1. The ETX Objective Function draft-gnawali-roll-etxof-00 ROLL WG IETF 77 - Anaheim, CA 3/22/2010 Omprakash Gnawali and Philip Levis Stanford University

2. RPL and Objective Functions Objective functions are used to select next hop among candidate next hops Examples – Hop count (OF0) – Throughput – ETX Combinations possible

3. The ETX Metric ETX = Expected Number of Transmissions – Includes ReTX and ACK Path ETX = Sum of Link ETX Link ETX described in draft-ietf-roll- routing-metrics Many ways to compute ETX Widely used in wireless routing – Several MANET protocols, CTP

4. The ETX Objective Function (ETXOF) Pick the candidate with the smallest Path ETX – Path ETX = 0 at DAG root – Path ETX = Link ETX to a candidate n + Path ETX from n to the DAG root Some considerations – Frequency of updates – Hysteresis to prevent excessive churn – Path and link ETX thresholds – Tie-breaker

5. RPL and ETXOF ETXOF applicable to many RPL deployments Adopt draft-gnawali-roll-etxof as a WG document?