An H.323 gatekeeper prototype: design, implementation, and performance analysis

In recent years, Internet telephony or voice-over IP is attracting an increasing amount of attention for the reason that it has the potential to significantly reduce the cost of long-distance voice communication. To provide the interoperability between different manufacturers and vendors, ITU-T is actively drawing up the standard for the Internet telephony as ITU-T Recommendation H.323. While H.323 is continuously revised, there are, however, still many important issues needed to be further discussed. In particular, the bandwidth management, address translation, and intelligent call signaling/routing, which are the major functions of an H.323 gatekeeper, have not yet been fully addressed. In view of this, we develop in this paper an H.323 gatekeeper prototype which fully complies with the H.323 recommendation, and explicitly illustrate the usefulness of this prototype by devising two improved call-routing methods to deal with the load-balancing problem among the gatekeepers. As a matter of fact, the existing call-routing method used in the current version of the H.323 is very primitive and will cause the loads of the gatekeepers unbalanced. Using the gatekeeper prototype devised, two improved call-routing methods are proposed based on Multiple-Registration with Multicasted Location Request (MRML) and Multiple-Registration with Hierarchical Database (MRHD). To evaluate the performance improvement by these two load-balancing methods, we design an event-driven simulator and conduct some experiments on it. We focus on two performance metrics, call-blocking rate and channel utilization , which are both sensitive to the load distribution. The experimental results show that the call-blocking ratio and channel utilization are optimized with the proposed load-balancing methods. It is also observed from our empirical results that the call-blocking ratio is more sensitive to the traffic load whereas the channel utilization is more sensitive to the duration of a call.