ucla engineering computer science robustgeo: a disruption-tolerant geo-routing protocol ruolin fan,...
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UCLA ENGINEERING Computer Science
RobustGeo: a Disruption-Tolerant Geo-routing Protocol
Ruolin Fan, Yu-Ting Yu*, Mario GerlaUCLA, Los Angeles, CA, USA
{ruolinfan, gerla}@cs.ucla.edu*Qualcomm Research, Bridgewater, NJ, USA
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Location-Based Routing
• Greedy Forwarding– Use geographical
locations– Find neighboring nodes
closest to the destination geographically
– Forward the packet to that node S
D
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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
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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
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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
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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 dropped2. TTL exceeded, replicated packet dropped
• If both the original packet and its replica finds a greedy route, one of them is dropped
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Perimeter + Broadcast duplicates
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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
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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
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PERFORMANCE EVALUATION
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Simulation Parameters
• NS3 simulator • Radio channel: OFDM 36Mbps • Propagation Loss Model: Friis • WiFi Standard: 802.11a • Wifi Mac Type: Adhoc Wifi Mac • Transport Protocol: UDP • Application: CBR Client-Server Pair (20Kbps) • Simulation Time: 200s
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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 )
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Simple scenario3 fixed nodes; 2 vehicle clusters (8 nodes)
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Simulated Traffic in DC – Delivery Ratio
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San Francisco Taxi Traces
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Packet Replication: SF Taxi
# Intermittencies # Packets
1 1434
2 1063
3 981
4 214
5 3
6 5
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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)
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Thank You!
Questions?