In IEEE 802 LAN standards, the Data Link layer is split into two sublayers for clarity of responsibilities. Which names correctly identify the upper sublayer and the lower sublayer, respectively?

Introduction / Context:
Local Area Network (LAN) standards from IEEE project 802 refine the classic OSI Data Link layer by splitting it into two logical parts. This split helps vendors and engineers cleanly separate concerns: one sublayer focuses on addressing and media access to the physical medium, while the other offers a uniform service interface and control to higher layers regardless of the underlying media details.

Given Data / Assumptions:

• The question refers to IEEE 802 LAN architecture.
• We must name the upper and lower Data Link sublayers in their correct order.
• Common LANs (Ethernet, Wi-Fi, Token Ring historically) follow this structure.

Concept / Approach:
IEEE 802 defines the Logical Link Control (LLC) as the upper sublayer and the Media Access Control (MAC) as the lower sublayer. The LLC sublayer provides a consistent interface (service access points, flow/error control primitives) to the Network layer. The MAC sublayer implements addressing (e.g., 48-bit MAC addresses) and media access rules (CSMA/CD, CSMA/CA, token passing, etc.).

Step-by-Step Solution:
Identify the role of the upper sublayer: uniform services to Layer 3 → LLC.Identify the role of the lower sublayer: frame formatting, media access, addressing → MAC.Map to options in correct order: upper = LLC, lower = MAC.

Verification / Alternative check:
Ethernet frames include a MAC header/footer handled by MAC; LLC (historically IEEE 802.2) sits above and can multiplex protocols such as IP and IPX via Service Access Point (SAP) values, though modern Ethernet commonly uses EtherType directly (bypassing classic LLC for many protocols). The architectural split, however, remains core to IEEE 802 documentation and pedagogy.

Why Other Options Are Wrong:
HDLC/PDU or PDU/HDLC: HDLC is a distinct bit-oriented protocol, and PDU is a generic term for protocol data unit, not a sublayer.

MAC, LLC: Reversed order; MAC is lower, LLC is upper.

None of the above: Incorrect because LLC (upper) and MAC (lower) is the standard answer.

Common Pitfalls:
Confusing OSI Data Link framing with IEEE’s sublayer split; remember that “LLC on top, MAC below” is the canonical mapping used in 802 LANs.

Final Answer:
LLC, MAC