Research and trials for reliable VoIP applications

The Internet has burgeoned into a worldwide information infrastructure during the past few years, bringing about significant changes in the telecommunications arena. One of the new applications that has thrived is Voice over IP (VoIP), also known as Internet or IP telephony. Since its inception, huge strides have been made in quality and usability and now VoIP enjoys widespread popularity as an alternative to traditional telephony in homes and enterprises. Despite promises of advanced services, VoIP is still mainly a PSTN replacement service and is measured against the public switched telephone network (PSTN) in terms of quality-of-service and reliability. Unfortunately, despite advances, it still comes up short, typically because of challenging network environments. VoIP always uses internet protocols to transport voice signals between caller and callee and to establish and manage calls (''signalling "). In some cases, the public Inter-net is used as a transport infrastructure. The combination of the use of widely deployed general-purpose protocols and the re-use of an existing infrastructure can offer significant functionality and cost advantages. For example, even for wired devices, phone numbers are no longer tied to a specific geographic location. Compared to the PSTN, it is fairly easy to add wideband audio, video, instant messag-ing and other media. Since end systems are built on general purpose programmable processors and have access to other Internet services such as the Web, telecommuni-cation providers and end users can more readily customize services to specific users and vertical markets. Sharing a single infrastructure can drastically reduce cost for wiring and switching bits, while providing more capacity for load spikes. Beyond those promises, however, the user experience and reliability of VoIP is still often inferior to that of classical circuit-switched PSTN services, particularly when the public Internet is part of the voice path. Varying degrees of packet loss, delay and jitter make for a challenging operating environment, in addition to problems related to network address translation (NAT), interoperability, and network stability that are beyond the scope of this special issue. In addition, IEEE 802.11 wireless networks were not designed with VoIP in mind, leading to additional problems for that class of access networks. Furthermore, the end-to-end security of VoIP is still an issue of concern. Motivated by the promise and challenges of VoIP, this special issue presents recent research activities addressing all aspects of VoIP communications. Of particular interest are studies that focus on the provision of VoIP …