Experience with a long line

I've been on fibre (FTTC) for nearly a year, but I am quite distant from Cabinet 70 (Cheltenham) - some 1000 metres.. Obviously this makes me far more vulnerable to deficiencies in the line and equipment. In fact I get an adequate and stable service at around 15 Mbps. But I feel that I ought to achieve nearer to 25Mbps.

My stats are:

VDSL Port Details Upstream Downstream
Attainable Net Data Rate: 1245 kbps 15868 kbps
Actual Aggregate Tx Power: 2.2 dBm 8.0 dBm
====================================================================================
VDSL Band Status U0 U1 U2 U3 U4 D1 D2 D3
Line Attenuation(dB): 11.2 69.4 N/A N/A N/A 25.7 84.9 N/A
Signal Attenuation(dB): 11.2 67.9 N/A N/A N/A 32.1 N/A N/A
SNR Margin(dB): 9.5 9.5 N/A N/A N/A 6.8 N/A N/A
TX Power(dBm): 0.1 -2.5 N/A N/A N/A 8.0 N/A N/A

I notice two points - which I assume are unconnected. First, the downstream power is rather low at 8.0, when figures above 12 dBm seem common and will obviously help the SNR. Second, the Signal Attenuation in band D1 is 6.4 dB higher than the Line Attenuation.

I'd welcome comments on this. Is there anything I can do to improve matters?

Is your modem unlocked with the latest firmware, or the earlier one?

As it reports U4 in pbParams, it looks like the latest version to me.

I'm roughly 1100m from the cabinet & these are my stats:-

Text

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xdslcmd info --pbParams xdslcmd: ADSL driver and PHY statusStatus: Showtime Retrain Reason: 1Last initialization procedure status:   0 Max:    Upstream rate = 4153 Kbps, Downstream rate = 21592 KbpsBearer: 0, Upstream rate = 4124 Kbps, Downstream rate = 21307 Kbps  Discovery Phase (Initial) Band Plan US: (7,32) (871,1205) (1972,2782) DS: (33,859) (1216,1961) (2793,3970) Medley Phase (Final) Band PlanUS: (7,32) (871,1196) DS: (33,859) (1216,1662)           VDSL Port Details               Upstream                Downstream Attainable Net Data Rate:            4153 kbps              21592 kbpsActual Aggregate Tx Power:             7.0 dBm               12.4 dBm ====================================================================================  VDSL Band Status       U0      U1      U2      U3      U4      D1      D2      D3   Line Attenuation(dB):  8.3     55.5     N/A     N/A     N/A    22.1    68.2     N/A   Signal Attenuation(dB):  8.3     54.6     N/A     N/A     N/A    31.3    68.1     N/A           SNR Margin(dB):  6.2     6.2      N/A     N/A     N/A    6.4     6.4      N/A            TX Power(dBm):  0.8     5.8      N/A     N/A     N/A    11.3    5.8      N/A .

From the Discovery Phase band plans it can be seen that I'm connected to a Huawei DSLAM.

I have lost around 10Mbps DS sync speed over 18 months or so, probably due to crosstalk.

I also have quite a difference between the D1 band's Line & Signal attenuation & it can be seen that I can't use all the available tones at Medley stage.


Some of that might be simply due to line length & some of it may be due to crosstalk.

Unfortunately, the updated firmware hadn't been released when I first started to see the effects of crosstalk & the older version didn't report the stats 'properly', so I was unable to see if D1 Signal attenuation actually deteriorated at that time.

e.g. D1 Line & Signal attenuation always had identical values as did Discovery & Medley phase band plans where any of the relevant band could be used.


I believe the updated firmware gives us a truer picture of connection stats than the original version.

Thanks for your reply with interesting stats for a similar line length that I can compare with mine. As you say, you have a similar difference between line attenuation and signal attenuation. But I also see that you have much more TX power - 4.4 dB more downstream, and 4.8dB more upstream. That's probably why you are getting faster speeds down and up. Do you know if I have any control over the upstream TX power ? - through xdslcmd ?

These are my stats, I am about 1000m from my cab. Though like you think I could get better but I think its most likely due to interleaving in my case not so much crosstalk actually as my speed will never get above 25mbps now used to get 26.5mbps but as other people such as my neighbors bought it that's all I can get now but not as bad as what others get through crosstalk and despite my cabinet's capacity filling up twice.
# xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY status
Status: Showtime
Retrain Reason: 0
Last initialization procedure status: 0
Max: Upstream rate = 5295 Kbps, Downstream rate = 26356 Kbps
Bearer: 0, Upstream rate = 2000 Kbps, Downstream rate = 25818 Kbps

Discovery Phase (Initial) Band Plan
US: (6,31) (882,1193) (1984,2770)
DS: (33,857) (1218,1959) (2795,4083)
Medley Phase (Final) Band Plan
US: (6,31) (882,1193)
DS: (41,857) (1218,1959)
VDSL Port Details Upstream Downst
ream
Attainable Net Data Rate: 5295 kbps 26356 kbps
Actual Aggregate Tx Power: 6.1 dBm 11.7 dBm
================================================================================
====
VDSL Band Status U0 U1 U2
U3 U4 D1 D2 D3
Line Attenuation(dB): 5.0 54.1 64.0 N/A N/A 21.9 68.3
N/A
Signal Attenuation(dB): 5.0 53.9 N/A N/A N/A 30.7 68.1
N/A
SNR Margin(dB): 13.2 12.8 N/A N/A N/A 4.3
4.3 N/A
TX Power(dBm): -3.9 5.6 N/A N/A N/A 10.3
6.1 N/A

In reply to a post by oaksider:

Thanks for your reply with interesting stats for a similar line length that I can compare with mine. As you say, you have a similar difference between line attenuation and signal attenuation. But I also see that you have much more TX power - 4.4 dB more downstream, and 4.8dB more upstream. That's probably why you are getting faster speeds down and up. Do you know if I have any control over the upstream TX power ? - through xdslcmd ?

I don't believe we users have any scope to increase TX Power.


Your TX Power may be lower than mine due to intentional cutting back on power at the cabinet (known as a PSD Power Mask or similar term) to avoid your connection swamping other weak connections in the area, probably ADSL connections.

If you actually graph your connection stats, I would 'guess' that quite a pronounced 'V' shape will be seen in the Bitloading & SNR graphs, indicating either where thesre is 'interference' or where your TX Power has been restricted.

Yes, you guess right. But it's more than just a 'V' shape. I can see that 'V' shape in several of other people's mydslstats graphs online.

But I have a whole block of tones entirely missing (from --Bits). There's good loading up to tone 369. Then there's a sudden complete gap from 370 to 515. Then tones return from 516 to 853, with loading trailing off. Then a few tones above 895 . --SNR is similar, tones from 370 to 515 having 0.0000, with just one or two exceptions at the bottom end.

Mysterious. Certainly looks like deliberate restriction between about 1.5 and 2.2 MHz. Nothing I can do, but it's nice to be getting a glimmering of understanding.