ISP: Now Broadband (Sky)
Product: 40/10 Openreach FTTC
Line length: Around 1km + 50m from PCP to FTTC cab
GEA Stability Profile: Standard (assumed)
FTTC DSLAM type: Huawei (BDCM:0xa4a1)
Routers: Now Hub 2 and Zyxel VMG3925-B10C (both Broadcom)
Local plant: NTE5C + Mk4 faceplate, external cable direct into back of NTE. One join (jelly crimps in BT16A) from drop cable to CW1308 cable which goes into NTE. RJ45 to RJ11 Cat5e cable from Mk4 faceplate to router.
Day 1: No speed band, 6db DS target, downstream retransmit low, upstream error protection off.
Upstream rate = 3943 Kbps, Downstream rate = 28257 Kbps
Day 2: No speed band, 6db DS target, downstream retransmit low, upstream error protection off.
Day 3: Resync at around 3am, no visible change to stats (reason 2: RDI detector).
Day 4: No change
Day 5: No change
Day 6: DLM resync at 6am: 6db DS target, downstream retransmit high, upstream error protection off.
Upstream rate = 3355 Kbps, Downstream rate = 26744 Kbps
Day 7: DLM resync at 2am: Downstream:
banded 25M, retransmit high, upstream:
banded 3.2M, error protection off.
Day 8: 3am: Downstream:
banded 22.5M, upstream:
banded 2.8M, error protection off.
Day 9: No change
Day 10: Downstream:
banded 20M, upstream:
banded 2.3M, error protection off.
Day 11: Downstream:
banded 18M, upstream:
banded 2M, error protection off.
On day 10: ISP line test failed with "Impairment in copper joint detected".
On day 11, Openreach Engineer attended:
- Line test from NTE showed HR joint fault.
- Line test at PCP back to my NTE: no fault.
- Line test at PCP on FTTC tie cables: battery contact and earth contact!
First new port allocation dropped sync after 2 mins.
Second set didn't sync in the PCP at all.
Third set requested on a different 'block', synced at 40/10 following a DLM reset.
No other changes made to line, same D-side, just different FTTC port and tie cables from PCP to FTTC cab (around 50m).
VDSL2 link up, Bearer 0, us=5075, ds=28077VDSL2 link up, Bearer 1, us=0, ds=0
So appears to be back to unbanded, DS retx low, US error protection off (assumed, as back to where we started on da 1). No detailed stats as using ISP supplied router (Now Hub 2). I will update this thread with the timeline now that the line has been fixed.
Observations:
- Despite being on retransmit low, speedtests seem limited to between around 89% and 92% of sync rate. Potentially some kind of shaping that Sky are doing on their BNG, but 92.6% is the best I've had, straight after the FTTC port swap and DLM reset. This is wired, with only one device connected to the router.
- DLM seemed to be intervening quite heavily, even when CRC/ES were low. I'll try and dig out the G.INP stats to check LEFTRS and tx_uc counters.
- Upstream and downstream both seemed to be banded at the same time, and were stepped down together. Given the nature of the fault though, it's likely they were both bad enough to need intervention!
- This line has been used on and off in the last 6 years, and I suspect has always had some issues which have never been solved, as it's only been used as a backup/test line until now, so never been worth the effort. The 5Mb upstream sync straight after the fault fix is the highest I've ever seen.
- Knowing the issues with this line, I was anxious about using an ISP that uses the Standard stability profile, and not Speed. In retrospect, it looks like the more stability-focussed Standard profile helped me out here, as it managed to get the line to a low enough speed for the ISP to take the issue seriously. Of course, the failing line test also helped with that.
- FTTC cabinet is around 3km from the exchange, so I expect some upstream power backoff is applied.
Day 1 stats:
ZySH> xdslctl info --stats
Max: Upstream rate = 3947 Kbps, Downstream rate = 29212 Kbps
Bearer: 0, Upstream rate = 3943 Kbps, Downstream rate = 28257 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Down Up
SNR (dB): 6.8 6.2
Attn(dB): 30.3 0.0
Pwr(dBm): 11.3 6.9
Bearer 0
INP: 43.00 0.00
INPRein: 0.00 0.00
delay: 0 0
PER: 0.00 9.02
OR: 0.01 28.36
AgR: 28285.72 3971.68
Bearer 1
INP: 2.50 0.00
INPRein: 2.50 0.00
delay: 0 0
PER: 16.06 0.01
OR: 47.81 0.01
AgR: 47.81 0.01Day 2 stats:
ZySH> xdslctl info --stats
xdslctl: ADSL driver and PHY status
Max: Upstream rate = 3455 Kbps, Downstream rate = 29285 Kbps
Bearer: 0, Upstream rate = 3455 Kbps, Downstream rate = 27881 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Down Up
SNR (dB): 6.8 6.3
Attn(dB): 30.3 0.0
Pwr(dBm): 11.3 6.9
Bearer 0
INP: 43.00 0.00
INPRein: 0.00 0.00
delay: 0 0
PER: 0.00 9.04
OR: 0.01 28.31
AgR: 27925.43 3483.00
Bearer 1
INP: 2.50 0.00
INPRein: 2.50 0.00
delay: 0 0
PER: 16.06 0.01
OR: 47.81 0.01
AgR: 47.81 0.01
Day 6 stats:
ZySH> xdslctl info --stats
Max: Upstream rate = 3239 Kbps, Downstream rate = 27038 Kbps
Bearer: 0, Upstream rate = 3355 Kbps, Downstream rate = 26744 Kbps
Bearer: 1, Upstream rate = 0 Kbps, Downstream rate = 0 Kbps
Down Up
SNR (dB): 6.4 4.6
Attn(dB): 30.7 0.0
Pwr(dBm): 11.3 6.9
Bearer 0
INP: 55.00 0.00
INPRein: 1.00 0.00
delay: 0 0
PER: 0.00 9.07
OR: 0.01 28.19
AgR: 26803.10 3383.70
Bearer 1
INP: 2.50 0.00
INPRein: 2.50 0.00
delay: 0 0
PER: 16.06 0.01
OR: 47.81 0.01
AgR: 47.81 0.01
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Topic: DLM behaviour on new FTTC installation (1km line) (Read 2929 times)