What is the public switched telephone network?

Answer 1

PSTN (public switched telephone network) is the world's collection of interconnected voice-oriented public telephone networks, both commercial and government-owned. It's also referred to as the Plain Old Telephone Service (POTS). It's the aggregation of circuit-switching telephone networks that has evolved from the days of Alexander Graham Bell ("Doctor Watson, come here!"). Today, it is almost entirely digital in technology except for the final link from the central (local) telephone office to the user.

In relation to the Internet, the PSTN actually furnishes much of the Internet's long-distance infrastructure.

A domestic telecommunications network usually accessed by telephones, key telephone systems, private branch exchange trunks, and data arrangements.

Ø In North America, you have access to the Public Switched Telephone System (PSTN). The term PSTN used to refer to the public communication system that provides local, extended local and long distance telephone service to the majority of the United States and North America. This system is made available to the public through a group of common communications carriers such as American and Canadian phone companies who have agreed to exchange calls and connections on behalf of their subscribers as mandated by international law and the laws of the country in which they do business and and provide telephone service. Anyone who subscribes to this public service may make calls to anyone else who has purchased access to the phone system through any other carrier.

Routing calls requires multiple switching offices. The phone number itself is a coded map for routing the call. In the United States, for example, we have 10-digit phone numbers.

• The first three digits are the area code or national destination code (NDC), which helps route the call to the right regional switching station.
• The next three digits are the exchange, which represents the smallest amount of circuits that can be bundled on the same switch. In other words, when you make a call to another user in your same exchange -- maybe a neighbor around the corner -- the call doesn't have to be routed onto another switch.
• The last four digits of the phone number represent the subscriber number, which is tied to your specific address and phone lines.

Within a company or larger organization, each employee or department might have its own extension. Extensions from the main phone number are routed through something called a private branch exchange (PBX) that operates on the premises.

To make an international call requires further instructions. The call needs to be routed through your long-distance phone carrier to Another Country's long-distance phone carrier. To signal such a switch, you have to dial two separate numbers, your country's exit code (or international access code) and the corresponding country code of the place you're calling.

Almost all exit codes are either 00 or 011, although there are a few exceptions like Cuba (119) and Nigeria (009). Country codes are one- to three-digit prefixes that are assigned to specific countries or groups of countries. For example, the country code for the United States is 1, but the United States shares that country code with Canada and several smaller island nations like Jamaica, Puerto Rico and Guam. The country code for Mexico is 52 and Saudi Arabia is 966. Here's a full list of exit and country codes.