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Fax Sending Problems with One Specific Number

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Fax Sending Problems with One Specific Number


This article will provide you with information on how to capture the needed information to correctly analyze the problem at hand. It’s not designed to provide 1 specific solution for this problem but can help you to pinpoint the exact cause in your specific case.

It consists out of 2 parts. The first part will “only” provide you with a short list of what’s needed while the second part will provide you with some extra information and references.

First Part:

When you have issues with reaching one (1) specific fax number, please enable the following traces and settings in order to fully analyze the problem.

  • Gather information about the receiving fax machine. (Make, model, type…)
  • Activate TCOSS, ISDN, MODEM and BINARY traces.
  • Set config line 251 to “84 80 81 C4 C0 C1”. Disregard the quotation marks.
  • Send faxes with different speed and ECM settings.
  • Send all the captured traces + a detailed description of the test performed to your next level of support.

Second Part:

It can occur that you have problems reaching just one (1) specific fax number. This can have several causes:

  • Receiving side has a bad line quality
  • Receiving side is using old or incompatible hardware
  • Receiving side doesn’t have a fax machine
  • Either side is not complying with the fax protocol…

To eliminate some of these reasons from the get-go it’s important to gather some information about the receiving fax machine (Make, model, type…)

Possible errors that can occur:

  • No Fax machine detected (XL)
  • Illegal identification of called station (XM)
  • Illegal response during training phase (XN)
  • Three learn attempts unsuccessful (XO)
  • Illegal page confirmation (XP)
  • Unable to find appropriate baud rate (XS)
  • No response received (XT)

Please check chapter “Two Character Error Codes” in the current “TCOSS system manual” for more information on these and other errors.

First thing that needs to be done is to activate tracing. Activate TCOSS, ISDN, MODEM and BINARY traces. Please refer to “Fax tracing – quick reference” or “Tracing fax communication problems” for more information.

To not increase the load on the system unnecessarily, you should enable these trace settings only on one channel and reroute send orders to that specific number via the channel with traces enabled, e.g.


F:000123456789~,04:000123456789~ , assuming that channel 04 is the channel with the traces enabled.

In addition to activating these traces also a channel configuration change needs to be made. Set configuration line 251 to this value: “84 80 81 C4 C0 C1”. Disregard the quotation marks.

3617 Screen Shot 2018-07-24 at 10.19.04 AM.png

A reboot of the Node is required after making these changes. Also note that this setting is now used for all outgoing faxes which are sent via this ISDN Line.

For more information about the usage of this config line check out chapters:

  • “5.5 – Higher/Lower Layer Compatibility Settings (EuroISDN and QSIG)” in the “TCOSS ISDN Reference” manual.
  • “4.9.1 – Troubleshooting” in the “TCOSS Configuration Manual”.

Now you can start to perform some tests. Use at least a 5 page document with complex content as your test document. Sending only a one-line test message will possibly not report the same problems as recognized for productive messages sent to this number.

First just try to send a fax to the problematic number. If this fax goes through it will probably be “just” a ‘higher capabilities issue’.

If the fax doesn’t go through you’ll have to perform some more tests by sending faxes at lower/different speeds and with/without ‘Error Correction Mode’ (ECM).

This can be accomplished by adding a couple of parameters in front of the fax number.

In the screen shot below you can see 1 character and 2 digits after the service and before the fax number.

3617 Screen Shot 2018-07-24 at 10.21.26 AM.png

Recommended combinations to try:

  • N00, N10, N20, E10, E20, E30

Please document the result for each setting.

For more information about these test settings please check chapter: “ – Mode Selection for Transmission” in the current “TCOSS system manual”.

Now gather all captured traces and provide them together with a detailed description of the issue and the performed tests, to your next level of support.


Level of Complexity 


TC/SP 7.80.04 – Current (article based on TC/SP 7.86.00)


Applies to  

Product Version Build Environment Hardware
TC/SP 7.80.04-     Current (article based on TC/SP 7.86.00)  


Recommended extra documentation to have at hand:

  • KB article: “Fax tracing – Quick reference”
  • KB article: “Tracing Fax Communication problems”
  • TCOSS System Manual
  • TCOSS Configuration Manual
  • TCOSS ISDN Reference


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