# Fault Tolerance with Load Balancing

You can configure Substation ES to talk to one or more Enterprise Message Service servers, a Fault Tolerant (FT) Enterprise Message Service pair, or both, and configure each of them separately within a single address space.

Substation ES, which runs as a separate address space in z/OS, communicates with Enterprise Message Service servers and hence operates as an Enterprise Message Service client.

The CICS and IMS interfaces enable Substation ES to talk to one or more BESs, making for many possible configuration permutations as shown in the following figure:

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