OSI Model

OSI Model :-

What is OSI model:-

·      It stands for Open System Interconnection.

·   International Standard Organisation establish a committee in 1977 to develop an architecture for computer connection.

·      It is a reference model.

·      In 1984 OSI was approved is an international standard for communication architecture.

·   The term OPEN denotes the ability to connect any two system which conforms to the reference model & associate standard.

·      It consist 7 layer.

·      Each layer has a different but specific processing function.

Why we need OSI model :-

·      Before this model only same venders are communicate & connect to each other.

For example IBM computer connect only a IBM computer

ü HP laptop connected through only a HP pen drive.

·       There are many problem occurs to solve its problem OSI model is develop.

·      In OSI model different vendors are communicate to each other.

For example HP laptop connect by a DELL laptop

Layers of OSI model :-

1.   Physical Layer :-

·       It is first layer of OSI model.

· It is responsible for Electrical, Mechanical , Functional & Procedural checks aspect for Physical Communication.

·  It tells about how is actual data move through the network interfaces in the physically.

·       Defines a relationship between a device & transmission media.

·   Provide the hardware means of sending & receiving data on a carrier.

·       It convert the Signal into the Binary Form.

·  Data will be in the form of Electrical pulses if it is Coaxail or Twisted pair cable & in the form of Light if it is fibre optic cable  .

·       It performs some tasks:-

ü Transmission Media:- it decides that which type of cables, media, connectors are use or how is NIS operate. & networks are wired or wireless.

ü Encoding & Signaling :-in a device or system ↔↔↔↔￣￣￣￣￣￣data is in the form of binary.so this layer tells that how is  the data send or receive in the binary form. or what type of voltages are used for sending  the signal.

ü Topology :- it tells about that how are networks connected to each other physically.

·       DEVICES are :- Hubs , Repeaters , Cables , Modems, Connecter.

For example there are two devices (A & B).they are connected to each other & share the data in the binary form.

2.   Data Link Layer:-

·       It is second layer of OSI model.

·       Access to media ( it decide that how & when device access the media & when the device transfer the data) the techniques are used in CSMA/CD & TOKEN RING.

·       It deals only a two system that are connect only a LAN.

·       It define about the boundries of function.

·       Provide reliable transfer of data access media because it has a physical address.

·       Transfer frames node to node based on station address.

·       It has a some responsibility:-

ü Frame :- it is a datagram when data come in the form of binary form or packet then it become a frame.

ü Error Detection :- when data is transfer then each layer use a header part but only data link layer also use a trailer because it has a FRAME CHECK SEQUENCE value. when data transfer then receiver check & compare the value of FCS & priority valve if both values are same then there are no error otherwise data is in corrupt form.

ü Physical Addressing :- it is a unique identification that is print on lancard it never change.

ü Network Topology ;- it tells about how do network work in a logical manner.

ü Flow Control:- it is a very important features of data link layer. It check the speed of data.

·       Devices are :- SWITCH , BRIDGE , NIC.

3.   Network layer :-

·       It is a third layer of OSI model.

·       it define how is internetwork function.

·       It deals about the two system either data is in a remote location or LAN.

·       Functions used in a Networks layer that are:

ü Packet :- datagram unit of network layer is called PACKET.

ü Logical Addressing :-when devices are communicate to each other then it need a logical address.so logical address is also called a LAYER 3 ADDRESS.

For example :-INTERNET PROTOCOL or IP address. It consist of 32 BIT. if network follow a TCP/IP root then it use a IP address.

                       172.16.0.1

It is not a hardware address but it is a unique id of internetwork.

ü Internetworking:- when two or more than two networks communicate to each other it is called internetwork.

ü Routing :- one or than one device or system transfer the data then they use path. Routing is a best path to reach the destination point.it helps to move the data in multiple network or a system.

ü Error Handling & Diagnostics:- it defines about a protocol.

  For example:- ICMP.

·       DEVIES are :- ROUTER & LAYER 3 SWITCH

4.   Transport layer :-

·       It is the fourth layer of OSI model.

·       It is responsible for end to end connectivity because this layer is in between a upper or lower layer.

·       It is also known as a HEART OF OSI.\

·       It provide data recovery service(only tcp service used).

·       Header add on the data.

·        Essemble of data into single data stream.

·       It performs many task:-

ü Identifying Service

ü Multiplexing & Demultiplexing :- it send a data into a many to one form or one to many form.

ü Error Correction:- if some message miss then it send a message again & again so error remove then message send to a receiver.

ü Flow Control :- it tells about the speed of packets that how much spped is data transfer or receive.

ü Segmentation :- it divide the packet or message into a small part.

ü Sequencing & Reassembling :- it transfer  a data in a way of sequence.

5.   Session layer:-

·       It is the fifth layer of OSI.

·       It solve the problem related to software application & decide that how to communicate between software.

·       This layer responsible for make a session, manage a session, & close the application between the end user.

·       The session application becomes through a request or response between a application.

  For example web browser ,FTP when we transfer the file different sides in a document then session maintain by this application.

·       It select the type of communication like as simplex, half duplex, full duplex.

·       Functions are performed by this :-

ü Establishing connection

ü Maintaining session

ü Synchronizing communication

ü Controlling dialogue

ü Terminating connection

·       Services provide by it:-

ü Authentication:- it is responsible for proof the identity.

ü Permissions:- it give the permission that on which level it access the end user’s request.

ü Session Restoration:- when session break then it again become session.

6.   Presentation layer:-

·       It is the sixth layer of OSI.

·       It is responsible for converting data into standard formate.

·       When two system connect to each other & share the data then some time receiver is not able to view the data so presentation layer is responsible for make a presentable data in both side & assure.

·       It perform some function:-

ü Translation:- in a network there are a different type of platform like as a Microsoft operating system , linux , Unix etc. these operating system are different then there are a different way to access the data so this layer generify the data.

For example internet.

ü Encryption:- it change the data into a encoding form.

NOTE:- transport layer & network layer is also responsible for encrypt the data.

ü Compression:-  it do the small the data or compress the data.

7.   Application layer :-

·       It is a seventh layer of OSI.

·       It is responsible for providing networking sevice to the user.

·       It is also known as desktop layer.

·       Interaction with application program & other layers of OSI models or management the function to support the distribute application.

·       Identification of services is done using the port numbers.

·       It perform many functions:-\\

ü Identifying Communication Partner:- when two system are connect to each other it show that the communication device are available or not to share the data.

ü Determining Resource Availiblity :- when two system share the data then it show that which type of resources or media are use.

ü Synchronizing Communication

ü Error Recovery

ü Data Integrity

ü privacy