In IBM mainframes, a Cross-system Coupling Facility, or XCF, is a component of z/OS that manages communications between applications in a sysplex.
Systems communicate using messages transported by one of two mechanisms: In a parallel sysplex decisions about which of these two transport mechanisms to use for routing a specific message are made dynamically.
Applications join specific groups as individual members.
On joining a group a member can send or receive messages.
Each transport class owns input and output buffers.