that can, for example, transcode speech to text and text to speech, or insert
video for using a sign language. SIP-based communications for the disabled
are described in Chapter 17, “Accessibility for the Disabled.”SIP Orphans
Not all SIP-related work has as yet found its way into Internet standards, but
some of it is quite interesting.
SIP has been considered for other applications as well, besides VoIP, IM, and
multimedia. Significant work has been done, for example, to use SIP for the
control of home appliances [31]. P2P SIP has also been discussed for commu-
nication between home entertainment devices [32].Commercial SIP Products
At the time of writing the first edition of this book, published in 2001, we still
tracked the vendors for SIP products and service providers using SIP. This is
no longer possible, since practically everyone in the IT communications indus-
try, Internet products, and telecom services, wired and wireless are now using
SIP. It would be easier to count the exceptions, services that do not use
SIP, though there are a few significant ones, like Skype and Google Talk in- Even such closed services use SIP to connect to the rest of the world. A
well-ordered list of SIP products can be found on the pulver.comweb site
http://www.pulver.com/products/sip. The SIP products and services can be
classified in many ways from a market segment or from a technical perspec-
tive. Following are categories on the pulver.comweb site:
■■ SIP-aware firewalls and NATs
■■ SIP-PSTN and SIP-PBX gateways
■■ SIP servers
■■ SIP services
■■ SIP software components
■■ SIP software tools
■■ SIP user agents for the PC/laptop and for PDAs and mobile phones
Figure 2.6 shows two examples of popular desktop SIP phones.32 Chapter 2