Nizar Alsharif BBCR-VANETs/DTN subgroup meeting 17-Feb....
Transcript of Nizar Alsharif BBCR-VANETs/DTN subgroup meeting 17-Feb....
Nizar Alsharif BBCR-VANETs/DTN subgroup meeting 17-Feb. 2012
Overview… VANETs (What & why?)
Safety ITS services Sensor network? MANETs?
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Infotainment and interactive apps
Chatting Gaming File download Internet surfing
VANETs Routing
Outline
PBR Introduction
Some PBR concepts
GyTAR
PBR limitations
Summary
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Taxonomy of Various Routing Protocols in VANETs
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Position-Based Routing (PBR):
Depends on location information about the destination and neighboring vehicles.
PBR Components:
S A
D
Closest to D
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Some Concepts..
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Anchor-based and hop-by-hop routing
Forwarding Strategy
e.g., A-STAR vs. GPSR
Anchor
dS
dB
Source routing and distributed routing
e.g., GSR vs. GPSR
Hybrid (update on-the-fly e.g., DSR)
Some Concepts.. (cont'd)
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Static Info-based Route Planning Info examples: map info,
bus routes, road width e.g., A-STAR, MDDV
Statistic Info-based Route Planning Info examples: statistical traffic
density info. e.g., VADD
Real-time Info-based Route Planning Info examples: Traffic awareness
e.g., GyTAR
M. Jerbi, S.-M. Senouci, T. Rasheed, Y. M. Ghamri-Doudane, Towards efficient geographic routing in urban vehicular networks, IEEE Transactions on Vehicular Technology 58, 2009, pp. 5048-5059
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GyTAR
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Improved greedy traffic-aware routing protocol (GyTAR) Position-based routing
Anchor-based routing (intersections)
Distributed routing
Real-time info-based routing
GyTAR.. (cont'd) How does it work? (Forwarding Strategy)
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Next Junction Selection: Routing decisions are taken at junctions
Each adjacent junction is given a score:
Curvemetric distance Vehicle Density at road segment
Between two junctions
Improved greedy routing Greedy with neighbour location
prediction
GyTAR.. (cont'd) How does it work? (Forwarding Strategy)
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Junction Score Calculations:
Comments on GyTAR
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It outperforms static and statistics-info-based routing protocols
It Suffers from the location service problem
It suffers from the local vehicle traffic awareness problem (limited topology vision)
Case 1: I2I3 : Higher delivery latency
Case 2: I2I6I7 : Higher delivery latency
Case 3: I2I6I2 : Packet pouncing!
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Some PBR Limitations
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1] Location Service Relying on another network: e.g.,
cellular, sense network..etc Cost Cooperation issues
Flooding-based LS Scalability Performance degradation
Quorum-based LS Scalability Performance degradation
Use of gateways and location servers
Simulation Time 50 Sec
Map Size 7km x 7 km
Number of vehicles 4700 vehicles
Vehicle Density Free flow (~6 v/lane/km)
Number of RSUs 2
Maximum vehicle Velocity 60 km/h
Transmission Range 250 m
Routing Protocol GPSR
Beacon Interval 250 ms
Location Update Interval 2000 ms
Location Req. Interval 500 ms
Data Packet lifetime 500 ms
Simple Infrastructure-based LS Nodes periodically report (unicast) their
positions to the nearest gateway (RSU) Sources send location query messages to
closest RSU If destination location has not received, resend
the query message
Some PBR Limitations.. (cont'd)
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1] Location Service (cnt’d)
Delivered Data Packets Lost Packets Due to Routing Failure
Assuming the availability of destination location
64% 36%
Delivered Data Packets
Lost Packets Due to Routing Failure and Delay of LS
Lost Due To LS Failure
29%
28%
43%
0
100
200
300
400
500
600
GPSR w/o LS GPSR with LS
Avg. E2E Delay (ms)
Avg. Buffering Delay (ms)
Some PBR Limitations.. (cont'd)
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2] Trajectory selection (route planning) Due to the limited topology vision, PBR might:
Misguide packets to dead-ends (e.g., A-STAR with low density)
Take longer paths (e.g., GPSR with perimeter routing)
Cause packet loss (e.g., GyTAR in packet bouncing case)
3] Next-hop selection in anchor-based routing
Is Greedy the best option? Is the node still in
communication range? Signal quality?
Some PBR Limitations.. (cont'd)
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Recovery procedure causes extra delay Perimeter routing can
encounter huge number of intermediate hops
Carry-and-Forward adds huge E2E delay
Others? Recovery procedure should be
minimized
5] Unreachability problem 4] Designing a recovery strategy How to deal with unreachable vehicles
Source, destination, and location agent isolation
OBU is off Vehicle has moved away
from the reported location
Current solutions: Re-route? Buffering?
Some PBR Limitations.. (cont'd)
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Real-time info-based protocols performs well
What are the information? Vehicle Traffic? Data traffic?..etc
How to deploy the information?
How to disseminate the information?
6] Using Real-time information 7] PBR security
Primary security requirements Routing attacks Position verification problem Delay for cryptographic operations
8] Privacy
Announcing current location and responding to location queries disclose users identity and location privacy
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Summary and Conclusions
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Anchor-based and hop-by-hop routing
Source routing and distributed routing
Offline information based routing and real-time information based routing
Due to its superiority, many recent VANETs routing protocols deploy PBR approach
Issues.. How to efficiently determine the
current destination location ? Scalability Delay
How to design efficient forwarding strategy Next anchor selection Next hop selection Minimizing recovery
procedure How to design efficient recovery
strategy
Summary and Conclusions.. (Cont’d)
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Issues..(Cont’d)
How to collect and utilize real-time information
Other challenges
Unreachability Security Privacy
…The end