fax connection to FXS port

Unanswered Question
Jan 8th, 2009
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I have a fax machine connected to an FXS port on an MGCP gateway. It works ok with the exception that it takes exactly 45secs to free itself up to take the next call after the call has finished.

I have looed at the timers on the gateway voiceport and looked at some service paramters to see where this 45 secs delay is.

Is there anywhere I can change this delay so I can reduce it or is it possibly a fax machine issue itself



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Rob Huffman Thu, 01/08/2009 - 05:37
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Hey Paul,

Happy 2009 my friend! Just a guess here (sorry) :)

Supervisory Disconnect

The Supervisory Disconnect feature provides a disconnect indication to the remote party in a two-party call after one side disconnects. This enables external applications connected to the Cisco voice gateway to promptly clear a call after receiving the disconnect indication. This feature triggers a power denial on FXS ports with loop-start signaling when a voice call disconnects. The power denial is only generated in a two-party call scenario when one party disconnects. Power denial is not generated if a call is on hold and either the active party or the on-hold party hangs up. Power denial is also not generated for a three-way conference call when one party hangs up. This feature is enabled and disabled on a voice port basis. The remote party receives the power denial signal for the duration that is set on the analog FXS port.

Configuring Supervisory Disconnect


Hope this helps!


bigcappa1 Thu, 01/08/2009 - 06:11
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And a Happy 2009 to you Sir.

I tried the Supervisory Disconnect and the Call Disconnect and even amended the Wait release timeout (not all at the same time). All these were set to the defaults and this did not help

I also had a look at some of the general MGCP settings in the CM service paramters again no change, there was only one that I could see affects Fax.

It seems strange it is exactly 45 seconds for the FXS port to clear once the call is disconnected. But thanks once again for your valid input, at least we were looking in the same direction



Nicholas Matthews Thu, 01/08/2009 - 06:42
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Hi Paul,

This may be something the fax machine does. The fax machine may just not actually go on-hook until 45 seconds later. I would use a combination of 'show voice call summary' and 'show voice port summary'. You'll see there whether or not the fax machine is actually back on-hook or not.

My guess is that you'll see that the fax machine is actually off-hook and it's a guard-out mechanism of the fax machine itself. On something like this FXS port I wouldn't expect a timer to keep it for 45 seconds.



bigcappa1 Thu, 01/08/2009 - 07:11
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Thanks think I tend to agree it is the fax

Dialing FAX Machine. Reviewed it with the suggested commands and it appears that that way

Thanks for the help



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