User manual

CHAPTER 4: GENERAL INFORMATION AND FEATURES
4.5 Synchronous VS. Asynchronous
The data formats of both connecting modems must be exactly the same in order to
exchange data with each other.
There are synchronous and asynchronous data formats. The common personal
computers and terminals are asynchronous. Whereas, the host computers and their
terminals are often synchronous.
For most multiplexes, the connecting modems should be synchronous. However, the
user should know the type of the data terminal equipment (DTE) to get proper
operation.
Except V.21, V.23, and Bell 103 which only can operate in asynchronous mode, other
protocols can run in either mode.
About the settings of this issue, you may find it at “Data Format” column of
“CONFIG DTE” menu. Note that if the asynchronous mode is selected, you need to
set “Data Bits”, “DTE Speed”, as well. On the other hand, if you operate the modem
with “AT” command, it will automatically determine these parameters.
4.6 Error Correction And Data Compression
The Network Series Modem supports “Error Correction” and “Data
Compression” while operating in asynchronous mode. In addition to 100% error free,
it also provides two to four times data compression rate to increase throughput.
MNP class 4 provides error corrections. MNP class 5 provides data compression for
up to two times. On the other hand, V.42 and V.42bis are the recommendations from
ITU-T V.42 to provide error correction and V.42bis provides data compression for up
to four times.
Due to the improved throughput, the modem it provides DTE speed up to 115200 bps
for between data terminal and modem.
During connecting, the modem automatically recognizes the protocol being used by
the remote modem and set the priority order as LAPM with EC→LAPM→MNP-5→
MNP-4→NORMAL.
Under these error correction and data compression operations, there should be some
kinds of flow control between modem and data terminal equipment (DTE) to avoid
data loss. the hardware solution to the modem is by controlling RTS and CTS signals.
The software solution is by utilizing X-on and X-off codes.
To find the setting information dealing with error correction and data compression,
you may look up the “PROTOCOL” menu. In addition, “CONFIG DTE” menu gives
you the guide to flow control setting.
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