Reference:Configuration/FXS/Signaling

The call signalling settings of the analogue TEL interfaces can be adjusted here:

Disable:	Disables the relevant analogue TEL 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).
No Call Waiting:	A checked check box disables the call waiting signal for waiting calls on the relevant interface. Instead, Call busy is signalled to the calling side. This is necessary if, for example, a fax machine is operated on the relevant interface. Note that call waiting is generally only possible if 'feature codes' are enabled for this interface. It might be neccessary to switch on the 'call waiting' functionality explicitly with *43#. This checkmark refuses 'call waiting' even if activated within 'feature codes' and is a safe setting especially for fax machines.
Passive:	Transfers the relevant interface to the passive mode. As a result, the Flash/Hook signal (R key) is not evaluated.
No Call Transfer on Hook-On:	A checked check box disables the call transfer function. Per default calls will be transfered on hook-on. Afterwards a call has been established, this call can be held and a new call can be initiated by pressing the R-Key. If the new call has been established or is yet ringing, the held and new call can be transferred together by hooking on the handset.
Signaling tones audibility:	In normal operation in-band signaling tones are provided like well known from any phone provider. When the a/b is used in conjunction with a DOOR-Interface Converter, it may be desirable that the disconnect signaling tones at the end of a call are not audible to the person at the door. Checking 'in call establishing phase only' does so, but does not suppress the signalling tones in call establishing phase. This implies that the person at the door will hear typical telephone sounds after pressing the doorbell-button. This mode additionally disables recognition of flash (R) pulses. Checking 'never/silent' additionally supresses singalling tones in call establishing phase, so that there will be no audible telephone sounds at all to the person at the door. This mode disables recognition of flash (R) AND DTMFs as well. This might be the typical choice for DOOR-Interfaces.
Wink on peer disconnect:	When the peer side disconnects the call, this can be signaled by a short polarity reversal on the Tip and Ring lines of the a/b port. The duration is configurable in steps of 100ms, 200ms and 300ms. The polarity reversal interval is prematurely stoped by a local side hook-on. Calls disconnected from the local a/b port are not affected. This feature is for special purposes and normally not used.
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.
Metering pulse every:	The gateway can generate periodic metering pulses in fixed intervals of time. The value specified here is the time between two successive pulses. A value of 0 or no value disables pulse generation. Note that metering pulses are only generated for outgoing calls. The first metering pulse is generated when the call is connected. Note also that enabling pulse metering implicitly switches on Passive and No Call Waiting, so that no call can be held and no incoming caller is accepted within a call.