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[burakkucat]

I wonder if the more analytical of our members would be able to interpret the following statistics, harvested from a ZyXEL VMG1312-B10A that is acting as the CPE on a long metallic pathway, and is configured to operate only in ADSL2 (ITU-T G.992.3) mode. In particular, do the error counts hint at any possible problem? 

 > xdslctl info --show
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    8000
Last initialization procedure status:   0
Max:    Upstream rate = 417 Kbps, Downstream rate = 3428 Kbps
Bearer: 0, Upstream rate = 445 Kbps, Downstream rate = 3082 Kbps

Link Power State:       L0
Mode:                   ADSL2 Annex A
TPS-TC:                 ATM Mode(0x0)
Trellis:                U:ON /D:ON
Line Status:            No Defect
Training Status:        Showtime
                Down            Up
SNR (dB):        3.1             5.8
Attn(dB):        64.0            40.3
Pwr(dBm):        18.2            12.4

                        ADSL2 framing
                        Bearer 0
MSGc:           52              14
B:              35              46
M:              4               1
T:              3               1
R:              12              12
S:              1.4717          3.3007
L:              848             143
D:              2               8

                        Counters
                        Bearer 0
SF:             64333918                789747
SFErr:          1539            42
RS:             2798525458              999616
RSCorr:         84573           8888395
RSUnCorr:       3343            0

ReXmt:          54454           0
ReXmtCorr:      51851           0
ReXmtUnCorr:    3462            0

                        Bearer 0
HEC:            3953            39
OCD:            9               0
LCD:            9               0
Total Cells:    3238169092              1089949025
Data Cells:     360612088               43423312
Drop Cells:     0
Bit Errors:     188262          3954

ES:             227             40
SES:            9               0
UAS:            180             180
AS:             1036442

                        Bearer 0
INP:            26.00           2.50
INPRein:        0.00            0.00
delay:          8               7
PER:            16.00           16.50
OR:             28.99           9.69
AgR:            3097.23 453.88

Bitswap:        259493/261876           38946/38946

[boozy]

Hi B*Cat

1st Question - how long is the uptime?

You look as if you are having error bursts with 4% of Errored Seconds being SES... so I'm betting the problem is short lived and repetitive - have you got a ES graph?

I'm having experiments with two lines one of which has an SNR of 3 and the other of 11.  There's a surprisingly similar pattern on both lines despite the SNR difference. Your interference may be similar if the uptime is low (and have the same low chance of sussing it out if it is similar ).

[j0hn]

Is that your line B*cat?
The presence of PhyR caught my eye.

[burakkucat]

Thank you, both, for your comments. 

No, those harvested statistics do not relate to my circuit . . . but were "pushed under the door of The Cattery" early yesterday morning, with a note asking about the error counts. The only comment I could make was that without details of the relevant time-frame, etc, not a lot could be deduced.

[RealAleMadrid]

The AS figure (Available seconds) indicates an up time of almost exactly 12 days. 

[ejs]

So the error counts are basically not much. Is this one of Weaver's lines?

[j0hn]

The AS is only the time from the last resync but the accompanying ES/SES numbers are the total uptime.

Either way for at least 12 days (11.995 days) those numbers look great.
Even better if the modem uptime was longer than that.

[burakkucat]

. . . Is this one of Weaver's lines?

b*cat smiles, enigmatically. 

[Weaver]

Could someone be kind enough to talk me through the PhyR stats in this? To help me understand them?

[Alex Atkin UK]

I'm wondering what is the relevance of it being limited to ADSL2 vs ADSL2+?

I know on my 3-5Mbit line I was always surprised that ADSL2+ performed better when everything online at the time suggested it should have zero benefit on long lines.

[Weaver]

When I did that I had got the idea from a suggestion by Burakkucat. He thought that forcing a restriction to ADSL2 on a very long line may close the modem to shut its ears to the very high tones used by ADSL2+, thus narrowing the window and letting less noise in. I don’t know whether or not modems do this; it could be that they have the same input subsystem and there is a variable width input filter or the hardware could be identical. I assumed that it couldn’t hurt and so I tried the idea when I first went up to ADSL2 from G.992.1. Indeed the highest tones I can use are way too low for me to lose out on anything by using ADSL2 not ADSL2 A+.

[Alex Atkin UK]

Its been a long long time, but I seem to recall I lost some upstream speed if I limited to ADSL2.

But then with it being so long ago, the crosstalk situation is likely VERY different today.  The chances of getting those higher frequencies is probably much slimmer than when I last had it.

[Weaver]

Alex, did you mean to write “if I limited to ADSL2” ?

[Alex Atkin UK]

Alex, did you mean to write “if I limited to ADSL2” ?

Why yes, I did.

But thinking back, this was probably when I was on Be Broadband, so could also be why it made a difference back then.

[Weaver]

One difference which I noticed last night, is that if you have PhyR / G.998.4 / G.INP, for ADSL2 there are differences in the standards compared with ADSL2+ (and VDSL2). See G.998.4 annex A.

For ADSL2, the maximum amount of RAM to be allocated for the ReTX Tx queue in the DSLAM, quoting - "transmit retransmission queue in the CO" - is limited to the half of the downstream interleaver delay in bytes, i.e.: Q_tx* Q * H ≤ 8001 bytes". For ADSL2+ this figure can optionally be 12000 bytes instead - see annex B. The maximum value of Q*H is 1024 bytes, but I can’t see all the individual parameters for my modem.

So a constraint on performance is possibly relaxed with ADSL2+, by an implementation option. This will affect the range of patterns of lookback retransmission that can be supported, where a receiver can indicate a NACKed or ACKed DTU way back which is different from its successors. When such a circumstance could practically happen is quite unclear to me, and even the mere possibility is an option.

A more careful look might reveal other differences between ADSL2 and ADSL2+, but I have yet to do all the tedious work.