The XA support of CICS TG V6.1 builds on top of the transactional EXCI support by providing global transaction support for requests to CICS via the new CICS ECI XA resource adapter.

Out of these possible options, the only protocol that supports two-phase commit transactional coordination for ECI flows is the External CICS Interface (EXCI).

CICS TG on z/OS makes use of the EXCI to provide high speed cross memory access to CICS, a mechanism not available on other platforms as it is an MRO-based communications mechanism.