GATE2025_CS1_Q16

Identify the ONE CORRECT matching between the OSI layers and their corresponding functionalities as shown.

OSI Layers	Functionalities
(a) Network layer	(I) Packet routing
(b) Transport layer	(II) Framing and error handling
(c) Datalink layer	(III) Host to host communication

✅ Final Answer:

The correct matching is (a)-(I), (b)-(III), (c)-(II), which corresponds to option (B).

🔹 Short Answer:

The standard functionalities of the given OSI layers are:
- Network Layer (a) is responsible for logical addressing and path determination across a network, which is Packet routing (I).
- Transport Layer (b) provides end-to-end (or Host-to-host) communication (III), managing data flow and reliability.
- Datalink Layer (c) is responsible for organizing bits into frames and handling errors within a single network link, which is Framing and error handling (II).
This matches option (B).

🔸 Long Answer:

To solve this question, we need to correctly recall the primary functions of the Network, Transport, and Datalink layers in the OSI (Open Systems Interconnection) model.

Analyzing Each Layer and its Functionality:

1. (a) Network Layer:
   The Network Layer (Layer 3) is responsible for providing logical addressing (like IP addresses) and determining the best path for data packets to travel from a source to a destination across multiple networks (or "internetworks"). This process of path determination and forwarding packets is called routing.
   Therefore, Network Layer (a) correctly maps to (I) Packet routing.
2. (b) Transport Layer:
   The Transport Layer (Layer 4) provides transparent data transfer between end systems, or hosts. It is responsible for end-to-end connection management, segmentation of data, flow control, and error recovery. This ensures reliable data delivery from a process on the source machine to a process on the destination machine. This is commonly referred to as host-to-host communication or process-to-process delivery.
   Therefore, Transport Layer (b) correctly maps to (III) Host to host communication.
3. (c) Datalink Layer:
   The Datalink Layer (Layer 2) is responsible for node-to-node (or hop-to-hop) data transfer. It takes the packets from the Network Layer and encapsulates them into units called frames. It also adds headers and trailers with physical addresses (like MAC addresses) and performs error detection/correction for the data within a single link.
   Therefore, Datalink Layer (c) correctly maps to (II) Framing and error handling.

Matching Summary:

Based on the analysis, the correct pairings are:

Layer	Correct Functionality	Matching
(a) Network layer	(I) Packet routing	(a)-(I)
(b) Transport layer	(III) Host to host communication	(b)-(III)
(c) Datalink layer	(II) Framing and error handling	(c)-(II)

This set of matches—(a)-(I), (b)-(III), (c)-(II)—corresponds exactly to option (B).

Bibliography:
- Tanenbaum, A. S., & Wetherall, D. J. (2011). Computer Networks (5th ed.). Pearson Education. (Chapter 1: The OSI Reference Model).
- Kurose, J. F., & Ross, K. W. (2016). Computer Networking: A Top-Down Approach (7th ed.). Pearson. (Chapter 1: Protocol Layers and Their Service Models).

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