Layer manages sessions between applications. A session is a sustained exchange of information.
Primary functions:
- Establishment: setting up connections
- Maintenance: keeping sessions alive
- Termination: closing cleanly
Session management includes checkpointing. If a transfer fails halfway, the session can resume instead of restarting.
In practice, applications handle sessions themselves. NetBIOS and PPTP are session-layer protocol examples. Modern TCP/IP apps implement session logic directly.