Vanet routing

Vanet Routing on city roads using Real time

Vehicular traffic Information(ieee transactions on vehicular technology, vol. 58, no. 7, september 2009)

VANET A subclass of Mobile Ad hoc networks.

Uses vehicular traffic as its nodes.

Allows high node mobility.

Takes advantage of restricted paths

(Roads).

Limitations of MANET[1]:• Inefficient mobile node handling.• Leads to frequent makings and

breakings of path between source and destination.

Geographical Routing:May got failed in case of dead ends.

Inefficient Route Selection

RBVTEvery node is equipped with-

1) GPS Transceiver2) Digital Maps3) A Navigation System

RBVT Protocols:

1. RBVT-R – A reactive protocol

2. PBVT-P – A pro active protocol

– Road based using vehicular traffic Information protocols.

RBVT-R: A Reactive ProtocolCreates road based paths by using

connected road segments.Information about the route is

stored in the header of the packet.

Routing is done in 3 steps: 1) Route Discovery 2) Route Reply

3) Route Maintenance

1. Route DiscoverySource floods an RD packet.Uses improved flooding

mechanism.RD Packet gets updated with the identities [Ij] of

Intersections.

2. Route ReplyDestination node generates RR

packet.Data in RD is copied to RR.RR reaches source through the

same pathAfter receiving RR, source transmits data packets.

3. Route Maintenance

Route once generated cannot be the same forever.

RU packets are used to update routes.

RE packets are uni-casted back to source if any intersection

is unreachable. Only after few REs, RD packets are generated by source.

RBVT-P : A proactive protocolPeriodically computes real time graph of connected road segments.

Maintains consistent view of network connectivity at each node.

Source uses location based queries to find destination’s location.

Routing is done in 4 steps:1) Topology Discovery2) Topology Dissemination3) Route Computation4) Route Maintenance

1. Topology Discovery

CPs are unicasted in the network.A Node decides to transmit CP or

not - by itself independently.CP operates in a limited perimeter –

decided by its generatorEndpoints of traversed segments are stored in CPCP returns back to its generator with neteork topology info.

2. Topology DisseminationTopology info from CP is copied to

RU packets.Old routing table at nodes are

updated by new RU content.Routing tables areupdated in segment by segment basis.

3. Route Computation

Source node computes the shortest path.

Series of intersections representing path are stored in header.

Timestamp is also included for freshness comparison.

4. Route Maintenance

Header of data packets are updated with fresher information by intermediate nodes.

In case of any route break, auto transition to geographical routing takes place.

When packet reaches a node that has fresher information, then it switches back to RBVT-P.

Forwarding Optimization

Beaconing “Hello” messages in GR reduces overall end-end performance

But is important for maintaining accurate list of surrounding nodes

To overcome this IEEE 802.11 RTS/CTS mechanism is extended where next hop is self elected by receiver itself

Continue…

•RTS is sent

•CTS by n2

•DATA by nS

•ACK by n2

Conclusion:RBVT –R and RBVT-P are the two

efficient protocols to handle highly mobile vehicular nodes.

RBVT-R : best average delivery rate [2]

RBVT-P : Least average delay.

References:[1] Elizabeth M. R. and Chai-Keong

T.,,”A review of current routing protocols for ad hoc mobile wireless networks”, Technical report, University of California and eorgia Institute of Technology, USA, 1999

[2] Josiane Nzouonta, Neeraj Rajgure, Guiling Wang and Cristian Borcea, ” VANET Routing on City Roads Using Real-Time Vehicular Traffic Information”, IEEE Transactions on Vehicular Technology, Vol. 58, No. 7, pp. 3609-3626, September 2009.