It looks like a caller is on hold after they hang up

Updated by Johnny Goldsmith


This document covers the Hx6 and iQ6 phone systems in regards to when the unit is not dropping callers that actually hang up while on hold


A caller is put on hold to go on the air. But while waiting on hold the caller decides to hang up. However, the VSet or call controller appears to show that the caller is still on hold.

The line the caller was on is then brought to air, but only a dial tone or off-hook tone is heard.

Solution and Explanation

In POTS (Plain Old Telephone Service) telephony, there are electrical signals that indicate the status of the phone line at any given time.  These signals control what your device does and what the equipment at the telephone company does when someone does something, like pick up or hang up the phone.

On an idle line, there is 48 Volts DC on one of the wires.  When someone picks up the phone, a load is placed on the line that makes this 48V signal drop to around 10V telling the phone company that someone has picked up the phone.  The telephone company will then reply with a dial tone. As long as this voltage is present, the Hx6 will think that there is a call on the line. 

When the person at the other end hangs up, the telephone company should make this voltage drop all the way to zero volts for about a half-second and then bring it back up again.  This tells the Hx6 to drop the line automatically.  This momentary removal of loop current is called Calling Party Control or CPC for short.  If it does not occur, the Hx6 will not automatically drop the line.

Auto Drop Setting

You can ensure that Auto Drop is set on the Hx6 and iQ6 from either the front panel or the web UI.

Front Panel

On the menu select TELECOM > POTS > ADVANCED > AUTO DROP.  It should be set to LOOP AND CPTD in order to respond to these signals. 

Web User Interface

Under the Telco tab, make sure Enable Auto Call Drop is set to Both Loop Drop and CPTD.

You can also adjust the value next to CPC DELAY.  Its default setting is 250ms, which should be adequate. However, you can try decreasing it to see if it makes the problem better.   

If these settings don't help, we suggest reaching out to your phone provider and telling them that you need CPC signaling sent when the far end hangs up the phone.

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