Lucent Technologies Definity Enterprise Communication Server 8.2 User Manual

Issue 1

April 2000

Features and technical reference 

1571

Trunks and Trunk Groups 

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 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 situations, 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.

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 A supervisory technique on 

one-way trunks that uses open and closure signals from the originating end 
and reversals of battery and ground from the terminating end (normally 
used on direct inward dialing trunks).

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:

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 The originating switch sends no digits or start dial signal 

and expects the terminating switch to complete the call. The call usually is 
completed by the attendant or other service such as Centralized Attendant 
Service (CAS).

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 The originating switch sends digits immediately 

without waiting for a start dial signal from the terminating switch.

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 The terminating switch sends precise dial tone to the 

originating switch. This indicates that the terminating switch is ready to 
receive digits.

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 The terminating switch sends a wink start (momentary 

off-hook) signal to the originating switch. This indicates that the 
terminating switch is ready to receive digits.

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 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.