N10-009 Question 11
Single answerLayer 5 - SessionA company uses a remote application server that employees access through a terminal services client. Users report that after brief WAN interruptions, they do not need to reauthenticate, and their open application windows reconnect to the same working state once connectivity returns. A network technician is asked which OSI layer function best explains this behavior. Which of the following is the BEST answer?
- A
Layer 5 maintains, synchronizes, and restores the communication session between the client and server
- B
Layer 4 retransmits lost packets and guarantees that the user’s application state is preserved during outages
- C
Layer 3 reroutes traffic after a path failure and automatically recreates the user login session
- D
Layer 7 encrypts the desktop stream and therefore keeps the user logged in during link interruptions
Show answer and explanation
Correct answer: A
Explanation
The best answer is Layer 5. In the OSI model, the Session layer is responsible for establishing, managing, and terminating communication sessions between applications. It also relates to dialog control and synchronization/checkpointing, which are the concepts most closely associated with reconnecting a user to an existing interaction after a brief disruption. In real environments, remote desktop, terminal services, and other interactive client/server applications may provide session persistence or reconnection capabilities that conceptually align with Layer 5 functions, even though actual implementations often span multiple layers. CompTIA Network+ expects candidates to understand the OSI model as a troubleshooting and classification framework: Layer 4 provides transport reliability, Layer 3 provides routing, and Layer 7 provides application services, but session continuity and reconnection behavior map most directly to Layer 5. This aligns with standard OSI model descriptions published in networking textbooks and vendor training materials that define the Session layer as handling session establishment, maintenance, synchronization, and teardown.
- A. Correct.
Correct. The OSI Session layer (Layer 5) is responsible for establishing, managing, and terminating sessions between applications. In practical terms, session-oriented behavior includes dialog control, checkpointing, and session recovery/resumption features used by remote access and application sessions. In this scenario, the key clue is that users reconnect to the same working state without fully starting over, which aligns with Layer 5 session management functions.
- B. Incorrect.
Incorrect. Layer 4, typically associated with TCP and UDP, handles end-to-end transport functions such as segmentation, flow control, port numbers, and reliability for TCP. While TCP retransmission can recover lost data during transient loss, it does not by itself preserve full user application state or restore an interactive login session after an interruption. Confusing transport reliability with session persistence is a common mistake.
- C. Incorrect.
Incorrect. Layer 3 is responsible for logical addressing and routing packets between networks. Dynamic routing can help traffic find an alternate path after a network issue, but routing does not recreate an authenticated user session or restore application context. This option is plausible because WAN interruptions often involve routing changes, but that does not explain session continuity.
- D. Incorrect.
Incorrect. Layer 7 refers to the Application layer, where user-facing application services operate. Encryption of a remote desktop stream is more commonly associated with application protocols working with lower-layer security mechanisms, but encryption itself does not explain why the session remains established or resumable. The misconception here is assuming security features are the reason for session recovery.