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PREFACE:
Telephony refers to the telephone system and industry as a whole. In
these pages, the focus will be on the telephone service provider, a.k.a. Local Exchange
Carrier (LEC) and the connectivity they provide to the Internet.
Your LEC provides you and your local ISP with connectivity to the Plain
Old Telephone System (POTS). This refers to the standard old analog
telephone service that includes the copper wires and equipment inside of your
house and the copper wires and equipment between your house and the Central
Office (CO) called the POTS Plant, and the equipment inside of the CO,
specifically the Switch.
Your LEC's equipment determines the maximum rate at which your modem can
connect to your ISP. POTS can only guarantee 9600 bps. Ask
any telephone provider why your modem connections to your ISP are so slow and
they will quickly tell you that all they guarantee is 9600 BAUD. This
is due to two primary reasons. The first reason is the electronics in the
POTS Plant. The second reason is the performance envelope of today's
modems.
POTS PLANT ELECTRONICS:
The physical copper wires in the POTS Plant connect to the Switch.
The Switch used to be a mechanical or electro-mechanical device. The
purpose of the 'Switch' was to switch the wires coming from your house to other
wires at the CO whenever you made a telephone call. Hence it's name
'Switch'. These old devices are very rare today, if there are any still in
service at all. Almost all Switches found today are computer controlled
digital electronic devices. And these have been around for about 20
years. It is interesting to note that Integrated Services Digital Network
(ISDN) has been around since that time.
As you can see, the problem is the digital electronics in these switches
were developed before the Internet and fast modems. Switch electronics
were developed at a time when 9600 BAUD was king. The recent Internet
expansion has wildly outpaced the Telephony industry.
Although the telephone switch is a digital electronic device, it has the
job of converting it's digital signals into analog signals for compatibility
with POTS. Your telephone and fax machine use very old analog
technology. In order to provide compatibility with the zillions of
telephones and fax machines out there in the world today, the telephone Switch
has to make the conversion from digital to analog for information flowing to you
and from analog to digital for information flowing from you. This
technology has a physical distance limitation. The electrical signals can
only travel so far before they become unusable.
If you live more than about 12000 feet (2 miles) from the CO Switch, you
are most likely connected through a Remote Terminal (RT). The job of the
RT is to extend the Switch's physical distance. You can think of it as an
amplifier, but depending on the type, it can be far more. The older RT's
were basically amplifiers or concentrators that could only gaurantee 9600
BAUD. Today's RT's actually extend the basic digital functionality of the
newer Switches.
New electronic Switches and RT's that provide for the newer connectivity
technologies such as 56K modems, xDSL, and ATM have just started to roll off the
production lines this year. However, a typical telephone Switch and
associated RT's costs millions of dollars to replace/upgrade. Therefore,
these new electronic Switches and RT's are just entering service and are not
very wide spread. Furthermore, rural area telephony providers are less
likely to afford this new technology due to the limited Subscriber Base and low
Subscriber Density.
The Subscriber Base is the number of total subscribers, where I live,
that's about 5,000. The Subscriber Density is the number of subscribers
per distance, where I live, that's about 2 per mile. In a city, the
Subscriber Base could be 500,000 and the Subscriber Density could be 200 per
mile. Obviously, the more total monies a telephone provider has, the more
money it has to upgrade.
MODEM PERFORMANCE ENVELOPE:
Today's modems are really pushing the theoretical limits of POTS
technology and legal limits. Theoretical limits are always higher than the
real world practical limits. For instance, it may be theoretically
possible to travel to a star 1,000 light years away. But at almost the
speed of light, it would take you 1,000 years to get there. The 56K
modem has similar a similar quandary.
The Federal Communications Commission (FCC) limits the electrical signal
strength in the POTS. In order to achieve 56K, these modems would have to
violate those limits. Therefore, NO 56K modem can connect at
56K. If it does, it is by definition violating the law. And you and
your telephone provider can be prosecuted. Therefore, the practical limit
for 56K modems can only be as high as what the FCC allows, which is actually
53,333. The telephone Switch has limits physically built into it to
prevent the signal strength from going over the FCC limit. In other words,
the telephone Switch is DESIGNED to prevent 56K.
Even with newer Switches and RT's, fast analog modems assume almost
perfect conditions. This means that the copper wire between you and your
LEC CO are perfect. It assumes there are no bad connections, noise, water,
etc. That just isn't possible. It rains, snows, blows, hails,
sleets, freezes, heats and even worse. Lightning and Electro-Magnetic
Interference (EMI) is a big problem for any electrical/electronic device.
Think of the millions of miles of copper wire hanging out there on those poles
or buried in the ground exposed to the elemental forces of nature and
machine. It is an awesome problem when you think about. I'm really
amazed that it works as well as it does.
Don't be discouraged though. The telephony industry is moving to
meet these challenges. It may take some time though, the economics will
dictate the speed. If you suspect that you have line problems, consult your
telephone company. They are constantly fixing and maintaining the
Plant. They will check out your lines if you ask them to. Each and
everyday, telephony technicians find and repair loose or corroded connections,
broken shields, etc. It is a normal and natural procedure.
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