OSI MODEL

OSI MODEL

1. LAYER 1 - Physical - The physical layer, the lowest layer of the OSI model, is concerned with the transmission and reception of the unstructured raw bit stream over a physical medium. It describes the electrical/optical, mechanical, and functional interfaces to the physical medium, and carries the signals for all of the higher layers

   • Physical Medium Attachment
     • Data Encoding
       • Physical Medium Transmission

2. LAYER 2 - Data Link - The data link layer provides error-free transfer of data frames from one node to another over the physical layer, allowing layers above it to assume virtually error-free transmission over the link

   • Frame Sequecing
     • Frame acknowledgment
       • Frame error checking
         • Frame traffic control

3. LAYER 3 -Network - The network layer controls the operation of the subnet, deciding which physical path the data should take based on network conditions, priority of service, and other factors

   • Routing
     • Frame fragmentation
       • Logical-physical address mapping
         • Packets

4. LAYER 4 - Transport - The transport layer ensures that messages are delivered error-free, in sequence, and with no losses or duplications. It relieves the higher layer protocols from any concern with the transfer of data between them and their peers

   • Message segmentation
     • Message acknowledgment (TCP, UDP)
       • Message traffic control
         • Session multiplexing

5. LAYER 5 - Session - The session layer allows session establishment between processes running on different stations

   • Session establishment, maintenance and termination
     • Session support

6. LAYER 6 - Presentation - The presentation layer formats the data to be presented to the application layer. It can be viewed as the translator for the network. This layer may translate data from a format used by the application layer into a common format at the sending station, then translate the common format to a format known to the application layer at the receiving station

   • Character code translation
     • Data conversion
       • Data compression
         • Data encryption

7. LAYER 7 - Application - The application layer serves as the window for users and application processes to access network services

   • Resource sharing and device redirection
     • Remote file access
       • Remote printer access
         • Electronic messaging (such as mail)
           • Network management