— With the increasing demand for secure and high-quality communications in public access wireless IP networks, it is very important to have an in-depth understanding of the relationship between the security and quality of service (QoS). In wireless networks, authentication can provide secure communications by preventing unauthorized usage and negotiating the credentials for data transmission. Nevertheless, it induces heavy overhead and delay to data transmission, further deteriorating overall system performance. Therefore, we analyze the impact of authentication on the security and QoS quantitatively in this paper. First, we introduce a system model based on a challenge/response authentication, which is widely used in various mobile environments. Then, a concept of security level is proposed to describe the protection of communications, which is classified with regard to the nature of security, i.e., information secrecy, data integrity, and resource availability. By taking traffic ...