When it was first fitted the Thinkbroadband Speed Tests reported very low speeds, the browsing was dire and web pages failed to load so I contacted Zen Technical Support and the Technical Support person said not to use the Thinkbroadband site for speeds test because of the high speeds involved and to use this speed test site; https://zen-internet.speedtestcustom.com/
The first recorded test on that site at about 4:00PM in the afternoon gave a ping of 19, a jitter of 54, a download speed of 145 Mbps and an upload speed of 95 Mbps - oops
The next recorded test on that site at about 20 minutes later gave a ping of 19, a jitter of 1, a download speed of 123 Mbps and an upload speed of 9 Mbps.
The next test about 42 minutes after the first gave a ping of 12, a jitter of 1, a download speed of 326 Mbps and an upload speed of 110 Mbps.
Since then the reported ping on that test site has been between 11 and 13 and the reported jitter has been between 0 and 2, the download speeds have been between 904 Mbps and 88 Mbps, and the upload speeds have been between 50 Mbps and 111 Mbps. - (On average the Upload speeds tend to be over 100 Mbps irrespective of the major variations in the download speeds).
The speeds vary at unspecified times of the day and I am just as likely to get over 800 Mbps at 9:00PM at night as I am to get 312 Mbps at 4:00AM in the morning.
Regarding my copper line quality: up to three months ago, my copper line was about 725 meters long, (as was reported by my router), my router never lost sync, my sync speed was up to 53 Mbps with a SNR, set by the DELSLAM/DLM of 3db. and a flat line Thinkbroadband Speed Test Graph of around 47 Mbps with zero unrecoverable CRC errors on the router or at the exchange reported. - Three months ago, we had one of those Openreach Engineer changes at just after 2:00AM in the morning, (probably to fix someone else's fault), when the line went off and came back much worse with a reported length of 740 meters, no router errors, about 200 exchange errors per day and about 12 unrecoverable CRC errors per week. - The speeds went down the toilet but after a profile reset about a month ago the sync speed had gone back up to 47 Mbps, the flat line graph speed tests were back to around 44 Mbps and the SNR had dropped back down from 8db. to 5db., there were still zero Router Errors reported, there were still around 200 Exchange Errors reported per day and there was still about 12 unrecoverable CRC errors per week. - (We use the higher rated Fritzbox 7590 which kept a good weekly record of the DSL line).
Back to FTTP: I have no idea if interleaving has been applied to the new FTTP line. - However, since there are supposed to be zero loses on a fibre
line with properly made fibre joints I cannot see why it should be unless there was an equipment problem.
It is either a line problem. an equipment problem or a contention problem.
The theory is that the line either works or it does not but it would be nice to test the quality of the optics to rule out any possibility of fibre line issues cause by dirty equipment etc..
Since it does vary irrespective of the time of day and night and I do not consistently get a full speed at 4:00AM in the morning contention is a far less likely culprit, (coupled with the fact that I am with Zen who usually have very low contention), but contention cannot be ruled out at this stage.
If contention is the problem then I am glad that I am with Zen and not someone else as I am confident that Zen will sort out any contention issues. - I hope that my faith in them is not misplaced but on the whole Zen have been an excellent ISP.
I do not know if it is an equipment problem or not; perhaps, there is an issue with my ONT or with the equipment at the local exchange.