Lesson Plan

• Describe Ethernet frame structure and the minimum frame‑size requirement.
• Explain how CSMA/CD detects and resolves collisions on a shared medium.
• Calculate propagation delay and relate it to the minimum Ethernet frame size.
• Compare half‑duplex (collision‑prone) and full‑duplex (collision‑free) Ethernet operation.
• Evaluate alternative MAC protocols such as CSMA/CA and Token Ring.

• Projector or interactive whiteboard
• Slides covering Ethernet, frame structure, and CSMA/CD
• Ethernet cable and a half‑duplex switch for a live demo
• Handout with frame diagram and collision timeline
• Network simulator software (e.g., Cisco Packet Tracer)
• Worksheet for propagation‑delay and back‑off calculations

Begin with a short video showing data packets colliding on a busy network cable. Ask students what they already know about sharing a common medium and why collisions might occur. Explain that by the end of the lesson they will be able to trace a CSMA/CD transmission and calculate the minimum Ethernet frame size.

1. Do‑now (5') – Quick quiz on OSI layers and basic Ethernet terminology.
2. Direct instruction (10') – Present Ethernet frame fields, data rates, and minimum frame size using slides.
3. Demonstration (10') – Live demo with two computers on a half‑duplex switch showing a collision, jam signal, and back‑off.
4. Guided practice (15') – Pairs calculate propagation delay and back‑off times from the worksheet; teacher circulates for support.
5. Consolidation (10') – Class discussion comparing half‑duplex CSMA/CD with full‑duplex and other MAC protocols; students complete an exit‑ticket.

Recap how CSMA/CD detects collisions, sends a jam signal, and uses exponential back‑off before retransmission. Students write one key takeaway on an exit ticket. For homework, research how Wi‑Fi employs CSMA/CA and prepare a brief comparison.