What is Packet Switching

The founding of the Bell Telephone System, the public switched telephone network (PSTN), has evolved into a highly successful global telecommunications system. It is designed specifically for voice communications, and provides a high quality of service and ease of use. It is supported by sophisticated operations systems that ensure extremely high dependability and availability. Over the past 100 years, it has been a showcase for communications engineering and led to groundbreaking new technologies (e.g., transistors, fiber optics). Yet it is remarkable that many public carriers see their future in Internet protocol (IP) networks, namely the Internet. Of course, the Internet has also been highly successful, coinciding with the proliferation of personal computers. It has become ubiquitous for data applications such as the World Wide Web, e-mail, and peer-to-peer file sharing. While it is not surprising that the Internet is the future for data services, even voice services are transitioning to voice over Internet protocol (VoIP). This phenomenon bears closer examination, as a prime example explaining the success of the Internet as a universal communications platform. This chapter gives a historical development of the Internet and an overview of technical and nontechnical reasons for the convergence of services.