IEEE 802 family: which standard specifically defines classic Ethernet media access and physical specifications (the CSMA/CD-based LAN standard)?

Introduction / Context:
The IEEE 802 project organized LAN/MAN standards by technology families. Recognizing which number corresponds to Ethernet is fundamental for networking exams, vendor certifications, and standards literacy.

Given Data / Assumptions:

• We need the standard that defines classic Ethernet (originally CSMA/CD).
• The options list several IEEE 802 working groups/sub-standards.
• We focus on the correct numeric mapping, not operational details.

Concept / Approach:
IEEE 802.3 defines Ethernet physical/MAC layers and has evolved from shared coax to twisted pair and fiber at speeds from 10 Mbps to multi-100 Gbps+. IEEE 802.2 historically defined LLC, 802.4 was token bus, 802.5 token ring, and 802.6 metropolitan area networks—none of which are the Ethernet spec itself.

Step-by-Step Solution:

Verification / Alternative check:
Vendor datasheets and standards references cite 802.3 for Ethernet PHY/MAC features such as autonegotiation, twisted-pair cabling (100BASE-TX, 1000BASE-T), and fiber variants—confirming this mapping.

Why Other Options Are Wrong:

• 802.2: Logical Link Control, not Ethernet MAC/PHY.
• 802.4: Token Bus.
• 802.5: Token Ring.
• 802.6: MAN standardization, not Ethernet.

Common Pitfalls:
Confusing 802.2 (LLC) with 802.3 (Ethernet) because both appear in older layered diagrams.

Final Answer:
802.3