•   Physical Layer—Defining the electrical and mechanical interfaces to the network, it determines the upper limit of the transmission speed needed for audio and video information.

    •   Data Link Layer—Comprising the access protocol to the physical layer, it deals with error correction, flow control, frame synchronization, and the transmission of data frames.

    •   Network Layer—Containing switches and router packets, it establishes logical associations of remote stations and provides services such as addressing, congestion control, error handling, internetworking, and packet sequencing.

    •   Transport Layer—Provides a program-to-program connection.

    •   Session Layer—Coordinates interactions between user application processes on different hosts, including multi-cast (defined as one to many, multi-drop), many-to-one sessions, and point-to-point.

    •   Presentation Layer—Manages abstract data structures and converts different data formats and codes.

        •   Application Layer—Contains protocols such as ftp, SMTP, telnet, and email.

The TCP/IP protocol used on the Internet collapses layers 5, 6, and 7 of the above OSI Model to a single application layer, thus forming a five-layer protocol.

See Also: Encapsulation; TCP/IP.