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If the ATLAS FXS ports are configured in the DIAL PLAN, then by default, the FXS ports do not send any signal to indicate the "far end" has hung up. The ports can be configured to remove loop current for a set period of time by configuring the "Forward Disconnect" setting under the DIAL PLAN, USER TERM, in the IFCE CONFIG for the FXS port. The default setting is "Disabled" but this can be set to 600ms, 1000ms, or 2000ms for how long the ATLAS will remove loop current when the "far end" hangs up the call.
So if your Cisco (with the FXO ports) is device A, and it dials device B; when device B hangs up, the ATLAS will then remove the loop current on the FXS port connected to A for however long the Forward Disconnect is configured in order to indicate the call has been disconnected.
Hope this helps,