What is the function of the Session Layer of the OSI model?

The Session Layer is responsible for establishing, maintaining, and terminating a connection called a 'session'. A session is an exchange of messages between computers (a dialog). Managing the session involves synchronization of user tasks and dialog control (e.g., who transmits and for how long). Synchronization involves the use of checkpoints in the data stream. In the event of a failure, only the data from the last checkpoint has to be resent.

Logon, name recognition and security functions take place at the Session Layer. Winsock and NetBIOS are usually shown as functioning at the session layer.