3Com OfficeConnect Getting Started Manual page 16

Mainframe computer keeps dropping your connection
Bad faxes or can't fax
Both devices exchange carrier signals, but fail to establish a communications link
You must turn off the Business Modem's result codes and character echo
(ATQ1E0). The modem at the mainframe also needs to be set to ATQ1E0.
Make sure the fax software is set to use Class 1 fax. Refer to your fax
software's manual.
If you use memory-resident programs (TSRs-Terminate and Stay
Resident programs) or disk-caching programs, they may be interfering.
Try disabling them before you run your communications software.
Make sure the Business Modem is in the correct mode, fax or data,
depending on whether the connection is to be made with a facsimile
device or a data device.
See Chapter 2, Modes of Operation, in the electronic 3Com
OfficeConnect 56K Business Modem Command Reference on the
Connections CD for information on switching between Fax and Data
modes.
Make sure the proper bit rate, word length, parity and number of Stop
bits have been selected.
Send ATI4 and check to see that your modem is at the correct Bn
setting to connect with either an HST modem (B1 setting) or "V."
modem (B0 setting).
Make sure that your Business Modem's connection rate setting, &Nn,
is correct for the call. If the connection rate is locked at a speed
(&N1-&N14) different from the calling modem's, the Business Modem
hangs up. The default setting of &N0, variable link operations, allows
the two modems to negotiate the highest possible connection rate.
If your modem is attempting to answer a V.32 call, you may need to
lengthen the extra V.32 answer tones. See under S28 in Appendix B
(Alphabetic Command Summary) in the electronic 3Com
OfficeConnect 56K Business Modem Command Reference on the
Connections CD.
Problems that Occur After Connecting 3-5