AT&T Synapse Installation Manual page 24

If your OHP is single-zone, you will have to decide whether it requires an FXS connection or an AUX OUT connection. You can
only connect a multi-zone OHP to an ATA FXS port, i.e. a multi-zone OHP system cannot be connected to the AUX OUT port.
Equipment that can interface with the AUX OUT jack can be "dumb" in its audio output. It doesn't require any exchange of signals
to be ready to broadcast.
Equipment that uses an FXS port must be able to go on and off hook, because the FXS ports use telephone signals to exchange
information. The OHP generally includes some sort of controller or telephone interface, which often requires setting up, for
example, "PABX loop start trunk port access", or "RJ-11 for Tip and Ring connections".
Even though the OHP has no RJ-11 jack, it may still have a Tip/Ring interface, requiring hard wiring. Whenever possible,
try both the AUX OUT jack and an FXS port to find the best configuration for your needs.
There are three possible OHP configurations.
Single-Zone Paging
Single-zone paging means that all speakers connected to the OHP system are activated together (i.e they are in the same zone).
Single-Zone OHP equipment connected to the AUX
OUT jack:
Use this configuration to connect single-zone paging
equipment that uses a 3.5 mm audio jack as input. For
example, use this configuration if the OHP device is
just an amplified speaker. Verify that the OHP input
levels are compatible with ATA level. See
Technical Specifications" on page
zone paging is supported in this configuration.
Installation
Synapse Installation Guide
"Appendix A:
201. Only single-
Figure 9. Single-Zone Overhead Paging on AUX OUT Jack
23