13 RPL Knowledge Check

What is this chapter? Scenario-based quizzes that test your RPL understanding through realistic deployment situations.

How to approach:

1. Read each scenario carefully
2. Consider all factors before choosing
3. Expand the explanation to learn from the detailed analysis
4. Relate the scenario to your own projects

Scenario: You’re deploying a patient monitoring system across a 300-bed hospital with 1,200 wireless sensors (vital signs, room environment, equipment tracking).

Network requirements: Begin with the dominant upward flow: 1,000 sensors send readings to the cloud every two minutes through the gateway. Then account for the less frequent downward path, where 200 infusion pumps receive dosage updates from nurse stations. Finally, keep the point-to-point path visible: a Room 302 nurse-call button must reach the nursing-station display, with 10—20 events per day on each floor. These three directions, not node count alone, determine which routing state the deployment needs.

RPL Mode Comparison:

Analysis: Start with the many-to-one sensor traffic, for which both modes use parent pointers in the same way. Next, compare the occasional one-to-many pump update. The stated example gives Storing mode a direct two-hop path, while Non-Storing mode adds a 10-byte source-routing header to the two-hop path; at 200 updates per day, the example calculates 2 KB of added daily traffic. The decisive comparison is the nurse-call path. Storing mode can go from Room 302 through the floor router to the nursing station in two hops, whereas the Non-Storing example travels through the root and takes four or more hops. That detour is why the scenario treats the point-to-point requirement as more important than the small header overhead.

The decision: Use Storing mode here. It keeps the latency-sensitive nurse-call traffic off an avoidable root detour, and the scenario’s mains-powered sensors can carry the stated 50—100 bytes of routing state. The resulting choice also avoids concentrating the 120 daily point-to-point events at the root.

Real-World Gotcha: Engineer initially chose Non-Storing (“saves memory!”) but discovered nurse call latency increased from 200ms to 800ms because packets routed through root on different floor. After complaints from nursing staff, switched to Storing mode.

Key lesson: Non-Storing is not universally better merely because it uses less node memory. A network dominated by many-to-one traffic may suit Non-Storing mode, but significant point-to-point traffic gives Storing mode a reason to keep downward state in the network. For a mixed workload, the latency requirement and the actual packet path must settle the choice. Carry that test into the remaining questions: identify the traffic direction first, then locate the routing state, and only then compare cost and latency.