Error detection and recovery takes place at which layer?
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transport
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presentation
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data link
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netwrok
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application
To answer this question, the user needs to know about the different layers of the OSI model and their functions.
Error detection and recovery are functions that are performed at different layers of the OSI model, but the most common layer where it takes place is the Transport layer.
Options A, B, and E are incorrect because error detection and recovery do not take place at the Transport layer.
Option C, Data Link layer is also incorrect, because this layer is responsible for error detection and correction only for the local network segment.
Option D, Network layer is also incorrect, because this layer is responsible for routing and logical addressing.
Therefore, the correct answer is:
The Answer is: A (Transport)
The Transport layer (Layer 4) is responsible for reliable end-to-end delivery, which includes error detection and recovery via mechanisms like checksums, acknowledgments, and retransmission (as seen in TCP). This is why it's the textbook answer for error detection and recovery. The Presentation layer handles data formatting/encryption, not error recovery; the Data Link layer does perform error detection (e.g., CRC) but only for single-link hops, not end-to-end recovery; the Network layer handles routing/addressing; and the Application layer deals with user-facing services. Transport is the layer explicitly tasked with guaranteeing correct, complete delivery across the whole path.