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

5

6

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