A Comprehensive Evaluation of RPL under MobilityKevin 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

IntroductionTraffic offloading from 3G to WiFi AP to save moneyMultihop-to-infrastructure WiFi access reduces the number of AP deploymentsIntuitively, tree structure is formed with root of the tree at the APConsider Routing Protocol for Low power and lossy networks (RPL)

What About Other Ad Hoc Routing?Reactive routing protocols are susceptible to route breaksLink state routing protocols unscalable because of flooding global topology information

RPL Operation01132221DIODIODIODIODIODIODIODIODIODIODIODIODIODIO233332Directed Acyclic Graph (DAG) Information Option (DIO) messages are broadcast to build the tree; includes a nodes rank (its level), ETX, etc.ETX probe is sent periodically to probe neighboring ETX

RPL SummaryRPL forms a Destination Oriented Directed Acyclic Graph (DODAG), with the root of the tree being the APDODAG minimizes the cost to the root per Objective Function; used ETX hereDirected Acyclic Graph (DAG) Information Option (DIO) messages are broadcast to build the tree; includes a nodes rank (its level), ETX, etc.A node selects a parent based on the received DIO msgs and calculates its rankDestination Advertisement Option (DAO) msg sent periodically to notify parent about routes to downward nodes

RPL Fine Tuning for VANETsTimer fine-tuning:Immediate ETX probing for a new neighborImmediate broadcasting DIO msg upon new parent electionImmediate broadcasting DAO msg upon new parent electionLoop avoidance and detection: Stamp DIO msg with parents ID; If a node that receives the DIO msg is equal to the parents ID in the DIO msg, itll discard the DIO msg

Loop Avoidance and Detection

Qualnet Evaluation SetupLillian Dai, Sateesh, Raghu, Kevin LeeAP5000m2500m25mph, 45mph, 65mphPacket delivery ratio (PDR) and overhead are obtained with varied DIO msg period and ETX probe periodCar 1Car 2Car 3Car 7

Lillian Dai, Sateesh, Raghu, Kevin Lee

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

ETX Probe Period on PDRThe packet delivery ratio decreases as ETX probe interval increases -- delayed response to changing topology

ETX Probe Period on OverheadAs the probe period increases, the number of ETX probes decreasesPDR 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 PDRPDR drops as DIO msg period increasesPDR drops as speed increases for a given DIO msg periodDiminishing return with decreasing DIO msg period suggests trickle

The lower the DIO msg period, the higher the DIO msg overheadDIO Msg Period and Speed on OverheadDIO msg overhead increases with increasing speed

PDR before and after changesThe improvement is about 20%Modified RPL Improvement

ConclusionStudied the impact of DIO msg period and ETX probe period on PDR and overhead => Show the value and advantage of trickle timerFine tune RPL and improve its performance in vehicular networks by 20%Future work: More complex sim. scenarioConsider speed and direction in forming a treeConsider trickle timer for ETX probe period

* Wireless service providers such as AT&T and Verizon have changed from a fixed monthly fee to a tiered or per bit pricing structure for data usage. As free WiFi networks become more accessible from vehicles, users will have a strong economic incentive to opportunistically offload data traffic from 3G and 4G links to free WiFi links.* Since WiFi deployment is not prevalent, enabling vehicles to access roadside WiFi through other vehicles (multihop-to-infrastructure) allowmore vehicles to take advantage of data offloading.*A node selects a parent based on the received DIO msgs and calculates its rank: Lets say a node receives 3 DIOs from three neighbors. It will consider neighbors whose rank is less than its own. Based on its link etx to each node and their respective ETX to the root, the node can establish ETX using either of the two nodes. The node can then determine who its parent is.

***10-node caravan traversing a 5000m-long road Inter-node distance is maintained at 250mTraces of 25mph, 45mph, and 65mphTwo-way CBR traffic are sent from any car of the caravan

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