UCLA ENGINEERING Computer Science RobustGeo: a Disruption-Tolerant Geo-routing Protocol Ruolin Fan,...

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

yutingy@qti.qualcomm.com

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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?