Firewalls

(RTC) between individuals, a capability that is becoming highly

useful as more and more individuals have broadband or a fixed

connection to the Internet.

Several forms of P2P communication over the Internet have

already been in use for a few years. However, it is just now, when a

general standard has been established, that these types of applica-

tions have become more available and more widely used. SIP is the

Internet standard for such applications and currently has a strongly

accelerating growth.

The SIP Center (www.sipcenter.com) is a portal for the commer-

cial development of the SIP. Serving both the SIP community and the

wider industry, the SIP Center offers comprehensive technical and

market resources, as well as an environment for the testing of SIP

implementations.

Note:

A powerful driving force for SIP is that Microsoft has announced

that all future RTC will be based on the SIP standard. Windows

Messenger, which can be downloaded at no charge, already has a SIP

mode that provides the user with telephony, voice, video, presence,

and instant messaging, and Microsoft recently launched Greenwich,

the RTC services for the Windows 2003 server. Greenwich includes

a SIP server for safe enterprise usage and a programming application

program interface (API), which resulted in numerous SIP applica-

tions. With the market impact of Microsoft, there are now tens of

millions of SIP users.

1

15.3 Internet protocol telephony

SIP is also used for ordinary telephony (voice with 3-kHz bandwidth

and common number dialing) over IP networks. For this application,

the SIP standard is taking over from the earlier H.323 standard,

which is a protocol from the standardization organization of the

telecom world, the International Telecommunications Union-

Telecommunications (ITU-T). H.323 has been used to build islands

of VoIP, but most often without interoperability on the IP level

URLs are subject to change without notice.

250 15.3 Internet protocol telephony