Requirement

Your server must consist of separate listener and application-owning regions. This is because the migration process requires all of the listener regions to be updated before any of the application-owning regions (AORs). If you run composite listener/AORs, which act both as request receivers and request processors, this cannot be done. And if you don't upgrade all the listeners before any of the AORs, your IIOP client applications may receive transient failures during the migration window, depending on the CICS version of the listener region that receives the request.