The Growing Use of the Public Switched Telephone Network for Non-Voice ApplicationsThe American Public Switched Telephone Network (PSTN) is quite possibly the largest distributed system in existence. Most telephone switching networks do the same thing as PSTN by following a simple procedure: they essentially connect point A to point B. Although this seems like a very simple thing to do, it is not always the easiest. simple. The US PSTN requires some of the most complex computer systems in existence. Each switch's software can contain several million lines of code, even if it doesn't have many features. The PSTN is the global network of interconnected voice-oriented public telephone networks. The PSTN is both commercial and public. It is also said to be the good old telephone service. This is the same as the telephone networks that appeared during the time of Alexander Graham Bell, who started the entire history of the telephone. Today, technology is almost entirely digital, with the exception of the telephone exchange which, for the user, has thousands of switches. The switches have lots of redundant hardware and plenty of self-checking and recovery software. For many decades, AT&T expected its switches not to fail for more than two hours in forty years. This represents a failure rate of 5.7 x 10^-6. When it comes to the Internet, PSTN actually helps much of the long distance Internet infrastructure. Because Internet service providers (ISPs) pay long-distance providers for access to their infrastructure and share circuits among all users, Internet users avoid having to pay usage fees to anyone other than their ISP. The PSTN is part of the fixed telecommunications network. of KPN Telecom for narrowband switched services. A general description of this type of network is provided. For most of the history of telephone networks, direct conversation between two people and voice telephone service was the only basic thing that PSTN did. The 300 to 3,400 Hz bandwidth makes it designed for this purpose. Even today, voice transmission remains the most common use of PSTN, but it is also used for several different things, called non-voice services. .