OSI Reference Model

• The OSI reference model consists of seven layers: physical, data-link, network, transport, session, presentation, and application.
• The OSI model layers usually do not correspond exactly to the protocol stack running on an actual system.
• The data-link layer protocols often include physical layer specifications.
• The network and transport layer protocols work together to provide a cumulative end-to-end communication service.
• The functions of the session, presentation, and application layers are often combined into a single application layer protocol.