The Public Switched Telephone Network (PSTN) is a collection of all the world’s phone networks run by different operators. It provides the infrastructure and services for public phone calls. The network consists of telephone lines, fiber-optic cables, microwave links, cellular networks, satellites, and undersea cables connected through the switching centers. These centers provide the avenue for people to be able to call each other. These networks are moving towards using the Internet Protocol to carry their traffic.[1] The PSTN follows international standards set by the ITU-T. These rules originated with the local phone systems, principally from the Bell System in the US and networks in Europe. The E.164 standard provides a single global address space in the form of telephone numbers.[2]
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