Identify the ONE CORRECT matching between the OSI layers and their corresponding functionalities as shown.
Tap to open full sizeA two-column table. Header: OSI Layers | Functionalities. Rows: (a) Network layer | (I) Packet routing; (b) Transport layer | (II) Framing and error handling; (c) Datalink layer | (III) Host to host communication.
(a)-(I), (b)-(II), (c)-(III)
(a)-(I), (b)-(III), (c)-(II)
(a)-(II), (b)-(I), (c)-(III)
(a)-(III), (b)-(II), (c)-(I)
ANSWER
Option B: (a)-(I), (b)-(III), (c)-(II).
Official answer: BSource: Official answer key, GATE 2025 CS1 (IIT Roorkee)
The network layer is responsible for moving packets from the source to the destination across networks, which needs routing. So (a) Network layer matches (I) Packet routing.
The transport layer gives end-to-end delivery between the communicating hosts, with port numbers identifying the processes at each end. Of the three functions listed, this is closest to (III) Host to host communication. So (b) matches (III).
The data link layer groups bits into frames and detects or handles errors on a single link. So (c) Datalink layer matches (II) Framing and error handling.
The matching is (a)-(I), (b)-(III), (c)-(II), which is option B. Option A pairs (b) with (II) and (c) with (III), which is wrong. Option C pairs (a) with (II) and (b) with (I), which is wrong. Option D pairs (a) with (III) and (c) with (I), which is wrong.
KEY IDEA
Match each OSI layer to its core job. The network layer routes packets, the transport layer provides end-to-end (host to host) communication, and the data link layer does framing and error handling on one link.
WATCH OUT FOR
Pairing the transport layer with framing and error handling, or the network layer with host to host communication. Framing belongs to the data link layer, and end-to-end delivery belongs to the transport layer.
From the GATE 2025 CS1 paper. Every question of this paper · Download the full paper · All 2 Layering & switching questions, with notes