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Standard User StephenTodd
(committed) Mon 04-Feb-13 19:07:21
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Re: Plusnet FTTC unlimited


[re: WWWombat] [link to this post]
 
Thanks very much for that detail. I knew a little of it, but not most.
I do indeed have FEC on, as I have interleaving 1193 and delay 8.0; I monitor these fairly regularly.
I'll have a closer look at the others with interest when I've got a bit more time just to see how it all ties up.

I knew about the tcp window; but some downloads use a protocol like
request send 1MB
receive 1MB
request send 1MB
receive 1MB
etc
Each 1MB receive block gets the benefit of the tcp window to mask out latency,
but the latency comes in between complete receive of one block and the request of the next.

--
Moved (with trepidation) to BT Infinity 2 for upload speed. Happy BE user for several years.
Standard User StephenTodd
(committed) Tue 05-Feb-13 14:35:13
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Re: Plusnet FTTC unlimited


[re: WWWombat] [link to this post]
 
@WWWombat: Thanks again for that very informative post.

I've just had a look at my figures, shown complete below.
Clearly quite a few errors are causing quite high interleaving and FEC.
Still perfectly acceptable overall performance, though of course faster and less latency would be good.

One clarification on your post where my new understanding doesn't match my figures..
From what you said, I would have expected
Path = Max * (N-R)/N
as (N-R) is the number of useful bytes and N the total number.

However, for downstream, Rate = 75260 but Max * (N-R)/N = 70544,


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# xdslcmd info --show
xdslcmd: ADSL driver and PHY statusStatus: Showtime
Retrain Reason: 0Max:    Upstream rate = 23910 Kbps, Downstream rate = 88180 Kbps
Path:   0, Upstream rate = 20000 Kbps, Downstream rate = 75260 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):        6.0             15.4Attn(dB):        0.0             0.0
Pwr(dBm):        14.2            6.9                        VDSL2 framing
                        Path 0B:              63              237
M:              1               1T:              64              45
R:              16              16S:              0.0271          0.3782
L:              23651           5373D:              1193            1
I:              80              127N:              80              254
                        Counters                        Path 0
OHF:            3121191941              2325124OHFErr:         36655           633
RS:             2268398122              4210906RSCorr:         486883048               101183
RSUnCorr:       5403560         0 
                        Path 0HEC:            1977557         0
OCD:            0               0LCD:            0               0
Total Cells:    379436542               0Data Cells:     1303444197              0
Drop Cells:     0Bit Errors:     0               0
 ES:             1387            521
SES:            44              0UAS:            22              22
AS:             4069977 
                        Path 0INP:            3.00            0.00
PER:            1.29            4.25delay:          8.00            0.00
OR:             129.34          60.17 
Bitswap:        1622875         48270


--
Moved (with trepidation) to BT Infinity 2 for upload speed. Happy BE user for several years.
Standard User WWWombat
(fountain of knowledge) Tue 05-Feb-13 17:19:29
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Re: Plusnet FTTC unlimited


[re: StephenTodd] [link to this post]
 
In reply to a post by StephenTodd:
Clearly quite a few errors are causing quite high interleaving and FEC.

Wow!

If I read that correctly, about 25% of RS blocks are received with errors, but 99% of them get successfully corrected.

Your line is *definitely* in need of FEC and interleaving - it just wouldn't work otherwise!

One clarification on your post where my new understanding doesn't match my figures..
From what you said, I would have expected
Path = Max * (N-R)/N
as (N-R) is the number of useful bytes and N the total number.

However, for downstream, Rate = 75260 but Max * (N-R)/N = 70544,

In theory, that sounds about right.

Remember, though, that the "Max Attainable" alters based on current line conditions - particularly the current noise conditions - while the line speed and FEC/interleaving settings were all set in stone at the last sync (looks like 47 days ago). If it is noisier now than then, the "max attainable" figure will be lower.

What does your "--pbParams" output look like? If SNR is not 6dB, then line conditions have changed.

In practice, the Huawei also doesn't quite follow the theory. Whether it is a fault, or a consequence of the way it prepares the estimate, I don't know. When people swap between fastpath and FEC/interleaving, both line speed *and* max attainable change - usually in opposite directions.

The only thing we know for sure is that FEC is indeed eating capacity of your line - 16 bytes extra for each 64 bytes you receive


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Standard User StephenTodd
(committed) Tue 05-Feb-13 18:08:50
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Re: Plusnet FTTC unlimited


[re: WWWombat] [link to this post]
 
The line was running without interleaving for quite a time,
then suddenly got quite high interleaving (as you see) at a marginally increased sync rate.
Unfortunately, Windows Task Manager was being stroppy at the time so my statistics logging wasn't working.
It's still easily fast enough for my needs, and no gaming, so I hadn't really looked into the reason behind the interleaving.

The snr has been varying between 5 and 6 since the last connection.

Looking at the graphs I can see that there are a few bursts of very high RSCorr:.
I must look a bit deeper.
Thanks again.


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# xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY statusStatus: Showtime
Retrain Reason: 0Max:    Upstream rate = 24097 Kbps, Downstream rate = 86504 Kbps
Path:   0, Upstream rate = 20000 Kbps, Downstream rate = 75260 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:      24097 kbps         86504 kbps
Actual Aggregate Tx Power:        6.9 dBm          14.1 dBm============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3  Line Attenuation(dB):  4.6     24.5    37.3     N/A    12.2    30.1    47.2
Signal Attenuation(dB):  4.6     23.3    35.6     N/A    12.2    30.1    47.2        SNR Margin(dB):  15.5    15.5    15.5     N/A    6.6     5.0     4.9
         TX Power(dBm): -4.2    -19.3    6.4      N/A    10.6    8.0     7.3


--
Moved (with trepidation) to BT Infinity 2 for upload speed. Happy BE user for several years.
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