We got called in by Bendigo Bank Telco to have a look at an ADSL circuit for one of their customers that just wasn’t working. Apparently it had never worked properly since it was connected and “everybody” had looked at it including several times by the carrier, AAPT and there was no improvement.
When our tech arrived on site the ADSL was basically unusable – providing less than 1Mbps on the downstream. The site is in a shopping centre south of Brisbane that is some distance from the exchange so the circuit speed wouldn’t be very good but it should be a lot better than what was being delivered.
First, the modem was exonerated as the cause of the slowness by substituting one of our test modems. This also enabled some data to be gathered as to how the circuit was actually performing. The test modem was moved to the Main Distribution Frame into the shopping complex and another set of tests run. The circuit was OK to there delivering about 4.5Mbps on the downstream so AAPT was right – no trouble in their network.
Where did the problem lie? Somewhere in the internal cable of the shopping centre. The next task for the tech was to locate any Intermediate Distribution Frames that the circuit passed through. Finding frames in a shopping centre can prove quite challenging but in this case the tech was lucky because the IDF was actually in the back corner of the store room of the shop he was working in. Connecting the test modem at that point gave him an unusable circuit again – no different to what was being obtained at the final socket in the back office of the shop.
This meant that the trouble lay somewhere in 40 metres of cable from the MDF to the IDF. Hopefully whatever was causing the trouble was confined to a few pairs and not the whole cable as that would be expensive to fix. Our tech started swapping pairs at both ends to see if he could find a good one. The first few swaps yielded no improvement but jumping towards the higher numbered pairs showed a very worthwhile improvement. After having tried a dozen pairs almost full speed was obtained at the IDF and when the socket was connected, good synchronisation was obtained at a bit above 4Mbps. The customers’ modem was reconnected and the job completed. The customer was very happy as they needed to use that for ordering stock. Judging by the labelling on the socket and the presence of an unused ADSL filter it appears that the previous tenant used a different line for their ADSL and may not have had a problem with it.
The line appeared to be fine for telephony but there was some issue in those 40 metres of cable that was killing the ADSL signal.