■■ Security-sensitive organization—Security conscious small businesses or
organizations of various types may not feel comfortable using the
hosted “Centrex” type of communications that are marketed by tele-
phone companies or carriers. P2P removes the incentive to reduce cost
that is invoked for hosted services and allows self-contained, locally
resident secure communications.
■■ Limited or interrupted Internet connectivity—Communities can be isolated
from the Internet (such as on the battlefield or during natural or man-
made disasters). P2P communications will still function, as long as there
is a local, most-basic IP network available. Meshed wireless networks
can provide the IP infrastructure.
■■ Ad hoc groups—Groups of people that assemble for meetings or events
can set up an instant communication network. Here again, meshed
wireless networks can provide the IP infrastructure.
■■ Serverless PBX—Serverless IP PBXs were the first commercial applica-
tion of enterprise P2P communications. We expect serverless multime-
dia communications for the enterprise to be a successor to the serverless
IP PBX that can support only voice. Enterprise systems may require a
login server, however, just like public P2P service providers.
■■ P2P for self-organizing SIP proxies—Even CS SIP-based communication
systems can reduce their operational costs by deploying a self-organizing
P2P cloud of SIP registrars, SIP proxies, and component services, as
described in Chapter 19. Self-organizing SIP proxies can also use DNS as
described for the commercial SIP Thor product [19]. DNS can be used
for self-organizing systems of small scale. A SIP server cloud is a small
system, though it can serve millions of users.Disruption of the VoIP Infrastructure Model
The original concept of the Internet regarding the end-to-end principle and
best-effort quality of service has found a triumphant vindication in the market
with Skype, by far the dominant VoIP, presence, IM, and video service world-
wide. As mentioned, Skype can be rightly considered as a prestandard imple-
mentation of P2P Internet communications. An analysis of Skype can be found
in [20]. The success of P2P Internet communications can be explained mainly
by a number of factors [21]:
■■ Minimal or no VoIP infrastructure capital cost for such items as:
■■ SIP registrar and proxy servers
■■ Session border controllersPeer-to-Peer SIP 349