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Standard User D_an_W
(committed) Fri 05-Jul-13 18:14:32
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Do the --stats give clues to drop in speed?


[link to this post]
 
Hi folks, We got back off holiday recently and everything had been turned off for two weeks. Upon firing things back up I initially noticed a slight increase in Attainable rate and Line rate but the day after it had dropped to below the level it was at before we went away (The Attainable rate and Line rate are usually very close around 69500 each).

I have now tried a couple of "DRM friendly" resets leaving everything switched off either all day or overnight but I can't get the Line Rate to jump back up close to the Attainable rate as it used to be, can anyone with more talent than me take a peek at the stats below and see if there are any clues please?

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# xdslcmd info --stats
xdslcmd: ADSL driver and PHY statusStatus: Showtime
Retrain Reason: 0Max:    Upstream rate = 26658 Kbps, Downstream rate = 74164 Kbps
Path:   0, Upstream rate = 20000 Kbps, Downstream rate = 64204 Kbps 
Link Power State:       L0Mode:                   VDSL2 Annex B
VDSL2 Profile:          Profile 17aTPS-TC:                 PTM Mode
Trellis:                U:ON /D:ONLine Status:            No Defect
Training Status:        Showtime                Down            Up
SNR (dB):        6.1             15.1Attn(dB):        0.0             0.0
Pwr(dBm):        12.5            6.8                        VDSL2 framing
                        Path 0B:              51              237
M:              1               1T:              64              45
R:              12              16S:              0.0258          0.3782
L:              19868           5373D:              1257            1
I:              64              127N:              64              254
                        Counters                        Path 0
OHF:            357541          138949OHFErr:         0               0
RS:             91377317                1956294RSCorr:         1071            0
RSUnCorr:       0               0 
                        Path 0HEC:            0               0
OCD:            0               0LCD:            0               0
Total Cells:    73052240                0Data Cells:     308115          0
Drop Cells:     0Bit Errors:     0               0
 ES:             0               0
SES:            0               0UAS:            598             598
AS:             593 
                        Path 0INP:            3.00            0.00
PER:            1.64            4.25delay:          8.00            0.00
OR:             116.41          60.17 
Bitswap:        56              3 
Total time = 30 min 33 secFEC:            1071            0
CRC:            0               0ES:             0               0
SES:            0               0UAS:            598             598
LOS:            0               0LOF:            0               0
Latest 15 minutes time = 33 secFEC:            0               0
CRC:            0               0ES:             0               0
SES:            0               0UAS:            0               0
LOS:            0               0LOF:            0               0
Previous 15 minutes time = 15 min 0 secFEC:            1071            0
CRC:            0               0ES:             0               0
SES:            0               0UAS:            172             172
LOS:            0               0LOF:            0               0
Latest 1 day time = 30 min 33 secFEC:            1071            0
CRC:            0               0ES:             0               0
SES:            0               0UAS:            598             598
LOS:            0               0LOF:            0               0
Previous 1 day time = 0 secFEC:            0               0
CRC:            0               0ES:             0               0
SES:            0               0UAS:            0               0
LOS:            0               0LOF:            0               0
Since Link time = 9 min 51 secFEC:            1071            0
CRC:            0               0ES:             0               0
SES:            0               0UAS:            0               0
LOS:            0               0LOF:            0               0
Standard User XRaySpeX
(eat-sleep-adslguide) Fri 05-Jul-13 18:24:02
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Re: Do the --stats give clues to drop in speed?


[re: D_an_W] [link to this post]
 
Crosstalk? And it will only get worse as more join your cab.

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC
Standard User D_an_W
(committed) Fri 05-Jul-13 18:28:10
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Re: Do the --stats give clues to drop in speed?


[re: XRaySpeX] [link to this post]
 
Does that mean they managed to get the big chain and padlock off that I left around the cabinet to stop anyone else using it!!! wink

I did think of that but would that be more of a gradual thing especially as I initially saw an increase in speed?


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Standard User Bald_Eagle1
(experienced) Fri 05-Jul-13 19:15:07
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Re: Do the --stats give clues to drop in speed?


[re: D_an_W] [link to this post]
 
Maybe posting xdslcmd info --pbParams data would be useful, along with both sets of stats from when the connection had higher sync speed.

It does appear that just one additional connection to the cabinet can cause a drop of 5 Mbps or more in sync speeds.

Your Interleaving depth does seem quite high, so maybe your connection does suffer from some 'interference'.

DS SNR at 6.1 dB does suggest that the connection is currently maxing out whatever is available.

We have seen a couple of cases recently where DS power seems to have been reduced (thus lower sync speeds), particularly in the D2 band, possibly as a measure to avoid your own connection causing crosstalk issues on other connections.

The pbParams before & after data may confirm that has happened (or not).
Standard User D_an_W
(committed) Fri 05-Jul-13 19:24:04
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Re: Do the --stats give clues to drop in speed?


[re: Bald_Eagle1] [link to this post]
 
Thanks for the quick response folks!

I wish I had the stats for the higher sync speed but sadly not, I was busy after two weeks in Italy and enjoying the higher speed smile

Here is the current --pbParams data however if it helps?

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# xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY statusStatus: Showtime
Retrain Reason: 0Max:    Upstream rate = 26639 Kbps, Downstream rate = 73712 Kbps
Path:   0, Upstream rate = 20000 Kbps, Downstream rate = 64204 Kbps 
Discovery Phase (Initial) Band PlanUS: (0,95) (868,1207) (1972,2783) 
DS: (32,859) (1216,1963) (2792,3959) Medley Phase (Final) Band Plan
US: (0,95) (868,1207) (1972,2783) DS: (32,859) (1216,1963) (2792,3959) 
       VDSL Port Details       Upstream        DownstreamAttainable Net Data Rate:      26639 kbps         73712 kbps
Actual Aggregate Tx Power:        6.8 dBm          12.5 dBm============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3  Line Attenuation(dB):  4.0     20.1    29.9     N/A    10.7    25.3    38.0   
Signal Attenuation(dB):  4.0     19.2    29.0     N/A    10.7    25.3    38.0           SNR Margin(dB):  15.3    14.9    15.1     N/A    6.0     5.9     5.9    
         TX Power(dBm): -5.5    -24.0    6.5      N/A    8.4     7.8     7.0
Standard User Bald_Eagle1
(experienced) Fri 05-Jul-13 19:41:26
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Re: Do the --stats give clues to drop in speed?


[re: D_an_W] [link to this post]
 
Here's something from around 12 months ago for comparison.

I THINK it's from your own connection.

It was on fastpath back then.


Stats from 22/06/12
Standard User D_an_W
(committed) Fri 05-Jul-13 19:45:21
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Re: Do the --stats give clues to drop in speed?


[re: Bald_Eagle1] [link to this post]
 
Ohh...I forgot about those.

For the dumb one here (Me!), how do I tell if I am on Fastpath or Interleaved?

Here is one from just under 12 months ago which is pretty much how it has been ever since up until returning from holiday...

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# xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY statusStatus: Showtime
Retrain Reason: 0Max:    Upstream rate = 24844 Kbps, Downstream rate = 70976 Kbps
Path:   0, Upstream rate = 20000 Kbps, Downstream rate = 70070 Kbps 
Discovery Phase (Initial) Band PlanUS: (0,95) (868,1207) (1972,2783) 
DS: (32,859) (1216,1963) (2792,3959) Medley Phase (Final) Band Plan
US: (0,95) (868,1207) (1972,2783) DS: (32,859) (1216,1963) (2792,3959) 
       VDSL Port Details       Upstream        DownstreamAttainable Net Data Rate:      24844 kbps         70976 kbps
Actual Aggregate Tx Power:        6.8 dBm          12.6 dBm============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3  Line Attenuation(dB):  4.0     20.0    29.4     N/A    10.7    25.1    37.7   
Signal Attenuation(dB):  9.5     19.2    28.6     N/A    10.7    25.1    37.7           SNR Margin(dB):  15.0    14.9    15.0     N/A    6.2     6.2     6.2    
         TX Power(dBm): -5.3    -24.2    6.5      N/A    8.4     8.0     6.9    #


Could this be when it happened (I always forget about this tool too)...

My Broadband Ping

Edited by D_an_W (Fri 05-Jul-13 19:51:56)

Standard User WWWombat
(fountain of knowledge) Fri 05-Jul-13 20:05:01
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Re: Do the --stats give clues to drop in speed?


[re: D_an_W] [link to this post]
 
In reply to a post by D_an_W:
(The Attainable rate and Line rate are usually very close around 69500 each).

DLM has added FEC/interleaving. It has requested INP protection of 3.00 and allows a maximum delay of 8ms - these are the common values that DLM uses for a first attempt.

As a result, the FEC overhead has been set at 12 bytes out of every 64, which amounts to 19% - so your sync speed ends up that much below the attainable.

Presumably crosstalk has kicked in - but it doesn't do so in a linear, gradual fashion. It is all random, depending on which pair runs close to yours in the cable(s), and which subscribers take FTTC. The documentation on vectoring suggests that a line may suffer from a subset of 5-6 major disturbers from all the lines in the cable.

Even if the crosstalk you are experiencing *does* impact your line gradually, the decision to turn on FEC/interleaving happens when the error rate hits a threshold. Once you go over the threshold, then bam! ... immediate loss of 20% of sync speed. A definite case of "the straw that broke the camel's back".

Ironically...
Once FEC/interleaving has been turned on, the attainable speed seems to increase by about the same amount as the actual speed decreases. Your line has done the same.

I have now tried a couple of "DRM friendly" resets leaving everything switched off either all day or overnight but I can't get the Line Rate to jump back up close to the Attainable rate as it used to be

Won't happen.

DLM might turn off interleaving after 2-4 weeks, if the error rate has improved, though obviously it needs to be watching how FEC stats are performing to decide whether to downgrade the intervention.
Standard User D_an_W
(committed) Fri 05-Jul-13 20:13:44
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Re: Do the --stats give clues to drop in speed?


[re: WWWombat] [link to this post]
 
WOW!

Thanks so much folks, I couldn't have wished for a better response!

I assume this is all out of the ISP's hands (I am not with BT) and it's not something that could be switched off or reset?

I am pretty certain it is now at the speed it was at when I first moved to 80/20 but after a while it increased to the pre-holiday level and stayed there so I will leave the connection alone now for a few weeks in the hope it settles back down.
Standard User WWWombat
(fountain of knowledge) Fri 05-Jul-13 22:43:41
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Re: Do the --stats give clues to drop in speed?


[re: D_an_W] [link to this post]
 
In reply to a post by D_an_W:
For the dumb one here (Me!), how do I tell if I am on Fastpath or Interleaved?


Sorry - missed this.

There are 3 separate things to look for in the "--stats" info

a) If "INP" and "delay" are non-zero, then DLM has asked for intervention.
This may happen separately for upstream and downstream.

On your line, DLM wants intervention on the downstream, but not the upstream.

b) If "D" is higher than 1, then interleaving is turned on - and this usually only happens if "delay" is non-zero - and it is this that contributes to the added latency.

On your line, you have interleaving turned on for downstream, but not upstream.

c) If "R" is non-zero, then FEC is turned on. This will be on when interleaving is turned on, and causes extra "correction" data to be sent alongside your data. This extra data is hidden from you, and is what causes a reduction in sync speed.

However, FEC might also be turned on (without interleaving) even if DLM hasn't demanded it - usually when there is a lot of spare sync speed available. The modems seem to decide this on their own, as the overhead can be handled easily.

On your line, FEC is turned on for both upstream and downstream. In the downstream case, it steals some capacity from your sync speed. In the upstream, there is enough spare capacity for it to not be noticed: the overhead is (R/N), or 16 bytes out of every 254, or about 7%.
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