Figure 2.2 Call routing performed by a SIP proxy serverOverview of Services Provided by SIP Servers
Multimedia conferencing on the Internet was well developed by the research
and academic community by 1997. This has been reflected in the explosion of
commercial ventures for Internet multimedia during the past decade. Work
started at the same time to extend the Internet multimedia architecture for use
in telephony. Because of the enormous complexity and richness of services on
the PSTN, this work has taken much longer to develop, and only at the end of
2000 had it reached a critical mass where true reengineering of the telephone
system for the Internet was well understood.
In the history of science and technology, many new technologies have found
applications that were not envisaged by their inventors. With this limitation in
mind, the following sections will provide an overview of services that are sup-
ported by SIP servers, such as those used by public VoIP service providers and
in enterprise PBX networks.
The prevalent business model of VoIP service providers in early 2006, however,
is to not support any features that require going outside the walled garden. The
assumption of practically all VoIP service providers is that all services are pro-
vided in-house. This may change, however, as Internet-wide VoIP will mature.
Recent work has shown that all or most services performed by SIP proxy
servers in the network can also be performed by server-less P2P SIP.CPL
SIP Java servlets
SIP CGI
Special ServersUpload
CPL Scripts.Download
Servlets.Locally
Create CPL/XML
With GUI.SIP Device SIP ServerService LogicSIP Server18 Chapter 2