A Comprehensive Evaluation of RPL under Mobility

1. A Comprehensive Evaluation of RPL under Mobility Kevin Lee, Raghuram Sudhaakar, Jianxia Ning, Lillian Dai, Sateesh Addepalli, Flavio Bonomi * Paper accepted by Consumer Communications And Networking Conference (CCNC 2012) Special Session Information Dissemination in Vehicular Networks * Extended paper submitted to Focus Issue on Vehicular Ad-hoc Networks in International Journal of Vehicular Technology in February 2012

2. Introduction • Traffic offloading from 3G to WiFi AP to save money • Multihop-to-infrastructure WiFi access reduces the number of AP deployments • Intuitively, tree structure is formed with root of the tree at the AP • Consider Routing Protocol for Low power and lossy networks (RPL)

3. RPL Operation • Directed Acyclic Graph (DAG) Information Option (DIO) messages are broadcast to build the tree; includes a node’s rank (its level), ETX, etc. • ETX probe is sent periodically to probe neighboring ETX DIO 0 1 DIO DIO DIO DIO 2 DIO 1 DIO 1 2 DIO DIO DIO DIO DIO 3 2 2 DIO 2 DIO 3 3 3 3

4. RPL Fine Tuning for VANETs • Timer fine-tuning: • Immediate ETX probing for a new neighbor • Immediate broadcasting DIOmsg upon new parent election • Immediate broadcasting DAOmsg upon new parent election • Loop avoidance and detection: • Stamp DIO msg with parent’s ID; • If a node that receives the DIO msg is equal to the parent’s ID in the DIO msg, it’ll discard the DIO msg

5. Loop Avoidance and Detection

6. Qualnet Evaluation Setup AP 2500m Car 7 Car 3 Car 2 Car 1 25mph, 45mph, 65mph 5000m Packet delivery ratio (PDR) and overhead are obtained with varied DIO msg period and ETX probe period Lillian Dai, Sateesh, Raghu, Kevin Lee

7. Rank Change & Duration wrt Time and Speed • Lead car (Car 1) establishes conn @ 199s/79s @ 25mph/65mph • Rank duration is 22s for 25mph and 9s for 65mph 25mph 65mph

8. ETX Probe Period on PDR • The packet delivery ratio decreases as ETX probe interval increases -- delayed response to changing topology

9. ETX Probe Period on Overhead • As the probe period increases, the number of ETX probes decreases • PDR does not degrade as much for ETX probe period 1s, 3s, and 5s => topology change is on the level of 5s granularity => An adaptive timer approach for ETX probe recommended

10. DIO Msg Period and Speed on PDR • PDR drops as DIO msg period increases • PDR drops as speed increases for a given DIO msg period • Diminishing return with decreasing DIO msg period suggests trickle

11. DIO Msg Period and Speed on Overhead • The lower the DIO msg period, the higher the DIO msg overhead • DIO msg overhead increases with increasing speed

12. Modified RPL Improvement • PDR before and after changes • The improvement is about 20%

13. Conclusion • Studied the impact of DIO msg period and ETX probe period on PDR and overhead => Show the value and advantage of trickle timer • Fine tune RPL and improve its performance in vehicular networks by 20% • Future work: • More complex sim. scenario • Consider speed and direction in forming a tree • Consider trickle timer for ETX probe period