# An Effective and Efficient Adaptive Probability Data Dissemination Protocol in VANET
## 3 Effective and Efficient Adaptive Probability Data Dissemination Protocol (EEAPD)
### EEAPD Protocol Description  
The primary idea of EEAPD is shown by using two flow chart diagram presented in Figures 3 and 4. From these figures, the explanation is divided into three phases and is described as follows. Each event-driven message (emergency message) explained in the EEAPD protocol (Figure 5) is distinguished by a special identification whereby this identification includes the source vehicle's identification and message identification, assuming a message's header consist of both broadcasting vehicle identification and its position by GPS. Every node posse's data buffer which is special for kept the received original messages except the redundancy ones. EEAPD checks if the packet received by the vehicle is recognizable or not by considering the packets identification kept in the data buffer. EEAPD has three phases: firstly, if the message is not known (new message) only received message coming in front of vehicle message direction is considered to be spread in the network area, as stated by EEAPD on the other hand, the message (new data packet) is kept in buffer by a name \"\(schedule\)\(for\)\(rebroadcast\)\(=\)\(True\)\" then regard this message as having a special rebroadcasting by considering the waiting timer \"\(W(t)\)\" then immediately trigger. Nevertheless, packet data coming from other direction except in front of it show as the reachability from the message direction, this message given by a name \"\(schedule\)\(for\)\(rebroadcast\)\(=\)\(False\)\". Figure 2: Redundancy ratio vs. number of vehicles. _Data_**2019**, 4, 1  
Figure 3: Receiving procedure of effective and efficient adaptive probability data dissemination protocol (EEAPD). Secondly, the message timer should continue to decrease and when it expires with no duplicated received, the trigger timer will determine if it least time among road segments, if this is the case then the message is broadcasted with probability \"\(P=f(r)\)\". Otherwise, cancel both messages waiting for the timer and rebroadcast decision. Thirdly, when the message is known (not new) its waiting timer period \"\(W(t)\)\" should instantly be canceled and discarded if it is scheduled for rebroadcasting, else it is discarded. In both these phases, the redundancy ratio \"\(r\)\" should be updated at the receiving event. The idea implemented in EEAPD is motivated by different protocol schemes such as S1 PD and SEAD. By considering the number of segments (slots) that are fixed, waiting time can be computed as shown in Equation (2). \[W_{t}=\left[N_{st}\cdot\left(1-\frac{min\big{(}D_{ij},\ R\big{)}}{R}\right) \right]\cdot\delta+\mu delay \tag{2}\]  
such that; \(N_{st}\) is a number of road segments (dynamically selected), \(D_{ij}\) is the respective distance from source node \"\(i\)\" to receiver node \"\(j\)\", \(R\) is mean transmission range and \(\delta\) is estimated \(1\) hop delay consists of medium access delay and propagation delay. For more explanation about this strategy, an example of the system model mechanism is depicted in Figure 6. Assume the source vehicle (S) transmit the emergency accident message about 300 m in  
Figure 4: Rebroadcasting procedure of EEAPD. Figure 5: Event-driven packet format. transmission range. With respect from the source node, all nodes (vehicles) within network area are allocated with different slots. Impact of Roads Segment on Rebroadcast  
In this case, (refer to Figure 6b). when the number of vehicles increases, the redundancy ratio (\(r\)) also increases hence, the probability of rebroadcasting become small. From this concept, it is clearly seen that the decreasing of vehicles' density by giving a greater number of road segments in the transmission range leads to small redundancy ratio and finally the probability of rebroadcasting for suitable nodes increasing. Assuming that the Dalian University of Technology (DUT) map (refer to Figure 7) there are numbers of road segments (slots) within transmission range, each road segments (slots) i.e., one slot having almost 100 m apart to each other (refer to Figure 6).