SSC IMD SA 2017 – Question 158

Which of the following layers provides delimiting and synchronization of data exchange?

• Application layer
• Session layer
• Transport layer
• Link layer

Detailed Explanation:

The correct answer is b) Session layer (सत्र लेयर).

In the OSI 7-layer reference model, the Session Layer (Layer 5) provides the mechanism for opening, closing, and managing a session between end-user application processes:

• Dialog Control: Establishes communication modes (half-duplex or full-duplex) between processes.
• Delimiting and Synchronization: The session layer allows a process to insert checkpoints (synchronization points) into the data stream. If a system failure occurs during the transmission of a large data stream (e.g., a 100-page file), only the data transmitted after the last validated checkpoint needs to be resent, rather than restarting the entire transfer from page 1.

Responsibilities of Other Layers:

• Application Layer (Layer 7): Provides network services directly to end-user applications (HTTP, FTP, SMTP).
• Transport Layer (Layer 4): End-to-end delivery, flow control, error recovery (TCP, UDP).
• Link Layer (Layer 2): Framing, physical addressing, hop-to-hop link control.