Allied Data Technologies TRON SECURE 33.6, Manual

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This is how Xon/Xoff flowcontrol functions:
As soon as the modem-buffer reaches a certain limit, the modem sends the Xoff character (in
ASCII: ^S) through the serial port to the computer. It reacts to this by sending no more bytes to the
computer. When the buffer is almost empty, the Xon character (in ASCII: ^Q) is sent to the
computer.
N.B. The flow control of the communication software has to be active!
Some transmission protocols, such as Xmodem and Zmodem, do not combine properly
with the Xon/Xoff flow control. Therefore RTS/CTS is the most commonly used type of
flowcontrol.
6.3 Error correction and data compression
When two modems communicate, invalid characters can be received as a result of disturbance
on the telephone line.
In order to prevent the reception of wrong information, protocols have been developed which
check and, if necessary, correct the information. MNP (Microcom Networking Protocol) and V42
LAPM are protocols which recognize and correct an error. To compensate the speed loss caused
by this, there is a possibility to compress the data to be sent. MNP5 and V42bis have a
compression technique with which an effective bit speed can be reached which is greater than
with a normal connection. This means that with a V34 28,800 connection, a speed higher than
28,800 bps can be attained. MNP5 can compress by a factor 2, so the effective speed can reach
a maximum of 57,600 bps.
V42bis can compress by a factor 4, at which a line speed of 115,200 bps can be reached.
Note: The speeds mentioned are theoretically reachable speeds. The compression factor mainly
depends on the content of the file which is sent. Therefore, a text file can be easily compressed,
where data-compression is not very useful on already compressed ZIP, ARJ, or ARC files.
E rro r- c o rrection and data-compression will work with V22, V22bis, V32, V32bis and V34
connections only. It is obvious that the speed of the serial port must be as high as possible,
preferably 115,200 bps.
TRON SECURE 33.6
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