NAT/Firewall traversal cost model for publish-subscribe systems

We consider large scale Publish/Subscribe systems deployed across multiple organizations. However, such cross organizational deployment is often hindered by firewalls and Network Address Translators (NATs). Several workarounds have been proposed to allow firewall and NAT traversal, e.g. VPN, connection reversal, relay routers. However, each traversal mechanism in turn leads to trade-offs with respect to implementation complexity, infrastructure overhead, latency, etc. We focus on the latency aspect in this work. We propose a cost-performance model that allows quantitative evaluation of the performance latency induced by the different firewall traversal mechanisms. The utility of the model is that for a given network configuration, it is able to provide a (close) approximation of the performance latencies based on simulation results, without actually having to deploy them in practice. This also allows selecting the best traversal mechanism for a given configuration. Finally, experimental results are given to show the validity of the proposed model.