A stack fusion method is implemented at an originator cluster of software services in a distributed Software-as-a-Service (SaaS) system. The method includes receiving a request for a communication service from an originator registered to the originator cluster. The method further includes, responsive to the request, creating a communication protocol object in the originator cluster, discovering a participant cluster on which the participant is registered, notifying the participant via the participant cluster that the communication protocol object exists, and updating an index protocol object in the participant cluster that tracks communication sessions in which the participant is engaged with a reference that points to the communication protocol object in the originator cluster.