Reducing the Recovery Time of IP-Phones in an H.323 Based VoIP System

Abstract

In large deployments of H.323 based Voice-over-IP (VoIP) systems, achieving the desired availability is a major challenge. A major factor in determining the availability is the resilience of the recovery mechanisms in the H.323 protocol suite against server and network failures. In this paper, we focus on the “registration” aspect of the H.225 protocol in H.323 suite. Specifically, we tackle the registration-flood problem which occurs after a server or network failure, when more IP Phones attempt to register with the VoIP server than the server can handle. The most significant ramification of overload is longer registration times resulting in lower overall availability of the VoIP system. Existing solutions to mitigate registration-floods are either server centric or network centric. In this paper, we propose a complementary end-point based technique using random back-off. Discrete event simulation based evaluation shows that the proposed technique can yield significant reduction in the recovery time thereby increasing service availability. We also compare the performance of existing solutions with the proposed technique, particularly the relative effect of network delay and loss on the performance of the techniques.