3Com VCX v7111 User Manual page 258

Call Flow for Two-Stage Dialing
Figure 99
Two-stage dialing implements the Dialing Time feature. Dialing Time allows you to define the
time that each digit can be separately dialed. By default, the overall dialing time per digit is
200 msec. The longer the telephone number, the greater the dialing time will be.
The relevant parameters for configuring Dialing Time include the following:
DTMFDigitLength (100 msec): time for generating DTMF tones to the PSTN (PBX) side
DTMFInterDigitInterval (100 msec): time between generated DTMF digits to PSTN (PBX)
side
Call Termination (Disconnect Supervision) on the FXO Gateway
The FXO Disconnect Supervision enables the gateway's FXO ports to monitor call-progress
tones from a PBX or from the PSTN. This allows the FXO to determine when the call has
terminated on the PBX side, and thereby, preventing analog trunks (i.e., lines to the PBX)
from getting "stuck" when the called phone hangs up.
The PBX doesn't disconnect the call, but instead signals to the gateway that the call is
disconnected using one of the following methods:
Detection of polarity reversal / current disconnect
This is the recommended method. The call is immediately disconnected after polarity
reversal or current disconnect is detected on the Tel side (assuming the PBX / CO
produces this signal).
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3Com VCX V7111 VoIP Gateway User Guide