  Voice over Internet Protocol (VoIP) technologies are integral to modern
telecommunications because of their advanced features, flexibility, and
economic benefits. Internet Service Providers initially promoted these
technologies by providing low cost local and international calling. At present,
there is also a great deal of interest in using IP-based technologies to
replace traditional small and large office telephone systems that use
traditional PBXs (Private Branch eXchange). Unfortunately, the large majority
of the emerging VoIP based office telephone systems have followed the
centralized design of traditional public and private telephone systems in which
all the intelligence in the system is at the core, with quite expensive
hardware and software components and appropriate redundancy for adequate levels
of reliability. In this paper, it is argued that a centralized model for an
IP-based telecommunications system fails to exploit the full capabilities of
Internet-inspired communications and that, very simple, inexpensive, elegant
and flexible solutions are possible by deliberately avoiding the centralized
approach. This paper describes the design, philosophy and implementation of a
prototype for a fully distributed IP-based Telecommunication System (IPTS) that
provides the essential feature set for office and home telecommunications,
including IP-based long-distance and local calling, and with the support for
video as well as data and text. The prototype system was implemented with an
Internet-inspired distributed design using open source software, with
appropriate customizations and configurations.
