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