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Standard User Matt182
(member) Thu 21-Feb-13 21:28:22
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Max Attainable differs from Actual line rate


[link to this post]
 
For a few months I have noticed the max attainable rate reported by the FTTC modem declining below the actual line rate and was wondering if anyone else had noticed this?

Right now the max attainable is at 70,664kbit/s and my line rate is 79,999kbit/s just thought it was a bit odd and was not sure if its a bug in the reporting.

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# xdslcmd info --pbParams
xdslcmd: ADSL driver and PHY statusStatus: Showtime
Retrain Reason: 2Max:    Upstream rate = 27370 Kbps, Downstream rate = 70664 Kbps
Path:   0, Upstream rate = 20000 Kbps, Downstream rate = 79999 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:      27370 kbps         70664 kbps
Actual Aggregate Tx Power:        6.0 dBm          13.3 dBm============================================================================
  VDSL Band Status        U0      U1      U2      U3      D1      D2      D3  Line Attenuation(dB):  3.3     17.2    25.0     N/A    9.5     21.6    34.0
 Signal Attenuation(dB):  3.3     16.1    23.6     N/A    9.5     21.6    34.0
         SNR Margin(dB):  11.6    12.0    11.9     N/A    3.4     3.4     3.4
          TX Power(dBm): -8.8    -28.1    5.9      N/A    10.2    7.8     7.0


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# xdslcmd info --show
xdslcmd: ADSL driver and PHY statusStatus: Showtime
Retrain Reason: 2Max:    Upstream rate = 27394 Kbps, Downstream rate = 70664 Kbps
Path:   0, Upstream rate = 20000 Kbps, Downstream rate = 79999 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):        3.4             12.0Attn(dB):        0.0             0.0
Pwr(dBm):        13.3            6.0                        VDSL2 framing
                        Path 0B:              239             237
M:              1               1T:              23              45
R:              0               16S:              0.0955          0.3782
L:              20107           5373D:              1               1
I:              240             127N:              240             254
                        Counters                        Path 0
OHF:            1968359053              3943889OHFErr:         44244           5884
RS:             0               4291995RSCorr:         0               205170
RSUnCorr:       0               0 
                        Path 0HEC:            87307           0
OCD:            0               0LCD:            0               0
Total Cells:    3534465012              0Data Cells:     3583340644              0
Drop Cells:     0Bit Errors:     0               0
 ES:             37420           7141
SES:            13              88UAS:            274             274
AS:             10357172 
                        Path 0INP:            0.00            0.00
PER:            1.64            4.25delay:          0.00            0.00
OR:             116.56          60.17 
Bitswap:        1746117         195137


-------------------------------------------------------------
# TISCALI -> freeserve -> Wanadoo -> plusnet -> ZeN -> ADSL24 -> ZeN -> Sky -> BTInfinity Option 2

BT FTTC
http://www.speedtest.net/result/2033788623.png
Standard User RobertoS
(sensei) Thu 21-Feb-13 21:42:45
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Re: Max Attainable differs from Actual line rate


[re: Matt182] [link to this post]
 
I'd say a fair bit of noise is now present on the line, but not enough to cause your modem to lose sync and reconnect. The normal noise margin is around 6dB and yours is way down from that.

Don't touch it! I'd be fairly sure the next time the modem connects it will be around that "Max" figure. Unless you have something that may be chucking noise onto the line. In which case turn off whatever it is and see what happens to the stats.

My broadband basic info/help site - www.robertos.me.uk | Domains,website and mail hosting - Tsohost.
Connection - Plusnet UnLim Fibre (FTTC). Sync ~ 541/15.2Mbps @ 600m. - BQM

"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.
Standard User MHC
(sensei) Thu 21-Feb-13 21:49:05
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Re: Max Attainable differs from Actual line rate


[re: Matt182] [link to this post]
 
I see the same on a regular basis. Even after a resync the Max Attainable has been lower than actual.

If there is too much noise and your sync cannot be achieved you will just see a large increase in errors.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit


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Standard User RobertoS
(sensei) Thu 21-Feb-13 22:01:33
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Re: Max Attainable differs from Actual line rate


[re: MHC] [link to this post]
 
More than 9Mbps?

My broadband basic info/help site - www.robertos.me.uk | Domains,website and mail hosting - Tsohost.
Connection - Plusnet UnLim Fibre (FTTC). Sync ~ 541/15.2Mbps @ 600m. - BQM

"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.
Standard User MHC
(sensei) Thu 21-Feb-13 22:07:39
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Re: Max Attainable differs from Actual line rate


[re: RobertoS] [link to this post]
 
About 57 Attainable and a 63 sync ... so in of the same order


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User jchamier
(knowledge is power) Thu 21-Feb-13 22:10:56
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Re: Max Attainable differs from Actual line rate


[re: RobertoS] [link to this post]
 
In reply to a post by RobertoS:
More than 9Mbps?


I get the opposite, which I guess is more usual?

Max: Upstream rate = 9090 Kbps, Downstream rate = 55152 Kbps
Path: 0, Upstream rate = 10497 Kbps, Downstream rate = 48945 Kbps

James BT Infinity 2 19/09/2012 - Estimate 44.6/6.5 - Install 52/12 - Actual 46 / 8 Mbps
Huawei VDSL -> Draytek router -> Apple Airport Extreme -> Belkin Switch -> Windows/Mac/Linux/NAS/Phone
13 years of broadband - 1999 ntl:(512k/1M)/BTbusiness(2M)/Metronet(2M)/Bulldog(8M/16M)/BE(19M/16M)/BT FTTC(46M)

Edited by jchamier (Thu 21-Feb-13 22:11:28)

Standard User Ignitionnet
(knowledge is power) Thu 21-Feb-13 23:21:43
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Re: Max Attainable differs from Actual line rate


[re: Matt182] [link to this post]
 
In reply to a post by Matt182:
VDSL Band Status U0 U1 U2 U3 D1 D2 D3
Line Attenuation(dB): 3.3 17.2 25.0 N/A 9.5 21.6 34.0

Signal Attenuation(dB): 3.3 16.1 23.6 N/A 9.5 21.6 34.0

SNR Margin(dB): 11.6 12.0 11.9 N/A 3.4 3.4 3.4

TX Power(dBm): -8.8 -28.1 5.9 N/A 10.2 7.8 7.0

Max: Upstream rate = 27394 Kbps, Downstream rate = 70664 Kbps
Path: 0, Upstream rate = 20000 Kbps, Downstream rate = 79999 Kbps


Down Up
SNR (dB): 3.4 12.0
Attn(dB): 0.0 0.0
Pwr(dBm): 13.3 6.0


The bits in bold tell the story.
Standard User Matt182
(member) Fri 22-Feb-13 00:06:32
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Re: Max Attainable differs from Actual line rate


[re: RobertoS] [link to this post]
 
Thanks lads for the replies.

So I take it if the noise margin drops any more my connection will be at risk or dropping and resyncing at a lower speed. Funny thing is only the other day I checked and it was at 5.3dB so I wonder if this is the effects of crosstalk starting to take hold because itís slowly been reducing from 85Mbps @ 13.2dB since I moved over to the 80/20 package back in April.

Will keep an eye on it anyway and if I resync at a lower speed I will update this thread, hoping this will not happen though.

-------------------------------------------------------------
# TISCALI -> freeserve -> Wanadoo -> plusnet -> ZeN -> ADSL24 -> ZeN -> Sky -> BTInfinity Option 2

BT FTTC
http://www.speedtest.net/result/2033788623.png
Standard User Chrysalis
(eat-sleep-adslguide) Fri 22-Feb-13 00:49:40
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Re: Max Attainable differs from Actual line rate


[re: Matt182] [link to this post]
 
you already at risk, but if you want to keep that speed do not reboot it.

How common this occurs ultimately depends on how stable the line is.

Someone with a very stable line will probably not often if at all see an attainable below their current sync and they extremely unlikely to see it if they have excess snrm.

Quite simply your target snrm is 6db (or I assume it is) but the current snrm is below that hence the lower attainable. Probably increased crosstalk since it last synced. But the noise luckily for you isnt enough to make the modem drop yet.

BT Infinity 2 Since Dec 2012 - Estimate 65.9/20 - Attainable peak 110/36 - Current Sync 71/20
Standard User Bald_Eagle1
(committed) Fri 22-Feb-13 08:50:20
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Re: Max Attainable differs from Actual line rate


[re: Matt182] [link to this post]
 
The HG612 seems to be very good at hanging on to a connection at very low SNRM levels.

On my own connection (before the external cabling was repaired/partially replaced), I did occasionally see SNRM at negative values yet the connection didn't resync.

Looking at stats for other users' connections I have seen levels of 1.5dB at a 'noisy' time & back to around 6dB as conditions 'quietened' - again without a resync.

If you can, check the SNRM levels around noon to 2pm. That is 'usually' the quietest period.

Attainable rates increase/decrease in line with increases/decreases in SNRM levels.

Edited by Bald_Eagle1 (Fri 22-Feb-13 08:51:09)

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