I was helping one of my remote clients with a intermittent ADSL fault. I thought I would write it up as it covers a lots of the basic problem solving techniques.
Description of the Fault: Between 18:00 and 8am the router would go offline completely. However during office hours the connection stayed up.
So we have a consistent set of circumstances (always good when problem solving).
What we did.
The end user was remote so I haven’t actually been to his site, so the pre-configured router I shipped might have not been micro filtered properly at his end.
So we go into an in-depth conversation about what is plugged into what.
I get a detailed map written down on a bit paper. Sometimes its easy to mix up a telephone double adaptor with a micro filter to most users they look very similar.
From his description it sounds like its correct. So why does it go offline during that period.
So I remotely connect to the routers management page and look for signs of a bad connection. Either a SNR or Loop value.
The connection is slow but this can be accounted for by the users distance from the telephone exchange.
Sure enough come six o’clock the router gets kicked offline.
So we contact the ISP and get them to run a line test, which passed ok.
So back to problem solving on site.
Tech Tip: Next up was to remove all other telecommunications equipment from the sockets, leaving only the router plugged into a micro filter plugged into the wall. This would eliminate any other in-house interference.
Once again come six o’clock boom, it goes offline.
So we arrange for the ISP to do another line test during the outage period.
They report back it failed a copper line test, which would indicate a PSTN fault and problem with the line going into the customers premises.
So the following day when the system was working another line test was done, which also failed. So we then get a BT engineer to site. They rewire the line coming in to the premises and the problem is solved.
Conclusions
The weird on/off nature of this problem was confusing and misleading. The faulty external telephone cabling must have been picking up some interference from something like a nearby street light or something that was active during those periods.
We did 3 line tests at the ISP 1 passed, 2 failed. So inconsistent results again the initial pass took the problem solving off course for a bit.
The problem is now fixed but it did cause some head scratching for a bit.