The International Organization for Standardization (ISO) defined the Open Systems Interconnection (OSI) reference model to standardize networking of devices from different vendors. The OSI reference model is mostly an architecture blueprint that networking and computer device manufacturers implement. The OSI model has never been implemented exactly as defined. The TCP/IP protocol stack is the closest implementation available today.
Application Layer (7)
This layer represents the various network applications such as e-mail reader, Web browser, Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), and Network File System (NFS). ✦ The application layer provides a user interface and processes network data. ✦ The application layer on the sending host produces the network data to be transmitted from the sender host. ✦ The application layer on the receiving host consumes the network data produced and transmitted by the sender host.
Presentation Layer (6)
This layer is mostly concerned with data format. It converts the data between different formats so that both the sender and the receiver can use heterogeneous data. For example, mail messages contain various data formats: text, application attachments, video, audio, and graphical signature. ✦ The presentation layer on the sending host receives the data payload from the application layer. ✦ The presentation layer on the sending host converts the data into a format that is easily transportable over the network. ✦ The presentation layer on the receiving host converts the data from the network format back to its native format that can be easily interpreted, used, and displayed by the application layer above.
Session Layer (5)
Some applications need to open logical communication channels between the computer hosts. Logical communication channels (sessions) maintain data about the communication established between the network application running on the...