rpl
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A Comprehensive A Comprehensive Evaluation of RPL Evaluation of RPL under Mobilityunder 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 Operation0
1 1
3
2
22
1DIODIO
DIO
DIO
DIO
DIODIO DIO
DIODIO
DIODIODIO
DIO
2
3 3 3
3
2
• 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 msg upon new parent
election– Immediate broadcasting DAO msg 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
Loop Avoidance and Detection
Qualnet Evaluation Setup
Lillian Dai, Sateesh, Raghu, Kevin Lee
AP
5000m
2500m
25mph, 45mph, 65mph
Packet delivery ratio (PDR) and overhead are obtained with varied DIO msg period and ETX probe period
Car 1Car 2Car 3Car 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
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
• The lower the DIO msg period, the higher the DIO msg overhead
DIO Msg Period and Speed on Overhead
• DIO msg overhead increases with increasing speed
• PDR before and after changes• The improvement is about 20%
Modified RPL Improvement
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
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