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

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)

RPL Operation

2 DIO DIO 1 0 DIO 1 DIO 2 DIO 1 DIO DIO DIO 2 2 3 3 3 3 • • 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

RPL Fine Tuning for VANETs

• • Timer fine-tuning: – – Immediate ETX probing for a new neighbor Immediate broadcasting DIO election msg upon new parent – Immediate broadcasting DAO election msg upon new parent 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

Loop Avoidance and Detection

Qualnet Evaluation Setup

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

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

ETX Probe Period on PDR

• The packet delivery ratio decreases as ETX probe interval increases -- delayed response to changing topology

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

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

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

Modified RPL Improvement

• • PDR before and after changes The improvement is about 20%

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