Collecting ISDN Digits and Sending Complete Number in SIP
The device can support an overlap dialing mode whereby the device collects the called party number digits from ISDN Q.931 Information messages or DTMF signals, and then sends a SIP INVITE message to the IP side containing the complete destination number.
ISDN overlap dialing for incoming ISDN calls can be configured for the entire device or per ISDN trunk. This is configured using the global parameter, [ISDNRxOverlap] or the [ISDNRxOverlap_x] parameter (where x denotes the trunk number), respectively.
By default (see the [ISDNINCallsBehavior] parameter), the device plays a dial tone to the ISDN user side when it receives an empty called number from the ISDN. In this scenario, the device includes the Progress Indicator in the SetupAck ISDN message that it sends to the ISDN side.
The device can also mute in-band DTMF detection until it receives the complete destination number from the ISDN. This is configured by the [MuteDTMFInOverlap] parameter. The Information digits can be sent in-band in the voice stream, or out-of-band using Q.931 Information messages. If Q.931 Information messages are used, the DTMF in-band detector must be disabled. Note that when at least one digit is received in the ISDN Setup message, the device stops playing a dial tone.
The device stops collecting digits (from the ISDN) upon the following scenarios:
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The device receives a Sending Complete IE in the ISDN Setup or Information messages, indicating no more digits. |
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The timeout between received digits expires (configured by the [TimeBetweenDigits] parameter). |
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The maximum number of received digits has been reached (configured by the [MaxDigits parameter]). |
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A match is found with the defined digit map (configured by the [DigitMapping] parameter). |
Relevant parameters (described in PSTN Parameters):
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[ISDNRxOverlap_x = 1] (can be configured per trunk) |
To configure ISDN overlap dialing using the Web interface, see Configuring Trunk Settings.