Within the OSI model, what does the Data-Link layer specify and provide to enable reliable exchange of data over a single physical link?

Introduction / Context:
The OSI model divides network functions into layers. The Data-Link layer (Layer 2) sits above the Physical layer and below the Network layer, providing services necessary to move frames reliably across a single link. This question checks understanding of the Data-Link layer's core responsibilities and how they differ from higher-layer interfaces like X.25 packet services.

Given Data / Assumptions:

• Layer 2 deals with node-to-node delivery on one link.
• Framing, addressing (MAC), and error detection are typical layer-2 functions.
• X.25 packet interfaces belong to the packet (network) layer and its service access points.

Concept / Approach:
The Data-Link layer defines how bits are grouped into frames, how medium access is controlled, and how errors are detected and may be corrected on a single hop. Examples include Ethernet MAC with FCS, and LAPB/LAPD in WAN contexts. By contrast, “the interface between an X.25 network and a packet-mode device” and “the virtual circuit interface to packet-switched service” describe packet layer (Layer 3) service definitions rather than L2 framing procedures.

Step-by-Step Solution:

Verification / Alternative check:
Standards like IEEE 802.3 and ISO LAPB specify framing and link procedures at Layer 2, confirming the correctness of the selected option relative to X.25 packet interfaces at higher layers.

Why Other Options Are Wrong:

• X.25 interface / virtual circuit: packet-layer (network-layer) constructs, not data-link framing.
• All of the above: cannot be correct because the X.25 options are not Layer 2 definitions.
• None of the above: incorrect because one option correctly states Layer 2's role.

Common Pitfalls:
Confusing service access points between layers; assuming that because LAPB is link-layer, all X.25 language refers to Layer 2 (PLP is Layer 3).

Final Answer:
Data-link procedures for exchanging data via frames that can be sent and received.