3Com TP-1610, Usermanualmanual, Page: 280 / 496

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V6100 and V7122 User Guide
ISDN Overlap Dialing
Overlap dialing is a dialing scheme used by several ISDN variants to send and / or receive
called number digits one right after the other (or several at a time). As opposed to en-bloc
dialing in which a complete number is sent.
The V7122 can optionally support ISDN overlap dialing for incoming ISDN calls for the entire
gateway by setting ‘ISDNRxOverlap’ to 1, or per E1/T1 span by setting ‘ISDNRxOverlap_x’
to 1 (‘x’ represents the number of the trunk, 0 to 7).
To play a Dial tone to the ISDN user side when an empty called number is received, set
‘ISDNINCallsBehavior = 65536’ (bit #16) causing the Progress Indicator to be included in the
SetupAck ISDN message.
The V7122 stops collecting digits (for ISDN
Æ
IP calls) when:
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The sending device transmits a ‘sending complete’ IE in the ISDN Setup or the following
INFO messages to signal that no more digits are going to be sent.
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The inter-digit timeout (configured by the parameter ‘TimeBetweenDigits’) expires. The
default for this timeout is 4 seconds.
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The maximum allowed number of digits (configured by the parameter ‘MaxDigits’) is
reached. The default is 30 digits.
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A match is found with the defined digit map (configured by the parameter, DigitMapping).
Relevant parameters (described in Table 52 ):
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ISDNRxOverlap
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ISDNRxOverlap_x
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TimeBetweenDigits
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MaxDigits
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ISDNInCallsBehavior
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DigitMapping
Using ISDN NFAS
In regular (non-NFAS) T1 ISDN trunks, a single 64 kbps channel carries signaling for the
other 23 B-channels of that particular T1 trunk. This channel is called the D-channel and
usually resides on timeslot # 24.
The ISDN Non-Facility Associated Signaling (NFAS) feature enables use of a single D-
channel to control multiple PRI interfaces.