Layer 7 – The Application Layer
The application layer provides network services to the applications of the end user. It differs from the other layers because it does not provide services to any other OSI layer.
It establishes the availability of intended partners and it then synchronizes and establishes agreements on procedures for error recovery and control of data integrity.
Layer 6 – The Presentation Layer
The presentation layer ensures that the information that is sent at the application layer of one system is readable by the application layer of another system.
The presentation layer can translate among multiple data formats using a common format (e.g computers with different encoding schemes)
Layer 5 – The Session Layer
The session layer establishes, manages and terminates sessions between two communicating hosts. The session layer also synchronizes dialog between the presentation layers of the two hosts and manages their data exchanges e.g web servers have many users, so there are many communication processes open at any given time to track. It also offers efficient data transfer, class of service (COS) and exception reporting of any upper layer problems.
