VoIP Solution Workbook- POTS (Plain Old Telephone Service)

Plain old telephone service, or POTS, is a term which describes the voice-grade
telephone service that remains the basic form of residential and small business
service connection to the telephone network in most parts of the world. The name
is a reflection of the telephone service still available after the advent of
more advanced forms of telephony such as ISDN, mobile phones and VoIP. It has
been available almost since the introduction of the public telephone system in
the late 19th century, in a form mostly unchanged to the normal user despite the
introduction of Touch-Tone dialing, electronic telephone exchanges and
fiber-optic communication into the public switched telephone network (PSTN).

The system was originally known as the Post Office Telephone Service or Post
Office Telephone System in many countries. The term was dropped as telephone
services were removed from the control of national post offices.

POTS services include:

bi-directional, or full duplex, voice path with limited frequency range of 300
to 3400 Hz: in other words, a signal to carry the sound of the human voice both
ways at once; call-progress tones, such as dial tone and ringing signal;
subscriber dialing; operator services, such as directory assistance, long
distance, and conference calling assistance; a standards compliant analog
telephone interface including BORSCHT functions In the United States, the pair
of wires from the central switch office to a subscriber's home was called the
subscriber loop. It was typically powered by 48V direct current (DC) and backed
up by a large bank of batteries (connected in series) in the central office,
resulting in continuation of service during most commercial power outages. The
subscriber loop would typically carry a "load" of about 300 Ohms, and did not
pose a threat of electrocution to human beings (although shorting the loop could
be felt as an unpleasant sensation).

Many calling features became available to POTS subscribers after computerization
of telephone exchanges during the 1970s and 1980s. The services include:

Voicemail Caller ID Call waiting Speed dialing Conference call (three-way
calling) Enhanced 911 Centrex among other services.

The communications circuits of the PSTN continue to be modernized by advances in
digital communications, however, other than improving sound quality, these
changes have been mainly transparent to the POTS customer. The function of the
POTS local loop presented to the customer for connection to telephone equipment
is practically unchanged and remains compatible even with telephones built in
the early 20th century.

Due to the wide availability of POTS, new forms of communications devices such
as modems and facsimile machines are designed to use the POTS service to
transmit digital information.

Reliability While POTS provides limited features, low bandwidth and no
mobile capabilities, it does provide greater reliability than other telephony
systems (mobile phone, VoIP, etc.). Many telephone service providers attempt to
achieve "dial-tone availability" more than 99.999% of the time the telephone
is taken off-hook. This is equivalent to having no dial-tone available less than
five minutes each year, and was an often-cited benchmark in marketing and
systems engineering comparisons, the so-called "five nines" reliability
standard.

Attributes and Credits-The information and facts supplied on this subject
derive from http://en.wikipedia.org/wiki/Main_Page

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