290 V7122 GatewayUser GuideISDN Overlap DialingOverlap dialing is a dialing scheme used by several ISDN variants to send and / or receivecalled number digits one right after the other (or several at a time). As opposed to en-blocdialing in which a complete number is sent.The gateway can optionally support ISDN overlap dialing for incoming ISDN calls for theentire 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 theSetupAck ISDN message.The gateway stops collecting digits (for ISDNÆIP calls) when: The sending device transmits a ‘sending complete’ IE in the ISDN Setup or the followingINFO messages to signal that no more digits are going to be sent. The inter-digit timeout (configured by the parameter ‘TimeBetweenDigits’) expires. Thedefault for this timeout is 4 seconds. The maximum allowed number of digits (configured by the parameter ‘MaxDigits’) isreached. The default is 30 digits. A match is found with the defined digit map (configured by the parameter, DigitMapping).Relevant parameters (described in Table 45): ISDNRxOverlap ISDNRxOverlap_x TimeBetweenDigits MaxDigits ISDNInCallsBehavior DigitMappingUsing ISDN NFASIn regular (non-NFAS) T1 ISDN trunks, a single 64 kbps channel carries signaling for theother 23 B-channels of that particular T1 trunk. This channel is called the D-channel andusually resides on timeslot # 24.The ISDN Non-Facility Associated Signaling (NFAS) feature enables use of a single D-channel to control multiple PRI interfaces.
