Lesson Plan

• Describe the ARQ cycle, including ACK/NAK and timeout handling.
• Compare Stop‑and‑Wait, Go‑Back‑N, and Selective Repeat ARQ protocols.
• Calculate the probability of successful transmission using ARQ formulas.
• Explain why ARQ is essential for reliable data communication.
• Apply ARQ concepts in a simple network‑simulation activity.

• Projector or interactive whiteboard
• Slide deck covering ARQ concepts
• Handout with ARQ flowchart and probability formulas
• Short video demonstration of ARQ in action
• Laptops/tablets with a network‑simulation tool (e.g., Packet Tracer)
• Whiteboard markers and sticky notes for group work

Begin with the question, “How does the internet know a packet arrived correctly?” Connect this to previous lessons on error‑detecting codes such as checksums and CRC. Explain that today’s success criteria are to trace the ARQ cycle, compare its variants, and calculate its reliability.

1. Do‑Now (5’): Students write their answer to the opening question on sticky notes; teacher collects and discusses common ideas (quick check).
2. Mini‑lecture (10’): Present the ARQ process, ACK/NAK, timeout, and sequence numbers using slides and a flowchart diagram (thumbs‑up check).
3. Guided Practice (12’): Walk through the basic ARQ steps on the board, filling in a blank flowchart together.
4. Protocol Comparison Activity (10’): In small groups, students analyse Stop‑and‑Wait, Go‑Back‑N, and Selective Repeat using the handout and complete a comparison table.
5. Simulation Exercise (10’): Learners use a network‑simulation tool to model a frame transmission with ARQ, observing retransmissions and timeout behavior.
6. Exit Ticket (3’): Each student writes one sentence explaining why a timeout is required in ARQ.

Review the ARQ cycle and the key differences among the three protocols, highlighting how they improve reliability. Collect exit tickets to gauge understanding, then assign a short reading on TCP’s use of ARQ and a probability problem for homework.