## 8 Performance Comparison  
In order to compare the performance of different schemes discussed in this paper, it is necessary to have complete details of the algorithms proposed for all the schemes. One parameter that can be used to judge the performance of networks is control overhead, but in order to calculate this, it is necessary to know the exact type and size of data that the OBU will be handling. This can only be obtained after finalizing the type of applications that will be deployed in VANETs. Similarly, bandwidth utilization is another important parameter that has to be taken into account, but it is difficult to calculate it as the type of data and applications in VANETs have not been finalized. Therefore, we have compared the major performance characteristics of the discussed schemes by defining or modifying some parameters in Table 1 and we have discussed the major features and disadvantages of each scheme in Table 2. For comparison of the schemes discussed, we have used the rating system of HIGH, MED, and LOW in Table 1. The performance metrics used in Table 1 are described below:* **Scalability:** Scalability is a well-defined performance metric for network protocols and architectures and it means how well a system can cope with the expansion of the network while maintaining the performance standards. A LOW in this category means that the scheme is not suitable for a network in which the number of nodes can grow beyond a small number. A MED in this category means that the scheme can work well for a limited number of nodes but it should not exceed that limit. A HIGH means that the scheme is highly scalable and can work well for a very large number of nodes. * **Computing cost:** The computing cost has been chosen as a metric because it is always in demand and usually it is always less than what is desired. Furthermore, experience has shown that the appetite of programs and data eats up the computing power available very quickly. We have considered the computing cost at both the RSU and OBU. This metric is especially important at the OBU end where we can have reasonable, but never excessive, computing power. A LOW here means that the computing resources required are much less than available. HIGH means that computing resources available might fall short of what is required. MED means that the computation resources are sufficient. * **Privacy:** This is the fundamental requirement of all schemes studied and has been rated according to the merits and demerits of each when viewed in its entirety, e.g., in the case of pseudonym _cum_ PKI schemes, the privacy has been rated as MED as the PNs changing and their maintenance poses a serious challenge for the successful deployment in VANETs. HIGH means strong, MED means acceptable but risky, and LOW means unacceptable or no level of privacy. * **Latency:** This is another well-known parameter for networks that means delays which are experienced in a network due to any reason. A network with LOW latency is considered to be fast and vice versa. * **Cost of deployment:** This parameter indicates whether the infrastructure requirements make it easy to deploy in the practical world or not. A scheme with HIGH cost of deployment is obviously high-cost and difficult to deploy, _i.e._, with many additions/changes to the existing network making it impractical. A scheme which gets a LOW in this metric will be low-cost to deploy and will require a few changes to the existing network to make it feasible.