OSI Model

OSI Model

1. Open System Interconnection

   • Defines how messages should be transmitted from one device to another

2. Application (layer 7)

   • Supports application and end user processes
   • Partners identified, quality identified, user authentication and privacy considered
   • Constraints on data syntax identified
   • Application specific

3. Presentation (Layer 6) - sometimes known as syntax layer

   • Provides independence from differences in data representation (encryption)
   • Translate from application to network format
   • Works to transform data into form that application layer can accept it
   • Encrypts data to be sent across a network

4. Session (Layer 5)

   • Establishes, manages and terminates connections between applications
   • Sets up, coordinates, and terminates exchanges between applications at each end.
   • Deals with session and connection coordination

5. Transport (Layer 4)

   • Provides transparent transfer of data between end systems, or hosts and is responsible for end to end error recovery and flow control
   • Ensures complete data transfer

6. Network (Layer 3)

   • Provides switching and routing technologies, creating logical paths known as virtual circuits for transmitting data from node to node
   • Addressing, inter-networking, error handling, congestion control and packet sequencing

7. Data Link (Layer 2)

   • Data packets encoded and decoded into bits.
     • Handles errors in physical layer, flow control and frame sync
   • 2 sub-layers
     • Media Access Control (MAC)
       • Controls how network gains access to data and permission to transmit it
     • Logical Link Control (LLC)
       • Controls frame sync, flow control and error checking

8. Physical (Layer 1)

   • Coveys bit stream
     • Electrical impulse, light or radio signal
     • Provides hardware means of sending and receiving data on a carrier

9. Benefits

   • Independent of country
   • Any hardware/ software that meets OSI standard can communicate
   • Consumers have a wider range of choice
   • Not dependant on operating system