A comparative study of the SIP and IAX VoIP protocols

Recently, there has been a strong focus on the development of scalable voice over IP (VoIP) protocols, which are suitable for wide scale deployment. SIP (session initiation protocol) is one such protocol which has been the subject of extensive research over the past few years. More recently, IAX (interasterisk exchange protocol) has emerged as a new VoIP protocol which is steadily gaining credence among the open source community. Among the benefits claimed by the proponents of IAX are its simplicity, NAT-friendliness, efficiency and robustness. This paper makes three key contributions to VoIP research. Firstly, we undertake a comparative evaluation and analysis of the SIP and IAX protocols. Secondly, we report on the viability of utilizing the asterisk PBX as a foundation for conducting research performance studies for VoIP. Finally, we report on live experimental studies of SIP and IAX voice traffic in the Ottawa Metropolitan area. We experimentally studied the performance of voice calls initiated using SIP and IAX for a variety of delay and loss characteristics. In addition, we examined the performance of both protocols in the presence of packet reordering. Our preliminary observations demonstrate that the IAX protocol compares favourably in relation to SIP. More detailed studies are required to evaluate the performance of IAX-based voice traffic in large-scale deployment.