Networking System - OSI (Open System Interconnection) Model

OSI Layer or Models :-

1. OSI Layer Stands for Open System Interconnection Layers
2. Developed by International Organization of Standardarization (ISO)

LIST OF OSI LAYERS :-

• Application Layer

• Presentation Layer

• Session Layer

• Transport Layer

• Network Layer

• Data Link Layer

• Physical Layer

7th Layer - Application Layer

• It is the very top of OSI Model

• It is implemented at the networks app

• This is where data is acquire which cab be sent over the network

• It gives a window for data to reach the application & its services for displaying/presenting it to user

• Application Layer also known as Desktop Layer

6th Layer -  Presentation Layer

• It is also known as Translation Layer

• While sending the data from application layer is extraction here & manipulated as per the required format to transmit one network

          1. Translation or (Encoding/Decoding) - "UTF-8".ASCII
          2. Encrytion/Decryption
          3. Compression - Defalte/Inflate

5th Layer - Session Layer 

• The connection is established & maintain session
• Does Authentication & Authorization
• And also ensure security
• Session Establishment,Maintanence,Termination :- This layer allows two or more process to esablish,use & terminate the connection
• Sychronization :- Assemble & Dissassemble the date on transmit 
• And also error handling here

4th Layer - Transport Layer

• How does the data reaches to the destination that is called transport layer
• It takes data from network while receiving & takes data from session/presentation/application layers while sending
• The data here is reffered to as segments
• This layer provides the acknowlegdement of successful data transmission & retransmission on error

     While sending :-

• Transport layer receives the formatted data from the upper layers the it performs segmentation and also does & how corrections
• It also adds the destination address & port number in the packet headler & then forwards the segment to the network layer

     While receiving :-

• It reads the port number from the headers & forward the data to the specific application to its binded
• It also does sequencing & reassembly segmented data

           - Function :-

             1. Segmentation & Reassembly 

             2. Service Point Addressing

Service Provided by Transport Layer:- 

     Connection Oriented [TCP (Transmission Control Protocol)] 

• Connection established (SYN-ACK)
• Data transfer
• Termination & disconnection

     Connection-less Oriented [UDP(User Datagram Protocol)]

• No acknowledgement & it is one phase process
• TCP is more reliable

3rd Layer - Network Layer

• It works for the transmission of data frame one host another,which can also located on a different network 
• It does the packet routing 

          1. Selection of shortest path between two hosts
          2. Places senders & receivers IP on theirs headers (logical addresing)

2nd Layer - Data Link Layer

• The main duty of a data link layer is to ensure that packets are being delivered to the correct node in the network
• Yet another duty of the DDL is to provide an error free commincation
• When a packet reaches a network/modem node the responsibility of DLL is to send the packet to the right host

Data Link Layer (DDL) is divided into 2 layers : -

• Logical Link Control (LLC)
• Media Access Control (MAC)

In sending node the packect are being pushed from network layer to DLL where the packets are further divided into frames depending on the frame size of the Network Interface Card (NIC)

DDL & ARP (Address Resolution Protocol)

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