Guest Editorial

Internet telephony, by some measures, is now 15 years old. In the last 15 years, it has emerged from academic and commercial laboratories to become the mainstream method of communications today. The success of Internet telephony applications has demonstrated the feasibility of IP communications to support millions of concurrent users. What started initially as a technology for toll-bypass in the switched telephone network has now grown to subsume the switched telephone network. However, creating scalable innovative services for Internet telephony in a rapid manner is still a work in progress. The web service creation model served as an initial model of creating services in Internet telephony and, to a great extent, still continues in the same role. As web mashups proliferated, voice mashups gained currency; as RSS feeds lead to innovative web services, the voice market capitalized with voice-enabled RSS feeds. Added to this mix are more recent technological advances such as virtualization, virtual worlds, IMS and mobile technologies, and capable personal digital assistants -- all enabling a variety of new communication protocols, services and architectures. It is our great pleasure to bring you this special issue on IP Communication Services. The special issue contains five papers that explore innovative and significant research on recent advances in architecture, system, protocol, and modeling, as well as emerging applications and standards related to IP Communication Services. The first two papers are invited survey papers. The Session Initiation Protocol (SIP): An Evolutionary Study by Baset et al. reviews the history and key contributions of the Session Initiation Protocol (SIP), a fundamental protocol for IP communication services. As SIP has matured, operational issues have taken to the forefront. The paper explores the genesis of SIP, touches upon the many ways in which the protocol is deployed in today's networks, looks at operational issues and more importantly, takes a critical look at where SIP succeeded and where it did not. The second invited paper, Service Program Mobility: A New Paradigm for Mobile Operators’ Service Delivery by Lundqvist et al. describes an approach for service mobility for roaming users. As the society becomes more mobile and personal device