Reference10:Interfaces/FXO/Signaling

The call signalling settings of the analogue FXO interfaces can be made here:

Disable:	Disables the relevant analogue FXO interface.
Speech Bearer Capability:	Calls on the relevant interface are transmitted with Audio Bearer Capability as standard. A checked check box transmits calls from the relevant interface with Speech Bearer Capability. This only makes sense if only telephones are operated on the relevant interface (no fax machine or modem).
Central Office Tone detection:	When the FXO initiates a call, normally a audible tone is expected to be received from the central office/local PABX side. The tone detection works independantly from any country setting. When th expectred tone cannot be detected within 2.6sec, then the call will be cancelled. If this tone detection is disabled, the FXO will continue with dialinga the configured number via dtmf regardless of any tone recaived with a delay of 800ms after hook-off.
Alert Tone detection:	After the configured nuber has been dialed, the FXO normally waits for a audible response from the dialed side that can be identified as an alerting tone. The proper detection and analysis of this tone takes up to a few seconds. If you additionally enable the Assume alert option, the detection is simplified and therefore reduced to a simple tone detection. This means that an alert will be regarded as detected even when any sort of tone or rhythm is detected. This is much faster than the exact analysis and normally has no negative effect. When alert is detected, the voip>-FXO->peer connection is connected, so that the voip peer initiator of the call now can hear the alerting tone from peer side. Disabling Alert Tone detection will directly connect the calls, which is much faster.
Assume Alert:	see previous topic for details. Assume Alert has no effect when Alert Tone detection is disabled.
Volume:	Sets the volume for the relevant interface, in decibel (dB), between -32dB and +32dB. No value or the value 0 is equal to the factory settings.
CallerID 1 standard:	Selects the standard in which CallerID is detected and decoded. What is of interest here is the caller's phone number in case of an incoming/ringing call. This number is fed into the resulting voip call as the CGPN (Calling Party Number). Note that for this reason the FXO port has to be registerd to the PBX as 'gateway', and has to be configured with 'force enblock' in the Routes Menu. The FSK standards can contain additional information like 'Called Line Id' or 'Date/Time' information. These additional informations will be dropped. The DTMF standards anyway only contain the 'Calling Line Id'.