ADSL Customer with Rain-Related Sync Drops and a Refund Demand
A customer on an 8 Mbps ADSL2+ plan calls to say the internet is 'useless': a speed test on his phone shows 1.8 Mbps, and the modem drops sync for a few minutes whenever it rains. The line is 3.8 km from the DSLAM. The modem status page shows downstream attenuation 57 dB, downstream SNR margin 5.8 dB, upstream 6.1 dB, CRC errors climbing by about 1,200 per minute, and an attainable rate of 3.2 Mbps. The premises has 15-year-old internal wiring with one taped joint behind a cupboard and three parallel telephone sockets, each fitted with an operator-supplied filter. The customer insists the fault is in the exchange and demands a refund for three months. A previous visit changed the modem and the splitter with no improvement.
1. Is the fault most likely in the exchange, the access cable, or the customer's internal wiring? What does the rain correlation tell you, and which measurement is most diagnostic?
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The evidence points to the copper access path, with internal wiring as a strong secondary suspect - not the exchange core.
- 57 dB attenuation at 3.8 km is high but not impossible for that length; it means the line is already near the edge of 8 Mbps service.
- 5.8 dB SNR margin at 3.2 Mbps attainable means the modem has trained down to stay stable. That is a line-condition problem, not a plan-provisioning problem.
- CRC errors at 1,200/min with sync drops are physical-layer errors: noise, bad joints or water ingress. Errors, not just low speed, are the diagnostic signal.
- The rain correlation is the strongest clue. Rain does not affect the exchange; it affects outdoor joints, closures, drop wire and cable pits where moisture enters. A taped joint behind a cupboard is also a classic bridge-tap and noise source.
- The phone speed test is not diagnostic because it includes Wi-Fi. Only a wired LAN test at the modem, plus modem line statistics, should be used.
So: exchange port statistics first (to rule out a congested or faulty port), then the access cable, then the internal wiring - in that order, isolating at the demarcation point.
2. Give the sequence of tests you would run, and the decision point at which you escalate to the line team rather than charge the customer for internal wiring.
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Sequence:
- Pull DSLAM port data remotely: current sync rate, SNR margin history, CRC/ES counts, and whether other lines on the same cable show errors. If neighbours are clean, the problem is local to this line.
- Test from the NTP/demarcation point with a known-good modem and a short patch lead, wired LAN only. Record sync rate, attenuation, SNR margin and error counts for 10–15 minutes.
- If the line is clean at the demarc, the fault is internal: taped joint, bridge tap from the third socket, faulty filter, or unfiltered device. This is chargeable customer wiring work; quote before doing it.
- If the line is still poor at the demarc, escalate to the line team with the readings. A joint or closure exposed to rain, or a wet pit, is network-side and must be repaired at operator cost.
Decision point: the demarcation point. Clean at demarc = customer side; dirty at demarc = operator side. Do not decide from the phone speed test, and do not accept 'we changed the modem' as evidence, because the modem was never the failing element.
3. Write what you would tell the customer about the cause, the next step, and what you can and cannot promise, including the refund demand.
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A workable script: 'Your line is syncing with a lot of errors, and the errors get worse when it rains, which usually means moisture in an outdoor joint or a problem in the old internal wiring. The modem and splitter have already been changed, so we are not replacing them again. We will test at the point where our line enters your house. If the line is clean there, the fault is in the internal wiring - the taped joint and the extra sockets - and we will give you a written quote before touching it. If the line is bad there, it is our responsibility and our line team will repair it at no cost.'
On the refund: do not promise one at the doorstep. Explain that the account will be reviewed against the actual fault location and downtime records, and that a credit will be raised if the fault is ours. Be specific about the appointment window and the ticket number.
Do not promise 8 Mbps. At 57 dB attenuation the line will never deliver 8 Mbps; offer a realistic profile or a lower-tier plan rather than leave the customer measuring a speed the copper cannot carry.