Balancing Request Denial Probability and Latency in an Agent-Based VPN Architecture

Agent-based virtual private networks architecture (ABVA) refers to the environment where a third-party provider runs and administers remote access virtual private network (VPN) service for organizations that do not want to maintain their own in-house VPN servers. In this paper, we consider the problem of optimally connecting users of an organization to VPN server locations in an ABVA environment so that request denial probability and latency are balanced. A user request needs a certain bandwidth between the user and the VPN server. The VPN server may deny requests when the bandwidth is insufficient (capacity limitation). At the same time, the latency perceived by a user from its current location to a VPN server is an important consideration. We present a number of schemes regarding how VPN servers are to be selected and the number of servers to be tried so that request denial probability is minimized without unduly affecting latency. These schemes are studied on a number of different topologies. For our study, we consider Poisson and non-Poisson arrival of requests under both finite and infinite population models to understand the impact on the entire system. We found that the arrival processes have a significant and consistent impact on the request denial probability and the impact on the latency is dependent on the traffic load in the infinite model. In the finite model, arrival processes have an inconsistent impact to the request denial probability. As to the latency in the finite model, arrivals that have a squared co-efficient of variation less than one is consistently largest, followed by the Poisson case, then the case that the squared co-efficient of variation is more than one. Finally, a strength of this work is the comparison of infinite and finite models; we found that a mismatch between the infinite and the finite model is dependent both on the number of users in the system and the load.