UCLA ENGINEERING Computer Science RobustGeo: a Disruption-Tolerant Geo-routing Protocol Ruolin Fan, Yu-Ting Yu *, Mario Gerla UCLA, Los Angeles, CA, USA {ruolinfan, * Qualcomm Research, Bridgewater, NJ, USA

UCLA ENGINEERING Computer Science INTRODUCTION

UCLA ENGINEERING Computer Science Location-Based Routing A class of routing algorithms that use locations of forwarding nodes to route packets Scalable: no need for each node to know overall network topology Promising routing method for VANETs – Mercurial network topology – Limited bandwidth

UCLA ENGINEERING Computer Science Location-Based Routing Greedy Forwarding – Use geographical locations – Find neighboring nodes closest to the destination geographically – Forward the packet to that node S D

UCLA ENGINEERING Computer Science Location Based Routing Perimeter Forwarding – Sometimes no immediate closer node to the destination can be found Local maximum encountered – Route around the perimeter S D L.M

UCLA ENGINEERING Computer Science Issues with Location Based Routing Works well for mobile scenarios: VANET routing But, cannot handle temporary topology disruptions: – Complete disconnection, ie partitioned network with no end-to-end routes Cannot be dealt with by traditional geo-routing Perimeter routing fails if net is partitioned – Can be short lived, yet frequent, eg vehicular traffic patterns caused by traffic lights

UCLA ENGINEERING Computer Science Delay-Tolerant Networks (DTN) Originally proposed for networks that experience long disconnections (eg space) Exploit mobility of nodes to physically carry data from the source to the destination (carry- and-forward) DTN delivers data in intermittent networks (eg space), but latency is unacceptable in VANETs Insight: use Replication to alleviate latency

UCLA ENGINEERING Computer Science RobustGeo Combines Geo-routing with DTN routing Greedy-forwarding when possible When local-maximum is hit: – Perimeter forwarding + DTN routing – Controlled packet replication to increase delivery probability

UCLA ENGINEERING Computer Science SYSTEM DESIGN

UCLA ENGINEERING Computer Science Design Overview Geo-routing component – Used under all normal greedy-forwarding scenarios – Can make use of all existing geo-forwarding techniques based on that of GPSR Disruption-tolerance component – Used for resolving local maximum scenarios – Perimeter route a replica of the original packet in case the local maximum is temporary – Broadcast the original packet if intermittency lasts too long

UCLA ENGINEERING Computer Science Perimeter Routing Original packet saved into a buffer called the DTQ (delay-tolerant queue) Perimeter forwarding for the packet replica using the right-hand rule until: 1.Greedy route found, ack returned, DTQ dropped 2.TTL exceeded, replicated packet dropped If both the original packet and its replica finds a greedy route, one of them is dropped

UCLA ENGINEERING Computer Science Perimeter + Broadcast duplicates

UCLA ENGINEERING Computer Science Packet Broadcasting Packets in the DTQ with no previous broadcast are broadcast periodically (every 6 sec) – Explore multiple paths to increase delivery rate – Single-hop broadcasting Node that receives a packet via broadcasting saves it in DTQ and waits for greedy path Broadcasting period of 6 s fits vehicular traffic

UCLA ENGINEERING Computer Science DTQ Scheduling

UCLA ENGINEERING Computer Science ANALYSIS: A LIMIT ON PACKET REPLICATION

UCLA ENGINEERING Computer Science Replication Mechanism Over-replication of packets can congest the network Packets are replicated only once in a local maximum situation – A single packet replica is generated when perimeter routing is attempted – Long recovery time can generate multiple packet replicas due to periodic broadcasting A packet replica originating from a broadcast cannot generate more replicas via broadcasting

UCLA ENGINEERING Computer Science Mathematical Model The total number of replicated packets generated due to intermittencies in the network rep: # replicated packets m: # packets that experience local maximum recovery n: # neighbors that receive the broadcasted packet t: Average local max recovery time π: Broadcasting period of each node P b : Probability a broadcast packet found a path P p Probability a perimeter-routed packet found a path K: Total number of intermittencies

UCLA ENGINEERING Computer Science Graphical Representation for One Packet (m = 1) π = 6; n = 10; P p =0.01; P b = 0.2 Intermittency length t is modeled as a Poisson RV with λ=3

UCLA ENGINEERING Computer Science PERFORMANCE EVALUATION

UCLA ENGINEERING Computer Science Simulation Parameters NS3 simulator Radio channel: OFDM 36Mbps Propagation Loss Model: Friis WiFi Standard: a Wifi Mac Type: Adhoc Wifi Mac Transport Protocol: UDP Application: CBR Client-Server Pair (20Kbps) Simulation Time: 200s

UCLA ENGINEERING Computer Science Comparison set Pure geo-routing: – simply drops packet that it cannot immediately route, Geo-routing with a DTQ: – improves delay tolerance but without packet brcst, replication; similar to GeoDTN+Nav, Geo-routing with controlled flooding, – DTQ can only pass the packet to 5 unique neighbors before dropping (like Epidemic Routing )

UCLA ENGINEERING Computer Science Simple scenario 3 fixed nodes; 2 vehicle clusters (8 nodes)

UCLA ENGINEERING Computer Science Simulated Traffic in DC

UCLA ENGINEERING Computer Science Simulated Traffic in DC – Delivery Ratio

UCLA ENGINEERING Computer Science San Francisco Taxi Traces

UCLA ENGINEERING Computer Science Packet Replication: SF Taxi # Intermittencies # Packets

UCLA ENGINEERING Computer Science CONCLUSION

UCLA ENGINEERING Computer Science Conclusion We designed RobustGeo to withstand network intermittencies common to urban VANETs Takes advantage of both the store-and- forward and replication strategies of DTNs A viable tradeoff between increasing network overhead and packet delivery ratio A hybrid solution that allows for connections in both reliable and intermittent networks (typical VANET attributes)

UCLA ENGINEERING Computer Science Thank You! Questions?