In the OSI model, which statement best reflects a core function provided by the Network layer (Layer 3) rather than the Data Link layer?

Introduction:
The OSI model separates responsibilities so that each layer solves a specific part of the end-to-end communication problem. This question checks whether you can distinguish what truly belongs to the Network layer (Layer 3) versus what is confined to the Data Link layer (Layer 2).

Given Data / Assumptions:

• Layer 2 (Data Link) handles framing, link-local addressing, and error detection over a single hop.
• Layer 3 (Network) handles logical addressing, routing, and end-to-end packet delivery across multiple hops.
• X.25 provides an example of Layer-3 virtual circuits (PLP) across a packet network.

Concept / Approach:
The Network layer’s hallmark is inter-network delivery: routing between subnets and often providing a virtual-circuit abstraction (as in X.25). Data Link focuses on a single link segment (framing, MAC addressing). Therefore, a description that centers on end-to-end virtual circuits for packet-switched services belongs to Layer 3, not Layer 2.

Step-by-Step Solution:

Verification / Alternative check:
In X.25, PLP (Packet Layer Protocol) provides virtual circuits across the network, whereas LAPB (Data Link) manages a single hop. This confirms that end-to-end virtual-circuit service belongs to the Network layer.

Why Other Options Are Wrong:

• A: Layer-2 framing procedures, not Layer-3 routing/service.
• B: References X.25 but is imprecise; the defining Layer-3 function is captured more directly by C.
• D: Cannot be correct because A is Layer-2.
• E: False; C is correct.

Common Pitfalls:
Confusing single-link responsibilities (Layer 2) with multi-hop end-to-end services (Layer 3); assuming “All of the above” when one choice clearly belongs to a different layer.

Final Answer:
Offering a virtual-circuit interface to a packet-switched service for end-to-end delivery.