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Feature Reference
Trunks and trunk groups
1744 Administrator’s Guide for Avaya Communication Manager
November 2003
Ear & Mouth (E&M) supervision on digital trunks
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.
Ground-start (GS) supervision
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 server running Communication
Manager. For example, the calling server or 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 serverr/switch that the CO is ready to receive digits.
Ground-start signaling is superior to loop-start signaling (described below) for the following reasons:
•
Communication Manager can make trunks busy to outgoing calls almost immediately, because
the tip ground seizure by the distant server/switch minimizes the interval during which a two-way
trunk can be seized from both ends (called glare).
•
Ground-start signaling allows answer supervision, a positive indication that a distant media server
or 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 server or switch
cannot seize the trunk and be connected to the CO party of the previous call.
•
Loop-start (LS) supervision
—
A supervisory signaling scheme used between a telephone
and a media server or 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.
•
Reverse Battery (RB) supervision
—
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).
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) Communication Manager sends out or expects to receive. Different
transmissions of alerting are:
•
Automatic
—
The originating media server or switch sends no digits or start dial signal and
expects the terminating server or switch to complete the call. The call usually is completed by the
attendant or other service such as Centralized Attendant Service (CAS).
•
Immediate start
—
An originating server/switch sends digits immediately without waiting for
a start dial signal from a terminating server/switch.