No Ringback to PSTN when IP Phones has Cfwdall enabled

Unanswered Question
Jul 16th, 2007


We are facing a problem in H323 gateway.

When receiving a call via the ISDN PRI line inbound to an extension on IP phone CfwdAll (Call Forward All) set, the PSTN caller does not hear ringback.

The call will complete and connect with the phone forward too, however during the call forward connection setup there is no ring back.

All other ringback is proper, only calls to extension with CfwdAll set, and only with the inbound over the ISDN PRI local access line.

If a call comes in over the Inter-company VPN CAS-T1 line, to an extension with CfwdAll set, ringback is heard by the caller.

I researched a few hundred Cisco Web site listings through searching "no ringback", but did not find anything that directly relates to this issue, it appears to be with the ISDN line only. Most descriptions related to a system wide issue.

The CCM cluster is on MSC-7835 operating CCM 4.1(3)sr5b

I have 3 location operating off this CCM cluster, the only location with this issue is the 3825 gateway, and only on inbound calls through the ISDN PRI line.

Please help.


I have this problem too.
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jbayuka Fri, 07/20/2007 - 12:14

Early alerting is prevented in these ways:

For calls terminating at an ISDN switch?The terminating gateway sends an Alert message to the originating gateway only after it receives an Alert message from the terminating switch.

For calls terminating at a CAS switch?The terminating gateway sends a Progress message to the originating gateway, instead of an Alert message, after it receives a Setup message.

This URL should help you:


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