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Gold Medal Software Volume 2 (Gold Medal) (1994).iso
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P131
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1994-02-13
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64 lines
The TriBBS Bulletin Board System 131
HIGH-SPEED MODEMS
-----------------
Because the price of high-speed modems has been dropping steadily over
the past year or so, many sysops have decided to take the plunge and
purchase either a V.32 or V.32bis modem. Unfortunately, most new
owners of high-speed modems quickly find that setting up a high-speed
modem can be rather confusing at first. This confusion occurs because
most sysops have never had any experience with locking a serial port.
Although locking a serial port is a very simple thing to do, modem
manuals generally assume that the modem owner knows all about the
subject.
The first step in understanding how a serial port is locked requires
you to understand a little communications-related terminology and some
of the reasons why it is beneficial to lock a serial port. First of
all, a modem is considered data communications equipment (DCE) and the
computer is considered data terminal equipment (DTE). When your modem
is communicating with another modem, there are essentially three links
in the communication path: your computer and modem are talking to each
other (DTE to DCE), the two modems are talking to each other (DCE to
DCE), and the other person's computer is talking with their modem (DTE
to DCE).
When a DCE to DCE connection is established, the modem will send a
CONNECT message to the computer. This CONNECT message tells the
computer what baud rate the two modems are talking to each other at.
Let's assume that your modem is a 9600 baud modem and that the caller
is calling with a 2400 baud modem. In a case like this, the modems
will establish a 2400 baud connection and your modem will send a
CONNECT 2400 baud message to your computer. If your serial port isn't
locked, the modem will switch the baud rate that it talks to the
computer with to 2400. In turn, the computer's communication program
(BBS software, terminal program, etc.) will set the computer's serial
port for 2400 baud. At this point, both the DTE to DCE and the DCE to
DCE baud rates will be set for 2400 baud.
Now lets assume that the serial port is locked at 19200 baud. When
your 9600 baud modem establishes the 2400 baud connection, it will
once again send a CONNECT 2400 baud message to your computer.
However, this time the modem will maintain the 19200 baud connection
it has with the computer instead of dropping down to 2400 baud.
Likewise, the computer's communication program will not lower the
computer's serial port to 2400 baud. So with a locked serial port,
the DTE to DCE baud rate will be 19200 and the DCE to DCE baud rate
will be 2400.
Why would you want to lock your serial port? Error correction and
data compression are the two best reasons. Error correcting
connections can transmit data about 20 percent faster than non- error
correcting connections. Also through data compression, modems can
send data up to four times faster than without data compression.