Unlike CTCA, X-Side or Y-Side has meaning only during XID exchange for MPC.

Figure 1 shows that how VTAM® determines which side is the X-side and which side is the Y-side.

In this example, the operator in subarea 1 is the first to activate the link. Because subarea 2 is not active, the XID exchange does not complete. Later, when the operator in subarea 2 activates the link, the XID exchange is completed.