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A reasonably good introduction to the basics of VoIP and its operation is given at this site (1). Special consideration is given to the implementation of VoIP systems and standards; the material can be fairly technical in nature, but the majority should be useful even for people with no prior background in the subject. A much more in-depth overview can be found in this tutorial from the International Engineering Consortium (2). A number of possible applications for VoIP are outlined, and the major technological challenges that face system designers are briefly touched upon. Additional sections about fax over IP are also presented. A professor at Columbia University points out the need for special handling of emergency call services, such as 9-1-1 in the US, in VoIP systems (3). His research paper identifies several key difficulties in accommodating emergency numbers and recommends solutions to them. Furthermore, the advantages to having a VoIP-based emergency call service are discussed. VoIP systems can be used as backups to conventional public switched telephone networks (PSTN), as is proposed by a working group of the Internet2 consortium (4). The group's Voice Disaster Recovery Project is investigating a method of transferring voice communications from phone lines to data networks in the event of a failure in the PSTN, with little or no interruption. Although the work is just beginning, the group's homepage offers background information about the project, press releases, and a slide presentation from an April 2003 talk. The problem of having a mobile endpoint for a VoIP terminal, such as in a wireless local area network, is discussed in a paper from Dartmouth College (5). The implementation issues associated with a Mobile Voice over IP system are highlighted, including how to maintain a connection when the network address of one of the hosts changes. Information technology professionals and anyone working with VoIP systems should find the next two resources to be quite useful. The first is a collection of architectural specifications, network protocols, and technical papers related to virtually every aspect of VoIP (6). Detailed articles and standards information are regularly updated on the site. The second resource is the Voice over IP Calculator Web site (7), which actually consists of four free online tools that can be used to estimate bandwidth requirements and voice paths for a planned VoIP system. Each utility is very easy to use, but is mainly intended for experienced IT workers. Lastly, a September 5, 2003 news article (8) recognizes Coldwater, Michigan as being the first US city to offer VoIP services in addition to conventional telephone services. The move is seen as a way of spurring competition and allowing cities to essentially go into business against local telecommunications companies.
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