# A Routing Algorithm Based on Real-Time Information Traffic in Sparse Environment for VANETs
## 3 Effective Information Traffic
### Effective Information Traffic  
We will use an example in Figure 2 to illustrate our motivation to introduce effective information traffic. Consider Figure 2, where node \(S1\) intends to send packet to node \(D1\). It is clear that there is an optimal routing path through node \(d\), \(P=\{S1,a,b,c,d,g,h,i,j,k,l,m,n,o,D1\}\). This routing path will provide the best network performance, such as end-to-end delay and delivery ratio. In GPSR, when the packet is sent to node \(d\), it will calculate the distance between neighbors and \(D1\) to select the nearest node to the \(D1\). Since delay selection only depends on the location information, it mostly tends to select node \(e\) as the next hop which leads the packet to the topology hole. The routing path will be created as \(P=\{e,f,e,d\}\) after node d send packet to \(e\) in GPSR mode. Redundant path \(P=\{e,f,e,d\}\) increases the number of hops which is the main factor affecting end-to-end delay. Additionally, a higher number of hops will increase the packet loss rate while topology changes due to the mobility of vehicles. The traditional solution is traffic-aware which uses RSU or broadcast to get the vehicle density of the road segment and then select the segment with higher vehicle density for transmission. However, there are two drawbacks in this approach: (1) additional network consumption, like RSU device and overhead for broadcast; (2) it is not suitable for a sparse network to express the link degree by vehicle density. Because it is very likely that the vehicles will gather together and cause the node density of this road high while the network hole still exists. In some cases, the same vehicle density may lead to different connectivity results. In this paper, we introduce a novel concept called effective information traffic to solve this problem. By analyzing the node connectivity of Formula (1) and the simple instance in Figure 2, we can get the conclusion that the central nodes have better connectivity than edge nodes. From Figure 2, routing redundancy can be avoided by using the central nodes as the relay node, such as node \(g\). However, in practical application, we can not use the node connectivity defined by Formula (1) to compare which is the best relay node in the neighbors. The reason is that the global topology is  
Figure 2: Forwarding example. unknowable. Each forwarding node can only get the location of the current node and destination node. If the method of the broadcast is used to obtain the location and connection information of all nodes, there will be a lot of network resource consumption. It is unwise to design a protocol that uses this method because of the frequent topology changes. Therefore, we propose to use effective information traffic to replace the node connectivity defined in (1). The effective information traffic can be described as: the amount of data effectively forwarded by a node in a certain time \(t\). Effectively forwarding denotes a successful forwarding process including receiving and sending to the best relay node. Correspondingly, invalid information traffic is described as the information traffic in recovery mode. For instance, while routing path \(P=\{S1,a,b,c,d,g,h,I,j,k,l,m,n,o,D1\}\) is creating, all of the nodes in the path get a higher effective information traffic which leads to the situation that packet is sent to the central nodes rather than edge nodes. If the packet is sent to edge nodes like node e, the forwarding mode mostly inter to recovery mode at the node of \(f\) because there is no node closer than node \(f\) to the destination. In this situation, although the effective information traffic of nodes in path \(P=[d,e,f]\) increase, the transmission process on the path \(p=[f,e,d]\) is considered as invalid transmission, which will take time but can not let EIT increases. In this mechanism, the node with high EIT will be more competitive in the relay selection.