Lucent Technologies Definity Enterprise Communication Server 8.2 Manuale Utente

Issue 1

April 2000

Features and technical reference 

1570

Trunks and Trunk Groups 

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Start-dial signal 

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 The distant office’s acknowledgment that it is ready to 

accept dialing from the originating office.

E&M supervision is a symmetric signaling scheme used on private network 
trunks. DC voltage levels are sent over E&M leads, which are separate from the 
transmission path. E & M signals indicate on-hook and off-hook states for each 
end of the connection path.

DIOD trunk groups support Continuous and Pulsed E&M Signaling that allows 
you to make and receive calls over Brazil pulsed or continuous E&M signaling 
trunks and Hungarian pulsed E&M signaling trunks. Refer to DEFINITY ECS 
Application Notes for Type Approval for more information.

Ground-start signaling is a supervisory signaling scheme used on public network 
trunks in which ground is applied on the tip (T) lead by the CO and on the ring (R) 
lead by the switch. For example, the calling switch on a call to a CO seizes the 
outgoing trunk by placing a ground on the trunk interface R lead. The CO 
recognizes the trunk seizure as a request for service and grounds the trunk T lead 
to indicate to the calling switch that the CO is ready to receive digits. Ground-start 
signaling is superior to loop-start signaling (described below) for the following 
reasons:

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The switch can make trunks busy to outgoing calls almost immediately, 
because the tip ground seizure by the distant switch minimizes the interval 
during which a two-way trunk can be seized from both ends (called glare). 

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Ground-start signaling allows answer supervision, a positive indication that 
a distant switch has disconnected from a call. Answer supervision has 2 
benefits:

— Callers who remain off-hook after completing a call won’t be 

connected to central office dial tone. For example, this prevents a 
restricted station from making an unauthorized call after placing an 
authorized call using the attendant.

— By holding the trunk busy until the central office disconnects, 

another switch cannot seize the trunk and be connected to the CO 
party of the previous call.