How to choose your long distance service

At a very basic level, the telephonic system in state can be split in two major categories, from a technological point of view: Time Division Multiplex (TDM) and Voice Over Internet Protocol (VoIP).

Time division multiplex is a method of inserting multiple streams of voice through a single signal, achieved by splitting the signal in many segments, each having a very short duration. Each individual voice channel is reassembled at the receiving end, based on the timing.

The equipment that combines signals at the source end (transmitter) of a communication link is known as a multiplexer. It accepts the input from each individual user , breaks each signal into segments, and assigns the segments to the composite signal in a rotating, repeating sequence. The composite signal thus contains data from multiple senders.At the other end is the demultiplexer, who is reversing the steps listed before.

TDM is used as the backbone for the Public Switched Telephone Network (PSTN). PSTN is a 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).

VoIP (voice over IP - that is, voice delivered using the Internet Protocol) is a term used in telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol (IP). This means sending voice information in digital form in packets rather than in the traditional circuit - committed protocols of the public switched telephone network (PSTN). A major advantage of VoIP and Internet telephony is that it avoids the tolls charged by ordinary telephone service.

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