Communications have been known not to be dependent on the location on the Internet. Application-level mobility based on SIP is a key component to seamless mobile communications, as discussed in Chapter 15, “SIP Application Level Mobility.” Emergency calling services by users in distress using the Internet (such as 911 in the United States or 112 in Europe) are far more powerful and cost less than the Public Switched Telephone Network (PSTN) based emergency services.
Internet-based emergency calling is indeed in the design stage in a number of countries. Chapter 16, “Emergency and Preemption Communication Services,” discusses Internet-based emergency services. The multimedia nature of Internet communications gives hearing- and speech-impaired people the opportunity to fully participate in rich communications for work and in personal life.
“Accessibility for the Disabled,” discusses access to communications for disabled people. The Rise of Peer-to-Peer Communications P2P traffic has risen in the Internet since around 2000 and became the dominant part of Internet traffic by 2004. Since 2004, Skype (which is based on P2P VoIP, IM, and presence) has also become by far the dominant VoIP provider worldwide. Since P2P SIP standards work is just emerging as of this writing, Skype can be considered a prestandard P2P Internet communication service.
The reasons for the emergence of overlay networks and P2P applications and their nature are discussed in Chapter 20, “Peer-to-Peer SIP,” and also in Chapter 6, “SIP Overview.” Though the present VoIP industry is built on client-server (CS) SIP, this may significantly change. To quote David Bryan from p2p.org: