28
Recently, phone companies have begun to deliver a digital line (in the form of a T-1, equivalent to
48 voice lines) from their Central Office to the ISP. By upgrading ISP dial-up modems with a digital
connection to a T-1 line, one less analog to digital conversion is made between the ISP and their
Central office. This reduces the amount of error introduced into the transmission, and provides for
data rates up to 56,000 bps delivered to homes and offices from an ISP over standard copper twisted-
pair lines.
56 Kbps Asymmetric Data Rates
Your 56K modem uses asymmetric data rates; the send and receive speeds differ. While your modem
is capable of
receiving
at a rate of 56,000 bps, the send rate is 33,600 bps or lower.
56 Kbps Requirements
For you to achieve 56 Kbps performance from your modem, your ISP must have these items in
place:
•
a connection to
their
phone company using a digital link (i.e., a T-1 line)
•
a modem rack which uses K56 flex technology (as listed by Rockwell).
33,600
BPS
C
ONNECTIONS
Your modem supports 33,600 bps connections with modems from many different manufacturers.
However, it may be unrealistic to expect that you will always be able to achieve full 33,600 bps data
speeds every time you connect with another 33.6 Kbps modem. Line conditions, serial port speed
and other factors impact actual connection speeds.
Unlike earlier modems, 33,600 bps modems are designed to modify their actual transmission speeds
during a data connection; so a minor difference in the phone line can have a significant impact on
the connection. For example, during one attempt to make a connection, you might connect at only
24,000 bps while a later call on the same lines and to the same modem may result in a 33,600 bps
connection.
One reason for such variable results is that speeds of 33,600 bps are higher than normal analog
phone lines were designed to handle. Data communications of 33,600 bps are best achieved when
the phone lines between the two modems are of high quality and are free of limiting factors such as
line noise.
Another factor to keep in mind when you are attempting high speed communication is the modem
on the other end of your connection. While all 33.6 Kbps modems use the same core technology, not
all of them may be as capable as yours. If you are unable to achieve the top data speeds, it may be
that the modem to which you are connecting is adjusting the speed down because it is unable to
communicate at top speed.
The slowdown may also be because the computer at the other end of the connection is not capable
of the highest speeds.
