In the following pairs of OSI reference layers/sublayers and their…
2018
In the following pairs of OSI reference layers/sublayers and their functionality, the incorrect pair is
- A.
network layer and routing
- B.
data link layer and bit synchronization
- C.
transport layer and end-to-end process communication
- D.
medium access control sublayer and channel sharing
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Correct answer: B
The OSI reference model divides network communication into seven layers, each owning one distinct, well-defined functional responsibility; correctly matching a layer/sublayer to its function requires knowing precisely which layer owns which job, since the Physical and Data Link layers (which both deal with the physical link) are the pair most often confused.
Physical layer: transmission of raw bits over the medium, including bit synchronization (clocking the bit stream so sender and receiver agree on bit boundaries).
Data Link layer: framing, physical/MAC addressing, and error and flow control between two directly connected nodes.
Network layer: logical addressing and routing of packets across interconnected networks.
Transport layer: end-to-end (process-to-process) delivery between source and destination hosts, with segmentation and reliability.
Medium Access Control (MAC) sublayer, part of the Data Link layer: arbitrating access to a shared transmission channel among multiple devices.
Checking each listed pairing against these standard functions:
Pair | Function actually owned by | Verdict |
|---|---|---|
Network layer & routing | Network layer (matches) | Correctly matched |
Data link layer & bit synchronization | Physical layer, not Data Link layer | Mismatched |
Transport layer & end-to-end process communication | Transport layer (matches) | Correctly matched |
MAC sublayer & channel sharing | MAC sublayer (matches) | Correctly matched |
Cross-check: bit synchronization is a bit-level, clock-timing function that every standard OSI reference (e.g. Tanenbaum, Forouzan) places in the Physical layer, one layer below the Data Link layer — so pairing "data link layer" with "bit synchronization" assigns a Physical-layer job to the Data Link layer. The other three pairings (routing to Network, end-to-end delivery to Transport, channel sharing to the MAC sublayer) are the standard, undisputed textbook attributions, so exactly one pairing among the four is mismatched.