If you have a network of BTAM terminals connected to a back-level CICS® terminal-owning region (TOR), you will not be able (as you were in previous CICS releases) to route transactions from them to a CICS TS for z/OS®, Version 3.1 application-owning region (AOR). You must either upgrade your terminals or route to a previous version of CICS.
If you have a network of terminals connected by the ACB interface of TCAM to a back-level CICS TOR, you will not be able (as you were in previous CICS releases) to route transactions from them to a CICS TS for z/OS, Version 3.1 AOR. You must migrate your connections to use TCAM/DCB or (preferably) ACF/VTAM, or route to a previous version of CICS. (All terminals that support TCAM/ACB also support ACF/VTAM.)
If you have a network of terminals connected by the DCB interface of TCAM to, for example, a CICS TS 2.3 TOR, you will not be able to migrate the TOR to CICS TS for z/OS, Version 3.1. To do so, you must migrate your connections to use ACF/VTAM.
If you have a network of terminals connected by the DCB interface of TCAM to a back-level CICS TOR, you will (as in previous CICS releases) be able to route transactions from them to a CICS TS for z/OS, Version 3.1 AOR. However, you are recommended to migrate your connections to use ACF/VTAM.