DEFINITY ECS Release 8.2
Administrator’s Guide
555-233-506 Issue 1
April 2000
Features and technical reference
1571Trunks and Trunk Groups
20
■Loop-start (LS) supervision — A supervisory signaling scheme used
between a telephone and a switch in which the telephone or far-end office
completes the current path formed by the trunk wires. The circuit provides
one signaling state when it is open and another when it is closed. A third
signaling state is achieved by changing the direction or magnitude of
current in the loop. The preferred method of loop-start signaling is reverse
battery signaling. Disconnect times when using loop-start signaling can
result in delays of up to 10–20 seconds. Glare, as described in ground-start,
is possible.
Loop-start signaling does not provide answer supervision. This lack can
open a potential for toll fraud in some situ ations, especially when incoming
calls are forwarded off-net. Loop-start is used with analog DIOD trunks,
but in general try to use loop start only with one-way trunks.
■Reverse Battery (RB) supervision — A supervisory technique on
one-way trunks that uses open and closure signals from the o ri ginating end
and reversals of battery and ground from the terminating end (normally
used on direct inward dialing trunks).
Start-dial signals
Network trunks operate as automatic, immediate start, dial tone, wink start, or
delay dial according to the type of start-dial signal (alerting) the switch sends out
or expects to receive. The different transmissions of alerting are:
■Automatic — The originating switch sends no digits or start dial signal
and expects the terminating switch to complet e the call. The call usually is
completed by the attendant or other service such as Centralized Attendant
Service (CAS).
■Immediate start — The originating switch sends digits immediately
without waiting for a start dial signal from the terminating switch.
■Dial tone — The terminating switch sends precise dial tone to the
originating switch. This indicates that the terminating switch is ready to
receive digits.
■Wink start — The terminating switch sends a wink st ar t (momentary
off-hook) signal to the originating switch. This indicates that the
terminating switch is ready to receive digits.
■Delay dial — The terminating switch sends a delay dial signal (an
off-hook signal followed by an on-hook signal) to the originating switch.
This indicates that the terminating switch is ready to receive digits.