Section 10: POTS Operation and Usage Tips
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T E C H N O L O G Y
10.5.
Private Branch Exchanges (PBX), Private Automatic
Branch Exchanges (PABX), Business Systems
Avoid connecting a
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codec to a PBX, PABX, Key station, business system
or any other local switchboard. Easily said, the tricky bit is working out if you are
on one of these systems.
As a general guide, these devices have two characteristics:
a) Requires the dialing of an additional digit to access the PSTN
9
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b) Have more buttons and features than your average space shuttle.
WARNING:
Many of these systems are digital and have non standard
telephone line operating voltages. If you plug a digital PABX/PBX line into a
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codec, permanent damage may result from the high voltage pulses these
systems generate. Even if the PBX is not digital, the performance of the codec is
unlikely to be as good as a normal POTS/PSTN line.
If you have no option than using a PBX/PABX, search for a fax machine.
Thankfully, the overwhelming majority of fax machines are designed for analogue
POTS line operation and are normally on an extension optimized for fax
machines and data transmission. Substitute a normal phone for the fax machine
and verify correct operation. Use a normal phone, not a house supplied phone
as the house phone may have characteristics to match the existing PBX/PABX,
not a POTS line. After confirming correct phone operation unplug the phone
and attach the phone line to the codec.
10.6.
Line Checks
10.6.1.
Length of the line from your site to the Central Office or Local
Exchange
It is desirable to have a local loop (the line from your location to the local CO
or Exchange) as short as possible. Optimum performance can be expected
for lines up to about 2 miles (3 kilometers) in length. Lengths in excess of this
can be expected to perform at lower bit rates and line quality depending on
the age, condition and type of cabling. E.g. plastic insulation, paper
insulation, water or moisture entering the cable, age and state of repair of
joins.
10.6.2.
Presence of stub or party lines on your local loop
In some countries, it was the practice to have more than one phone service
attached to one line - sometimes called a Party Line. In this situation, as
more lines are installed, services are separated but the redundant cabling may
remain connected across the line. This scenario will cause problems with the
operation of your
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codec.
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PSTN Public Switched Telephone Network
