VoIP: A comprehensive survey on a promising technology

The Internet has burgeoned into a worldwide information superhighway during the past few years, giving rise to a host of new applications and services. Among them, Voice over IP (VoIP) is the most prominent one. Beginning more as a frolic among computer enthusiasts, VoIP has set off a feeding frenzy in both the industrial and scientific communities and has the potential to radically change telephone communications. In this article, we survey all these aspects that have the greatest impact on the quality of voice communications over IP networks. The survey begins with the merits and demerits of VoIP, followed by the Quality of Service (QoS) requirements that voice imposes and a description of test methods for the assessment of speech quality. We then proceed with a delineation of the issues related to the conversion of analog voice to packets, namely we spell out the details of the most well-known voice codecs, while light is also thrown on voice activity detection and voice packetization. Header compression schemes receive intense scrutiny as well. We also provide an overview of the signaling protocols that are tailored to the needs of VoIP, and we continue with the comparison of the call admission schemes that are geared towards the QoS constraints of VoIP. The pivotal issue of security is then discussed, pointing out potential threats as well as approaches for tackling them. Finally, the survey concludes with a discussion on the feasibility of providing VoIP over challenging satellite links.