Zyxel LTE-3316-M604 busy tone



I have setup the Zyxel LTE-3316-M604 4G modem router and am making use of the built in analogue telephone adapter (ATA) with some DECT cordless phones.

It is all registered fine with the SIP provider and working behind the NAT with no special firewall rules and SIP ALG disabled and no STUN server set.

However, I have noticed that if a caller calling in disconnects first, then the Zyxel remains in a n 'off hook' state and subsequent attempts to call in get either silence or a busy tone.

I have checked this is not an issue with the SIP provider and they have confirmed it is not and the Zyxel is sending busy.

If the Zyxel end phone user hangs up first, there is no issue here.

Disconnecting and reconnecting the phone to the Zyxel does not clear this, only thing that does is a restart of the Zyxel

I have applied the latest firmware of V2.00(ABMP.7)C0 although interestingly from the Sip server this identifies as V2.00(ABMP.6)C0

Any help to diagnose this would be appreciated. I am in the uk using Andrews & Arnold as sip provider.

The region setting on the Zyxel for voice is set to USA and unable to change this.


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