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IMG 1010 - Overlap Signaling - Receiving

By default, the IMG passes digits to the outbound side as they are received. If the outbound channel group does not support Overlap Signaling (SIP, H.323), enable overlap signaling on inbound channel groups. Overlap Signaling is enabled in the IMG 1010 - Channel Group pane.

When Overlap signaling is enabled, the IMG will collect address digits until a Termination Condition is met and then continue call processing. See below for protocol-specific information.

Overlap is only applied to the inbound channel, even on an Incoming/Outgoing Trunk.

SS7

When Overlap Signaling is enabled, the IMG will collect digits until one of the following termination conditions is met:

  • Termination Digit Received (default = #)

  • Minimum # of Digits

  • Inter SAM Timeout

  • Total Overlap Timeout

Overlap needs to be enabled for inbound SS7 SAM digits only if the outgoing side is IP or SS7 ANSI.

Example Call Flow

Euro ISDN (E1)

When Overlap Signaling is enabled, the IMG will collect digits until one of the following termination conditions is met, and then send CALL PROCEEDING and attempt to route the call.

  • Minimum # of Digits Received. - The value chosen should be equal to or greater than the maximum number of digits expected

  • Total Overlap Timeout

  • T302 Timer Expiry (Wait for INFO ISDN Timer)

  • Reception of an INFO message with a Sending Complete Information Element

  • Reception of a SETUP message with a Sending Complete IE

  • Inter SAM Timeout

The time the IMG will wait for an indication from its internal ISDN layer that an INFO message has been received. This value should be greater than 15 seconds. If the Inter SAM Timeout value is less than 15 seconds and expires before T302, the IMG will send CALL PROCEEDING and attempt to route the call with the digits it has at that point

All of these except the T302 Timer are configured in the ISDN Group pane. The T302 Timer is not configurable and per specification is set at 15 seconds.

If a call is received and T302 expires, Cause 28 will be sent to the network. Should you choose to make your Inter SAM Timeout smaller than 15 seconds you will attempt to process calls with most likely less than the number of digits you want. It is incumbent on the side that is sending you digits to send a Sending Complete IE to indicate the sending of digits is completed.

Overlap needs to be enabled for inbound ISDN INFO digits only if the outgoing side is IP or SS7 ANSI.

 

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