User`s manual

The AUXIN and AUXOUT signals on the RJ-11 connector must be
determined as well. AUXIN may be selected to be either CTS or DSR.
AUXOUT may be selected to be either RTS or DTR. The decision of which
signals to use is made separately for each channel.
Figure 13 --- Auxiliary signal configuration jumpers.
12 Quatech QS-100M/ES-100M User's Manual