CICS® Transaction Server for Windows, CICS on Open Systems, and CICS/400 support only the minimum level of BMS. (They support SEND TEXT.)
The mapping operations of BMS are performed in the system on which the user’s transaction is running; that is, the application-owning system. The mapped information is routed between the terminal and this transaction via the relay transaction, as for terminal control operations.
When transaction routing with BMS, you should be aware of the limitations of BMS, and of the possible different levels of support in the application owning region and the terminal owning region when they are running on CICS systems on different platforms.