OSI stands for Open System Interconnection.
OSI model is a model which defines the communication between two or more nodes in a network.It elaborates how the transmission of data between two computers can be done. OSI model was developed by ISO( International organisation of standardisation)
OSI MODEL has 7 layers-
1. Physical Layer(P)
2. Data Link Layer(D)
3. Network Layer(N)
4. Transport Layer(T)
5. Session Layer(S)
6. Presentation Layer(P)
7. Application Layer(A)
[Note:- Here is a trick to remember the sequence of layers- Take the first letter of each layer PDNTSPA and recall it as Please Do Not Throw Sauce Pizza Away]
1.Physical Layer :-
Physical Layer is the first layer of OSI Model.
It is directly connected with the transmission medium.here, bit transmission is done.
Functions of physical layer-
1. Line Configuration- medium(e.g-ethernet)
2. Transmission mode- Modes can be Simplex(at a time data can be sent or received from one end only), Half duplex (data can be sent or received from both ends but not at the same time )
, Duplex (data can be sent or received from both ends at the same time)
3. Signals- signals are transmitted to the network.
2.Data-Link Layer:-
Data Link is responsible for error-control and flow-control for the data frames to be transferred . the MAC address (source to destination) is stored in the header of data link layer. It is also used to convert the packets into frames.
Data Link Layer is sub divided into two groups-
1. Logical Link Control Layer- This layer is
used to transfer the data into network layer.
2. Mobile Access Control- This layer lies between Logical Link Control layer and data link layer
Functions of Data link layer-
1. Framing.
2. Addressing.
3. Error-control- An error detecting code CRC(cyclic redundancy check).it is present in the trailer of Data link layer.
4. Flow-control.
5. Access-control.
Network Layer-
Network layer is responsible for tracking the location of data packets
Functions-
1.Internetworking
2.IP addressing
3.Packetising.
Transport Layer-
Transport Layer is responsible for the transmission of data in a proper sequence in which order they have sent in the same order they need to be received. there should be no duplication of data.
Protocols-
1.Transport Control Protocol-TCP protocol divides the packets into small segments and then at the receiver end the segments are sequenced in a proper manner.
2.UDP[User Datagram Protocol]-Not reliable[connectionless service]
Functions-
1. Segmentation and assembly.
2. Port addressing.
3. Connection Control.
Session Layer-
It is responsible for the transfer of data reliably. it decides when to end the session it basically manages the session
It adds the checkpoints in the data so when the data will be lost then we don't need to re send the data from the beginning.
Function-
Synchronization.
Presentation Layer-
Presentation Layer works on syntax and semantics and is responsible for Translation, Encryption and Compression between two systems.
It is also called Syntax Layer.
Application Layer-
Application Layer provides a window for users to communicate between the devices.
It provides network services to end user.
