In the early days of Zen's backhaul network they were mistakenly ordering 'own network' FTTC ports on a more conservative (lower speed, potentially higher stability) than they chose for WBMC FTTC ports. On WBMC, Zen chose the most speed orientated profile by default. I believe part of the reason for this is that Openreach confusingly use different names for the three profiles than BT Wholesale do.
This problem was resolved long ago; Zen now order 'own network' FTTC ports and WBMC FTTC ports on the most speed orientated profile by default. Accordingly, this is not your issue.
If you post your statistics, we might be able to advise further. However, the loss of 5Mbit/s download speed is not unusual when work on a line takes place; the PCP work may well have lead to increased crosstalk. Crosstalk would also explain a drop in available speed; I'm not clear whether you're talking about available speed or sync speed.
I am talking about a drop it max attainable speed from 85Mbps ( which it has held steady for over 2 years) and the 78Mbps now. In 'real' terms, I accept that I have no reason to be unhappy. My status are as follows:
Receive Direction Send Direction
Max. DSLAM throughput kbit/s 80000 20000
Min. DSLAM throughput kbit/s 128 128
Attainable throughput kbit/s 77961 25727
Current throughput kbit/s 77961 20000
Seamless rate adaptation off off
Latency fast fast
Impulse Noise Protection (INP) 0 0
G.INP off off
Signal-to-noise ratio dB 5 9
Bitswap on on
Line attenuation dB 13 12
G.Vector off off
Carrier record A43 A43
Seconds With Not Remediable Errors (CRC)
Errors (ES) Many
Errors (SES) per
FRITZ!Box 687 0 0.13 7
Central exchange 36 0 0 0
When my line was changed to GEA 5 days ago, the downstream SNR was a steady 6. It is now down to 5 with periods as low as 4. A fall in SNR does not generate extra errors. My line is via an ECI cabinet.
Edited by lexden16 (Mon 20-Mar-17 12:36:56)