Analytical Modeling and Performance Study of TGREP System

Interworking of Voice over IP (VoIP) network with traditional Public Switched Telephone Networks (PSTN) is essential for wide adoption of VoIP services. Telephony gateways act as interface between PSTN and IP telephony networks. These gateways use Telephony Gateway REgistration Protocol (TGREP) to advertise their resource information to Location Servers which are responsible for routing calls to appropriate gateway. The periodic interval, known as update interval (UI), at which gateways advertise their resources play an important role in deciding the performance of TGREP system in terms of call blocking probability. In this paper, we provide an analytical method to model TGREP system. To the best of our knowledge, this is the first study which provides accurate modeling of TGREP system. We validate our model by comparing its characteristics with that of a discrete event simulator developed by us. Using the model, we then analyze the performance of TGREP system as various operating parameters, like update interval, load, call arrival rate and average call length change. This study gives very useful insight into the system. For example, our study shows that a TGREP system should never run above relative load of 1.0 in order to keep the blocking probability below 0.1. Our study also shows that when system is running with light load, update interval can be arbitrarily large. Based on our study, we have provided a reference table which, will be useful for TGREP system administrators in setting update interval based on the system configuration and load.