERS.when applications need Reliable communication transport layer uses TCP which is the acronym for TRANSMISSION CONTROL PROTOCOL.when the application need a unreliable communication transport layer uses UDP which is the acronym for USER DATA-GRAM PROTOCOL.                                                                                                           The Reliable communication is nothing but it sends and receives ACKNOWLEDGEMENT when the transmission and reception of packets.                                                                            The unreliable communication means it doesn’t send any ACKNOWLEDGEMENT but the transaction should be faster compare to TCP.                                                                                   After this the port-number Allocation,transport-layer Allocate port numbers,The port-number is attached with the IP-address to identify which application this information is coming from,The Transport layer creates random source port numbers and attaches port-numbers to destination port numbers.

PROTOCOLS USED

TCP

UDP

ECN

SCTP

DCCP

We discuss about this PROTOCOLS later

NETWORK LAYER:

The network layer gets a segment from the Transport-layer and it adds the Network layer header then it called as PACKET.The critical function that performed by the network-layer is IP-ADDRESSING,the IP-addressing is the logical addressing,it selects the Best path,it compares the IP-address and it confirms that the destination IP-address in the Local sub-net,we see a IP-address and Sub-net in detail on upcoming posts.

PROTOCOLS USED

IP

IP-SEC

ICMP

IGMP

We discuss about this PROTOCOLS later

DATA-LINK LAYER

The data-link layer,When the packet come from the Data-link layer,it adds the Data-link header and that information should be known as Frame,The data-link layer is responsible for MAC-address,MAC is the acronym of  MEDIA ACCESS CONTROL,which is nothing but the Hardware address,every NETWORK INTERFACE CARD in the computer should have a mac address,It is otherwise called Physical address which is Fuse in the Hardware and it cannot be change physically.

The data-link layer having the ability to check error,The various Error checking mechanisms are CRC(CYCLE REDUNDANCY CHECK),PARITY CHECK,etc…

PROTOCOLS USED

ETHERNET

PPP

SLIP

FDDI

PHYSICAL LAYER

The Physical layer is the layer where the Actual Data-transfer happens,In this layer it deals with wires,cables,ports,nic according to a Network engineer,if someone says internet is not connected then we should check this as primary,And the data should be transferred as BITS

PROTOCOLS USED

COAX

FIBRE

WIRELESS

 

Finally from the layers,The network engineer should Troubleshoot the device from the layer-1 to layer-4

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