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Vanet routing
- 1. (ieee transactions on vehicular technology, vol. 58, no. 7, september 2009
- 2. VANET A subclass of Mobile Ad hoc networks. Uses vehicular traffic as its nodes. Allows high node mobility. Takes advantage of restricted paths (Roads).
- 3. Limitations of MANET[1]: • Inefficient mobile node handling. • Leads to frequent makings and breakings of path between source and destination.
- 4. Geographical Routing: May got failed in case of dead ends. Inefficient Route Selection
- 5. RBVT Every node is equipped with- 1) GPS Transceiver 2) Digital Maps 3) 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.
- 6. RBVT-R: A Reactive Protocol Creates 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
- 7. 1. Route Discovery Source floods an RD packet. Uses improved flooding mechanism. RD Packet gets updated with the identities [Ij] of Intersections.
- 8. 2. Route Reply Destination node generates RR packet. Data in RD is copied to RR. RR reaches source through the same path After receiving RR, source transmits data packets.
- 9. 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.
- 10. RBVT-P : A proactive protocol Periodically 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 Discovery 2) Topology Dissemination 3) Route Computation 4) Route Maintenance
- 11. 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 generator Endpoints of traversed segments are stored in CP CP returns back to its generator with neteork topology info.
- 12. 2. Topology Dissemination Topology info from CP is copied to RU packets. Old routing table at nodes are updated by new RU content. Routing tables are updated in segment by segment basis.
- 13. 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.
- 14. 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.
- 15. 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
- 16. Continue… •RTS is sent •CTS by n2 •DATA by nS •ACK by n2
- 17. 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.
- 18. 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.
Editor's Notes
- Good after noon to one and all. Today I am going to discuss about Vanet routing in city roads using real time vehicular traffic information. This is the paper that was submitted in September of 2009. Now, let me explain it in brief.
- Vanets are a sub class of mobile ad hoc networks which uses vehicles to transmit data. The main difference between these mobile ad hoc networks and vehicular ad hoc networks is that – In VANETs, node mobility is restricted to only the predefined paths – nothing but roads. Moreover, VANETs support a very high node mobility. Whereas, In MANETs node mobility is not restricted to specific paths.
- But, the MANET protocols cannot give a satisfactory output with the high mobile nodes like vehicles. Highly mobile nodes lead to the frequent making and breaking of the routes. Because, For example, If this is the source. And this is the destination. The traditional protocols of MANET will identify the best route present. The whole route information is stored in the header of the packets being transmitted. Now, if the mobile node moves from its position to the position of A – Then the route must be reconstructed by removing Io in the header of the packet. This frequent making and breaking of routes lead to unnecessary overhead.
- To overcome these drawbacks of MANETs, one other alternative is the usage of Geographical Routing. In this routing, data is transmitted b/w source and destination without any formation of route between them. Data is transferred from source to destination in the form of packets through the node present in between them. In this protocol, any node that ensures progress towards destination can be used for forwarding. But, the main drawbacks are, Geographical routing may route packets towards dead ends. As shown here, in order to transfer packets from source to destination, GR protocols may use Node like n1 and n2. This may lead to unwanted traffic overhead. And sometimes, this GR protocols cannot handle the high mobile nodes. Also, as shown here, geographical routing may chose the weaker paths. Here, in this case, probability of path breakage is more.
- So, this paper has put forward – the two protocols called as RBVT protocols, for the efficient data transfer using mobile nodes. These RBVT protocols requres that, every node is equpped with a GPS Transceiver, Digital Maps Those two protocols are nothing but – RBVT –R : A reactive protocol RBVT –P : A pro active protocol
- Now, let me discuss about RBVT reactive protocol. This protocol creates road based paths by using CONNECTED road segments. Here the connected road segments are nothing but, road between two intersections with a sufficient traffic density. And the information about the route from source to destination is stored in the header of the data packets. And this routing is done in three steps. Route Discovery Route Reply Route Maintenance.
- When source S needs to transmit data to destination D. First of all, a route discovery packet is broadcasted by source ,S . All the nodes surrounding S receives this RD packet. As soon as the RD packet is received- it will not be rebroadcasted immediately. For example, RD packet broadcasted by S is received by A and B. Then these nodes will retain that packet with them for a certain period of time – called asTTL. TTL is inversely proportional to its distance from the source. If once the TTl expires , then that node will rebroadcast the RD packet. That means, farthest node will get an opportunity to rebroadcast first. And if the same RD packet is received for second time by a node – then it will not rebroadcast the packet with it.. Hence, farthest node will get an opportunity to forward data. By following the similar process, RD packet reaches destination as shown here.
- Once the destination receives RD packet, Destination generates RR packet. The routing information present in the RD packet will be copied to the RR packet. This RR packet will be sent back to the source following the same path. As soon as the source receives the RR packet, then it starts transmitting data through this path. =============================================================================== If the destination receives more than 1 RD packets, then it will compute the best route. But most probably, first one will be the best. Because, it is the one which has transmitted RD packet more faster than the remaining.
- As RR is received by the source, source starts transmitting data to destination. It stores the routing information in the header of the data packet. But as the vehicular nodes are mobile – sometimes source may move from its initial position to this position. Then, in that case identity of I1 should be removed from the headers of data packets. This is accomplished by using route update packets. These will be transmitted between source and destination just like RD packets. Sometimes some road segments get sparsely populated by the nodes. And a node in that segment may not be able to send data to the next intersection. Then in that case, RE packet will be generated by that node and it will be sent back to the source. Then source will find an alternate route.
- Now, let me discuss RBVT- proactive protocols. This protocol periodically computes the real time graph of connected road segments. It assumes that source can use location based queries to know the position of destination. Then, using graphs of network topologies present in the nodes, source computes the shortest path for transmission and sends the data packets. Here in this protocol, routing is done in 4 steps. Topology discovery Topology Dissemination Route computation Route Maintenance
- Fist of all, a few nodes in the network transmits connectivity packets into the network. Nodes decide themselves to transmit packets independently depending on the last update received by them, estimated number of nodes in the network by historic hourly traffic information. The perimeter to be traversed by the nodes is defined by the CP generator itself. When a Connectivity packet is traversed through a segment, then the end points of the segment are stored accordingly in the CP stack. As shown in the figure CP generated by G traverses through the connected segments and returns back to the generator with network topology information.
- The network topology information in CP is copied to route update packets. These route update packets are brodcasted into the networks. And the remaining nodes update their routing table with the data present in RU packets. When a node receives a new RU packet, then it will replace its routing table completely with content in new RU table. Instead of that, it updates the content in that in segment by segment basis – as the perimeter of all connectivity packets are not same.
- Now, all the nodes will be continuously get updated by RU packets. Now if a node wants to send a packet to destination, it computes the best route available by obtaining the location of Destination using location based queries. And the routing information is stored in the header of the da
- Inorder to maintain the clear info about the surrounding nodes, nodes usually transmit the continuous beaconing hello msgs. But these continuous hello message creates heavy conjestion in the network. So to overcome this problem, this these guys used RTS/CTS mects mechanism to overcome this problem. So
- Hence, we can conclude that, RBVT-R and RBVT-P are the 2 efficient protocols which has outperformed the traditional protocols of MANET. Simulation results in the urban setting has shown that, RBVT-R best in terms of average delivery rate and RBVT-P has performed best in terms of average delay.