A Road-based QoS-aware Multipath Routing
for Urban Vehicular Ad Hoc Networks
指導教授：王國禎
學生：謝宜玲
國立交通大學資訊科學與工程研究所
行動計算與寬頻網路實驗室
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Outline
• Introduction
• Related work
• Proposed multipath routing protocol for urban
VANETs (MRV)
– Multiple road-disjoint paths discovery
– Path life time and life periods prediction
– Dynamic QoS path switching
• Simulation
• Conclusion
• References
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Introduction – Motivation
• Stable and efficient routing plays a key role for
the success of VANETs
• Road-based routing has been shown wellsuited in urban VANETs [5][8]
– (better than traditional node-based routing)
• Multipath routing provides alternative routes
once the current route fails
However, existing multipath routing protocols
are node-based, which are not suitable for
urban VANETs
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Introduction – Routing in VANETs
• Road-based routing vs. node-based routing
– Node-based routing: sensitive to node mobility
– Road-based routing: depending on node density
• As long as the node density is not sparse in each road
section of a path, the whole path is connected
– Node density does not vary too much in a road section, in a
short period
• It has more choices of next hop
Road-based routing is steadier than node-based
routing, for urban VANETs
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Introduction – Multipath routing
• Multipath routing
– further enhance the route stability
1. provides alternative routes once the current route
fails
2. provides concurrent transmission with multiple
paths (optional)
• Existing multipath routing protocols
– are node-based (not road-based)
– potential drawback: potential transmission
interference if they are multiple paths through the
same road sections [14]
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Introduction – QoS routing
• QoS routing in urban VANETs
– Utilize probability of connectivity and hop count to decide the best
QoS path
– derive/estimate probability of connectivity and hop count with
vehicles mobility data (e.g. speed, position, node density)
• Most of current QoS routing protocols for VANETs are
node-based
– derive a route’s QoS along with route discovery
– only consider straight roads (e.g. highways) or limited local roads
• due to inherited weakness of node-based routing
For generic city road topologies, road-based routing approach is
preferred
• Road-based QoS routing
– IGRP [5]: directly determine a path’s with the assistance of traffic
statistics
• Additional traffic statistics is required; however, it may not reflect the
current situation
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Introduction – the proposed routing protocol
• We propose a road-based QoS-aware multipath
routing protocol for urban VANETs (MRV)
1. MRV can find multiple road-disjoint paths
2. Predict a path’s future lifetime and life periods to
adaptively utilize multiple paths
–
We propose a space-time planar approach to predict
the connectivity of each road section in a path
3. Dynamic QoS path switching
–
dynamically switch to a path that satisfies the packet
delay constraint
•
Packet delay is estimated according to a path’s life periods
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Related work
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Related work
• Expected results
• Contribution of MRV over other road-based routing protocols
– Provide multiple path and consider QoS (vs. RBVT-R)
– On-demand route discovery (vs. IGRP)
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Proposed multipath routing protocol for urban VANETs (MRV)
• Problem description
1. How to find multiple road-disjoint paths?
2. Among the multiple paths, we choose the path with longest
lifetime
How to estimate a road section’s lifetime so as to derive a
path’s lifetime
3. As time elapses, a road section becomes connected or
disconnected
 How to dynamically switch to another path
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Proposed MRV – multipath discovery
• Multipath discovery (route discovery, RD)
– RD packet: [src, dest, seq #, road section list (RS list)]
• generated at source and being flooded out, until reaching destination
– The RS list in an RD packet is updated when the packet
enters a new road section
– RD packet table
• Every node maintains one, to check whether a received RD packet
had been seen
1. Road-disjoint paths
• RD packet with duplicate RS is dropped
• (disregarding the beginning and ending RSs)
• However, duplicate RSs are allowed if not enough multiple paths are
available
2. Loop detection
• e.g. a node in RS3 received an RD packet with RS list [5, 3, 2, 7, 8]
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Proposed MRV – multipath discovery
• Route reply
– For each RD packet, the destination node sends a
route reply (RR) packet to the source node
– Along with the RR packet being relayed among RSs,
the path’s future connectivity prediction is
processed in each RS
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Road section connectivity problem
• Geographical forwarding
– used to relay data packets through a road section
• Every node maintains a neighbor table for choosing next hop
• neighbor table: every node periodically broadcast a HELLO
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Road section connectivity problem
• A potential problem and its solution
– As time elapses, a road section may become connected
or disconnected, due to node mobility
RS life periods prediction path life periods path
switching before disconnection
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Road section connectivity problem – space-time planar approach
We propose a space-time planar approach to formulate and
resolve the road section connectivity problem
– A road section’s life period can be derived
 A path’s life period is then derived
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Path lifetime estimation and QoS path switching
• RS life periods is included in the RR packet
– RR packet piggybacks the relay nodes’ neighbor tables
– The last node in the RS, e.g. node i, calculates RS C1C2’s life periods using the space-time planar approach
– Intersect the derived life periods with the existing life
periods piggybacked in the RR packet (so as to reduce
RR packet size)
• The piggybacked neighbor tables are also removed
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QoS path switching
• The source node may switch to a path which is
connected currently or satisfies delay constraint
– Small gaps may be tolerated because of using carryand-forward
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QoS path switching
• Packet delay di for path i is due to two kinds of delay
– Transmission delay (dp)
– Path disconnection delay (dd)
– di = dp(i) + dd(i)
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QoS path switching
• Transmission delay (dp)
– dij : packet delay through RSij, dij = tp*{2+[(Lij – 2*s)/(Tr/2)]}
• tp is transmission delay of a hop, which is regarded as a constant [8]
– dp(i) = ∑dij, for RSij in path i
• Path disconnection delay (dd)
– dd is the sum of the mean of each disconnection period
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Simulation
• Simulator: QualNet 5.0
• Map: a grid map of 1000m x 1000m with 200m
interval [8]
• Total 200 nodes
• Node mobility trace generator: VanetMobiSim
– node speed: [0m/s, 20m/s]
• Radio range: 275m [8]
• Two-ray ground propagation model [8]
– With NLOS, only nodes in adjacent road sections
are allowed for radio communication
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Simulation
• We expect that MRV will have significant higher packet
delivery rate, shorter packet delay and lower control
overhead than a single-path road-based routing
protocol, RBVT-R, and a traditional multipath routing
protocol, AOMDV
• Expected results
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Conclusion
• We have presented a road-based QoS-aware multipath
routing protocol for urban VANETs (MRV)
• MRV is used to find multiple road-disjoint paths and to
estimate paths' future life periods for QoS path
switching
• A space-time planar approach has been proposed to
predict each road section’s connectivity of a path and
to derive a path’s future lifetime and life periods
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Conclusion
• We expect that MRV will have significant higher packet
delivery rate, shorter packet delay and lower control
overhead than a single-path road-based routing
protocol, RBVT-R, and a traditional multipath routing
protocol, AOMDV
• To the best of our knowledge, there is no road-based
multipath routing protocol in literature
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References
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