The Session layer of the OSI model

[aguila3380]

From what I understand the Application layer provides the interface for a user to interact with an Application such as e-mail, and FTP, and that the Presentation layer is reaponsible for how data is represented to the user through that interface (like text with ASC II), but how does the Session layer use the transport layer, and work with the Presentation layer to setup, and tear down calls? If you could, use NFS(Network File System), and RPC(remote-procedure call) in your examples.

[Josef Oduwo]

Alex,

The Session (Layer 5) protocol defines the format of the data sent over the connections. NFS uses the Remote Procedure Call (RPC) for its session protocol.

RPC may be built on either TCP or UDP (both of which are Layer 4). Login sessions use TCP whereas NFS and broadcast use UDP.

A quick note on the two Transort (Layer 4) protocols: TCP keeps track of the packet delivery order and the packets that must be resent. Maintaining this information for each connection makes TCP a stateful protocol. UDP, on the other hand, provides a low overhead transmission service, but with less error checking. NFS is built on top of UDP because of its speed and statelessness, which simplifies crash recovery.

Josef.

PS - please rate the usefulness of the post ;-)