On the fault graph, the symptoms you see are some very minor yellow peaks - showing that the maximum latency gets rather higher than normal, but not in any particularly continuous way, and with no special change during the evening peak hour
For comparison, here's mine
. Note the evening peak - which is down to traffic at the ISP or on the WBC backhaul, not my link at all.
Note, especially, that your blue areas *don't* change in the same way as the yellow. That means the delays are happening to individual packets, on an occasional basis, keeping the average delays low.
[Detailed maths: My estimation is that your yellow mini peaks represent about 15ms delay, and that 1 horizontal pixel represents 100 seconds. That means at least 1 ping in 100 is getting delayed by 15ms, and the average additional delay is 0.15ms. When it gets to 7 pings in 100 delayed by 15ms, the average increases to 1ms - and the blue line moves 1 pixel higher.]
So yellow peaks alone mean 1-3 packets in 100 are being delayed by 15ms. Yellow peaks with a single extra pixel in blue means around 7 packets in 100 are being delayed by 15ms.
Conclusion: Every ping packet is getting to the modem, and 95%+ are getting back in the minimum latency. Even when there are delays, it only affects 10% or so of packets, by up to 15ms.
Like R0nski, I think this suggests that something else is transferring, that causes the ping packets to be queued slightly. But the queue could be happening *anywhere* between TBB and your router (or whatever you have responding to the ping).
The one place that wouldn't queue your ping packets is the modem (your modem or the cabinet's modem), at least due to errors: Errors in the modem-modem stream cause packets to be dropped, never queued. The modem probably could queue the ping due to QoS, but that would be triggered by some other download/upload happening.
Note, especially too, that there are no red areas - there is zero packet loss. Because ping packets are never retried (by design), and you can see zero loss, you know for certain that they aren't being lost on the modem-modem link either.
No red areas also means no resync's, for any reason at all. DLM hasn't intervened to turn anything on or off, and there has been no independent loss of signal.
On that evidence, there is *nothing* wrong with the copper.
There could be something wrong with your modem, that make it *look* to be working perfectly. For example, that it is responding perfectly to pings but choosing to delay or drop your downloads, but that would be a very individual fault. Seems unlikely to me.
on your "working normally" graph, you get a blip of reduced latency.
There is no packet loss, so there have been no resyncs to cause this. Either we blame this on a brief re-routing of packets within BT's 21CN WBC network, or we suspect something with your modem.
It is hard to believe that your modem has a fault that just happens to manifest itself by appearing to work perfectly on the TBB Ping graph.