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Community Member

FXS port is up, on hook, FAX number returning slow busy

We have a remote CUCM 7 and an MGCP gateway with an FXS port configured for a FAX machine.

This worked fine up until yesterday.

These questions are mostly for my understanding of what is happening here:

The FAX number when called is returning slow busy.

I can see the call hitting the gateway when the number is dialed from an outside number.

There should be no config changes.

I have done a "sh/no sh" on the voice port.

The FXS port is shown below:

Foreign Exchange Station 0/1/0 Slot is 0, Sub-unit is 1, Port is 0
Type of VoicePort is FXS  VIC-4DID
Operation State is DORMANT
Administrative State is UP
No Interface Down Failure
Description is Admin FAX

Noise Regeneration is enabled
Non Linear Processing is enabled
Non Linear Mute is disabled
Non Linear Threshold is -21 dB
Music On Hold Threshold is Set to -38 dBm
In Gain is Set to 0 dB
Out Attenuation is Set to 3 dB
Echo Cancellation is enabled
Echo Cancellation NLP mute is disabled
Echo Cancellation NLP threshold is -21 dB
Echo Cancel Coverage is set to 64 ms
Echo Cancel worst case ERL is set to 6 dB
Playout-delay Mode is set to adaptive
Playout-delay Nominal is set to 60 ms
Playout-delay Maximum is set to 1000 ms
Playout-delay Minimum mode is set to default, value 40 ms
Playout-delay Fax is set to 300 ms
Connection Mode is normal
Connection Number is not set
Initial Time Out is set to 15 s
Interdigit Time Out is set to 10 s
Call Disconnect Time Out is set to 60 s
Supervisory Disconnect Time Out is set to 750 ms
Ringing Time Out is set to 180 s
Wait Release Time Out is set to 30 s
Companding Type is u-law
Region Tone is set for US

Analog Info Follows:
Currently processing none
Maintenance Mode Set to None (not in mtc mode)
Number of signaling protocol errors are 0
Impedance is set to 600r Ohm
Station name None, Station number None
Translation profile (Incoming):
Translation profile (Outgoing):

Voice card specific Info Follows:
Signal Type is loopStart
Ring Frequency is 25 Hz
Hook Status is On Hook
Ring Active Status is inactive
Ring Ground Status is inactive
Tip Ground Status is inactive
Digit Duration Timing is set to 100 ms
InterDigit Duration Timing is set to 100 ms
Hookflash-in Timing is set to max=1000 ms, min=150 ms
Hookflash-out Timing is set to 400 ms
No disconnect acknowledge
Ring Cadence is defined by CPTone Selection
Ring Cadence are [20 40] * 100 msec
Ringer Equivalence Number is set to 1

I have a few questions:

Whenever a fast busy or slow busy is returned to the caller, is call manager providing both of these signal?

Slow busy would make sense, but I am not sure about fast busy.

So it is  a slow busy, and I see no change in the port (dormant, on hook), could the FAX machine be a problem with these symptoms?

Is there a way for me to test the port remotely and get a ring or dial tone?


Re: FXS port is up, on hook, FAX number returning slow busy


Just wondering if you have ISDN or FXO connectivity to the PSTN. if its former, could you please provide the output from debug isdn q931 while you make an attempt for fax.

Also, could you please paste the relevent configuration from the router

I guess it looks like a dial-peer issue.


Sam Wilson

Community Member

Re: FXS port is up, on hook, FAX number returning slow busy


Thanks for the reply, I am not too familiar with voice, so forgive the basic questions.

This router has a PRI attached via a VWIC card and is ISDN. The branch uses the WAN for branch to branch calls and the PRI is used for anything outside our network.

I did a debug q931and I can see the call from my cell hitting the gateway, is there anything in particular I could look for in the debug that?

I did a "sh dialplan n" and the dial-peer was hit, also this is a slow busy, not a fast busy.

Correct me if I am wrong, but if there was no dial-peer available, wouldn't I get fast busy?

Even though the gateway is configured to use MGCP, does the gateway still have to have dial-peers configured to ensure proper forwarding of calls to and from the PRI?

Also, when receiving either fast or slow busy, is call manager telling the phone to provide both of those to the end user?

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