Which OSI layer is responsible for reliable end-to-end communication and error recovery?

Question

BlackTom AI · Accepted Answer

The Transport layer (Layer 4) provides reliable end-to-end communication and error recovery.

1) Relevant knowledge points and concepts
- OSI model layering: Data Link (Layer 2), Network (Layer 3), Transport (Layer 4), Session (Layer 5).
- Transport layer responsibilities: end-to-end data delivery, segmentation/reassembly, flow control, error detection and recovery (e.g., acknowledgments and retransmissions), and logical port addressing. Protocol examples: TCP (reliable, connection-oriented) and UDP (unreliable, connectionless).
- Data Link handles node-to-node (link) delivery and frame-level error detection/correction; Network handles routing and logical addressing; Session manages dialogs and synchronization.

2) Step-by-step reasoning
- The question asks for the layer responsible for reliable end-to-end communication and error recovery. “End-to-end” implies between source and destination hosts (not just on a single link).
- Transport layer is explicitly defined to provide host-to-host (end-to-end) services. Mechanisms like sequence numbers, ACKs, timeouts, and retransmissions implement error recovery and ensure reliable delivery (as in TCP).
- Layers below (Data Link, Network) primarily deal with single-link error handling and routing; Session focuses on managing and synchronizing sessions rather than performing packet-level error recovery.

3) Calculations
- No numerical calculations are required for this conceptual question.

4) Why the correct answer is correct
- The Transport layer implements reliability features (segmentation, sequence numbering, ACKs, retransmission, flow/congestion control) that achieve reliable end-to-end communication and error recovery across an entire path between hosts.

5) Why the other options are incorrect
- a. Network: Responsible for routing and logical addressing (IP); it does not provide end-to-end reliability.
- c. Session: Manages sessions, checkpoints, and dialog control; it does not implement packet-level error recovery.
- d. Data Link: Provides error detection/correction on a single physical link (frames), not end-to-end host-to-host reliability.

6) Conclusion
This supports and confirms the provided answer: b. Transport.

Which OSI layer is responsible for reliable end-to-end communication and error recovery?单项选择题

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