The connection manager, coordinating and keeping conversations in sync.
PDU: Data / Session
Focus: Dialogue & Checkpoints
Hardware: CPU / Auth Servers
Core Purpose & Function
While the lower layers manage the delivery of raw packets or segments, the Session Layer is the high-level manager that understands the *lifetime* of the conversation. It handles user authentication, session token mapping, and coordinates which party is allowed to talk (dialogue control).
Key Responsibilities
Session Creation & Teardown: Gracefully opening a communication channel, authenticating users, assigning session IDs, and tearing down the channel when done.
Synchronization & Checkpointing: Injecting checkpoints (recovery markers) into a data stream. If a 100MB download is interrupted at 80MB, session checkpoints allow the transfer to resume from the last marker instead of restarting from scratch.
Dialogue Control: Coordinating half-duplex (alternating sender/receiver) or full-duplex (simultaneous) transmission streams so packets don't overlap in confusing sequences.
Common Technologies & Protocols
| Protocol / Standard | Description | Role in Session Management |
|---|---|---|
| SOCKS | Socket Secure Protocol | Routes packets through proxy servers, establishing authenticated sessions. |
| RPC / gRPC Sessions | Remote Procedure Call | Makes remote servers look like local functions, managing transaction states. |
| NetBIOS | Network Basic Input/Output System | Sets up sessions and connections between local Windows computers. |
| PPTP / L2TP Sessions | Point-to-Point Tunneling Protocols | Establishes persistent, encrypted tunnels for VPN sessions. |