OSI Model

OSI Model consists of 7 layers in total, respective names of which are depicted in diagram given below along with their respective positions as Outward and Inward Layers

OSI Model is a Linkage Framework of these seven layers each of which has a distinct role and authority area e.g. Network, Data Linking, User Interface etc. 

Significance of each of these seven Layers has been explained below--

1. Layer 1 – Physical Layer :
• Hardware Layer
• Specifies Mechanical as well as Electromagnetic features of communication between devices and transmission
• Network Topology is part of this Layer
2. Layer 2 – Data Link Layer :
• Hardware Layer
• Specifies “Channel Access Control Method”
• Ensures reliable data transfer through transmission medium
3. Layer 3 – Network Layer :
• Makes a choice of Physical Route of transmission
• Creates a Virtual Circuit for upper  layers
• Establishes, Maintains & Terminates connections between nodes and ensures proper routing of Data
4. Layer 4 – Transport Layer :
• Ensures reliable transfer of Data between User Processes, Assembles & Disassembles  message packets
• Provides Error Recovery and Flow Control
• Multiplexing & Encryption are undertaken at this Layer Level
5. Layer 5 – Session Layer :
• Establishes, Maintains & Terminates “Sessions” or what we can say “Dialogues” between user processes
• Identification & Authentication are undertaken at this Layer
6. Layer 6 – Presentation Layer :
• Controls “On Screen” display of Data and transforms data to a Standard Application Interface
• Encryption, Data Compression can also be undertaken at this Layer Level
7. Layer 7 – Application Layer :
• Provides User services such as File Transfer, File Sharing etc.
• Database Concurrency & Deadlock Situation Controls are undertaken at this Layer Level