The gateway is responsible to detect and notify the peer side of the call
when the remote party is disconnected. This function is called disconnect
supervision. This section explains the attributes that controls how the
gateway detects PSTN call disconnect.
By default the carrier does not notify the FXO port when the remote party
is disconnected. In such case the gateway could be configured to
disconnect the call when one if the following conditions occurs:
- Silence detection is when the gateway detects the silence for a
specified period of time - not supported in this version of the gateway.
- Tone detection is when the gateway detects specific tones (dial,
busy, reorder or sit)
However, it is possible to ask the carrier to provide feed-back when the
remote end is disconnected. The following modes exist:
- Battery removal (also called forward disconnect and kwelstart) is
when the PSTN provider removes the battery current from the analog line
for a period of time. This mode is prevalent in North America.
- Reverse battery (also called reverse polarity) is when the PSTN
provider reverses the polarity of the battery voltage.
- Disconnect tone is when the gateway detects a specific disconnect
tone (for example: 440Hz).