Need to know more ....
Does this occur all the time ?
Can you replroduce the issue ?
When you make a call what happens ?
Does the call try to go thru then fails ?
Does the call actually dial out ?
In bound faxing , does the fax machine ring
Does the line ring and the fax machine not pick up ?
Need to get more info in re to what fails .
How does the fax start working again ?
Unfortunately these are the tough ones . If tis a machine where you cannot get in and log anything , then I am not sure . If you could try and answer some of the above questions , then maybe we can try some station logging , a network trace , to start with . Maybe a trace would be the place to start as it is so intermittant , and tough to find , and the trace can tell you if the call was offhook / ringing / onhook etc .
You may want to open a case ont his one .....