When a Voice Portal agent makes a call to a PSTN user and the call is routed over an ISDN trunk and if the PSTN disconnects the call before the called party can answer, the PSTN might send an indication to Communication Manager to delay the call drop until the PSTN completes playing an announcement or tone to the caller. The delay in call drop keeps the Voice Portal agent busy while the announcement or tone is being played to the caller, even though the agent cannot actually hear the announcement or tone.

With Communication Manager Release 6.3.6 onwards, you can use the Interworking of ISDN Clearing with In-Band Tones field on the SIP Trunk form to communicate the reason of the call drop to the caller.

After knowing that the called party will not answer the call, the caller or the Voice Portal agent can decide whether to end the call immediately or wait for the announcement or tone to complete.

If you set the Interworking of ISDN Clearing with In-Band Tones field to drop-with-sip-error, Communication Manager sends the reason for the call being dropped by the called party.

If you set the Interworking of ISDN Clearing with In-Band Tones field to keep-channel-active, the call drop is delayed till the complete announcement or tone is being played to the caller.