Tonghong Li, Yuanzhen Li, and Jianxin Liao Department of Computer Science Technical University of Madrid, Spain Beijing University of Posts & Telecommunications Beijing, China IEEE ICDCSw, 2009 A Contention-Based Routing Protocol for Vehicular Ad Hoc Networks in City Environments /10/13 Speaker: I-Hsin Liu

Outline Introduction Contention Based Routing Protocol (CBRP) Simulation Conclusion 2

Introduction VANETs can be roughly classified in two categories: Broadcasting the information from the vehicle to all surrounding vehicles. Most safety applications such as accident alerts. Delivering the information to a particular destination through multi-hop. 3

Introduction This paper proposes a contention based routing protocol for VANETs in city environments. Different from the position based routing, this protocol does not require the node to maintain its neighbors’ locations. 4

Goal This paper proposes a contention based routing protocol for VANETs in city environments. The goal of paper is Increasing delivery ratio Decreasing end-to-end delay 5

Overview CBRP works in two modes: Street mode. Junction mode. 6

Overview When a packet is carried by a vehicle in a street, CBRP operates in street mode. Using contention based forwarding to deliver the packet greedily to the next junction. When a packet is in the junction area, CBRP operates in junction mode. It first performs junction selection in order to determine the next junction. 7

Overview 8 Destination Street Mode Junction Mode Junction Mode

Assumption We assume that each vehicle is equipped with a navigation system and a GPS receiver. Position. Moving direction. In every navigation system, there is a digital city map. real traffic network. Each node know the position of destination. Each node know the ID of destination. Destination is fixed. 9

Contention Based Routing Protocol 10 Data forwarding in street mode Junction selection Data forwarding in junction mode Junction selection Data forwarding in junction mode

Junction Selection Every packet includes in the packet header. The ID and position of the node that has just forwarded the packet. Previous junction (PJ) Current junction (CJ) Source ID Source’s position Destination ID Destination’s position Packet ID 11 Destination Current junction Previous junction

Junction Selection When is junction selection performed? Case 1: when a packet is sent by the source node. Case 2:when a node goes from street mode to junction mode. In order to aid junction selection, a weight is assigned to each street based on its traffic density. i.e. more vehicles, less weights assigned. 12

Junction Selection A path can be computed by using Dijkstra’s least- weight path algorithm. Case 1:from the source to the destination. Case 2:from the CJ to the destination. We choose the first junction in the Dijkstra’s least-weight path as the new CJ. 13 C C D D E E Destination Source Node CJ PJ C C

Contention Based Routing Protocol 14 Data forwarding in street mode Data forwarding in junction mode Junction selection Data forwarding in junction mode Junction selection

Data forwarding in street mode A node that receives a packet at first time. determines whether or not it is a candidate next hop of Previous hop(Phop). Nodes in the shaded area are candidate next hops of Phop, since they are closer to CJ than Phop. 15

Data forwarding in street mode 16 Destination PJ Street Mode CJ Shaded Area A B S

Data forwarding in street mode Note that if a node is in shaded area and does not move towards CJ. We do not classify it as a candidate next hop even though it is in the shaded area. 17 PJ Street Mode I3 Shaded Area CJ A S Destination Junction Mode

Data forwarding in street mode Note that if a node is in CJ’s junction area and does not move towards CJ. We do not classify it as a candidate next hop even though it is in the shaded area. 18 PJ Street Mode I3 Shaded Area CJ A S Junction Mode Destination CJPJ Discard the packet

Data forwarding in street mode After classifying itself as a non candidate next hop, a node discards the packet immediately. Otherwise, it waits for a delay period before making a decision whether to rebroadcast a packet or not. 19

Data forwarding in street mode The delay of a node is calculated based on the progress it provides towards the packet’s CJ. The packet progress of a node i is defined as P i =dist(Phop, CJ)-dis(i, CJ) 20 maximum forwarding delay. radio range. Destination Street Mode CJ dist(Phop, CJ) dis(A, CJ) Phop A

Data forwarding in street mode During the delay period, the node listens to other retransmission of the same packet. If the node receives the same broadcast from other node closer to CJ than itself in the delay time, it drops the packet. Otherwise, the node forwards the packet at the end of the delay period. Avoid sending duplicates. 21

Data forwarding in street mode If no further rebroadcasts happen during τ period it means that no next hop neighbors are currently present due to the partitioned network. In this circumstance, Phop holds the packet in its buffer. repeats the broadcast after waiting t time. The process is repeated until the next hop neighbor appears. 22

Data forwarding in street mode In this case, we can set t as follows: assume that Phop’s current speed is V the maximum speed in the street between CJ and PJ is max V. 23 Destination Street Mode CJ Phop V PJ V max

Data forwarding in street mode The idea behind the choice of t is: (1) the packet can not be rebroadcasted too often, which will jam the network. (2) t can not be set too large, as it will miss the opportunity to forward the buffered packet further. 24

Simulation 25

Simulation 26 Position Based Routing Protocol

Simulation 27

Simulation 28

Conclusion In this paper, we present a contention-based routing protocol designed specifically for vehicular networks in city environments. This protocol does not require the node to maintain its neighbors’ locations. 29

30 Thank You