Nortel DMS-100 Series Maintenance Manual page 135

Note: The S9CD271A SPOTS channel unit, which is not recommended
for use in a Mode III RCS, can be used for this purpose. Even-numbered
circuits can be assigned in Mode III.
The SPOTS channel unit does not provide for tip-ring reversal. Tip-ring
reversal is a signal for many switches to indicate a toll call to the
originating party. When this event occurs, the system can restrict the
SPOTS channel unit to nontoll calls. This restriction occurs when the
system connects the SPOTS channel unit to a PBX or other piece of
equipment that requires tip-ring reversal.
The system tests the SPOTS channel unit the same as a single-party line.
The system supports the following tests on the SPOTS channel:
off-hook detection
on-hook detection
echo return loss
single party ringing
carrier channel loss
idle channel noise
DMS-100 Family SMS Maintenance Manual XPM10 and up
SMS signaling 3-19