Nortel DMS-100 Series Maintenance Manual page 134

3-18 SMS signaling
Integrated local specials The special plain ordinary telephone service
(SPOTS) channel unit (S9CD271A) supports POTS and special services like
the following:
The SPOTS channel unit is configured in loop or ground start mode. When
SPOTS channel units are configured in loop start, the units do not support
PBX. The SPOTS channel units cannot support PBX lines because these
lines require ground-start signaling and ground-start mode.
Ground-start lines are different from loop-start lines. The system handles
loop-start (tip and ring) in a different way to signal an off-hook. The system
acknowledges ground-start off-hooks but not loop start off-hooks.
The SPOTS channel unit has the following characteristics:
Refer to manufacturer documentation for more information.
The following limits associate with the SPOTS channel unit as used in the
SMS-RCS subsystem:
297-8231-550 Standard 09.01 August 1998
INWATS
OUTWATS
TWX
PBX
two voice-frequency, two-wire channels associated with each channel
unit
accessible for mechanized loop testing
there is no gain or frequency setting
required special service unit (SSU) to be configured in the associated
RCS
single-party 20 Hz ringing (–R ringing)
The system assigns a channel for both loop- and ground-start
configurations. A minimum of one DS-0 channel must be available for
nondedicated channel units, when the units are present on the RCS.
Note: Mode I does not have this limit, since four DS-1 links connect an
RCS to an SMS. A DS-0 channel is present for every circuit.
The use of a SPOTS card in Mode III is not recommended because a
Mode III RCS multiplexes 48 circuits on to two DS-1 links. Channel
units on a Mode III RCS must have a single circuit. The SPOTS channel
unit has two circuits, loop and ground. The system cannot disable the
circuit that is not in use.