Core Issue
In the Cisco CallManager 4.x environment, which is integrated with Avaya 8300, normal calls works fine and when a confrence call is initiated the call drops immediately. Also media gateway server shows the Temporary Failure error message.
Resolution
This issue occurs when Media Termination Point (MTP) option in the H323 GW config in CCMAdmin page is not checked. In order to resolve this issue, check the MTP in order to have the supplementary services.
Refer to Media Termination Point Configuration for more information about the MTP.