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Author Topic: HEC errors, non-reporting and PTM vs ATM on ADSL2  (Read 3793 times)

Weaver

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HEC errors, non-reporting and PTM vs ATM on ADSL2
« on: October 06, 2016, 04:04:21 PM »

When modems report "HEC errors" I wonder if they are counting (i) detected errors, or (ii) number of cells with at least one detected error, or (iii) uncorrectable errors? If it's not the latter then you don't have to really worry, it's just potential trouble ahead. It would be interesting to know what the three individual counts are.
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Weaver

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #1 on: October 06, 2016, 04:05:30 PM »

One other thing: For some reason, I'm not seeing downstream HEC counts any more, AA just report "N/A". This started when I went 21CN. Don't suppose there is any chance I'm using PTM instead of ATM now I'm on ADSL2 ? Can't remember what we said about the availability of PTM when we were discussing it earlier.

Does anyone else who is on ADSL2/2+ see no reporting of HEC errors? Or any indication they might be using PTM?
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Weaver

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #2 on: October 06, 2016, 04:32:35 PM »

I remember now, ejs thought no-one actually uses PTM in G.992.3 (ADSL2) -
    http://forum.kitz.co.uk/index.php/topic,18489.msg333398.html#msg333398
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burakkucat

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #3 on: October 06, 2016, 05:18:23 PM »

As you will recall, my service is configured as G.992.5 from the TalkTalk (exchange based) MSAN and due to the length of the line (& thus the circuit's attenuation) I have configured my modem/router (a ZyXEL VMG1312-B10D) to G.992.3 mode.

(Observation: I note that the modem/router will allow me to configure the usage of either ATM or PTM for G.992.{1|3|5} mode. Whether I would be able to establish a viable link, I do not know . . . for I have not tried it.)

Here follows the output of the "xdslctl info", the "xdslctl info --state", the "xdslctl info --show" and the "xdslctl info --stats" command lines --

Code: [Select]
ZyXEL login: admin
Password:


BusyBox v1.20.1 (2016-06-06 11:34:28 CST) built-in shell (ash)
Enter 'help' for a list of built-in commands.

$ xdslctl info
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    8000
Last initialization procedure status:   0
Max:    Upstream rate = 1028 Kbps, Downstream rate = 5732 Kbps
Bearer: 0, Upstream rate = 1011 Kbps, Downstream rate = 5448 Kbps

$ xdslctl info --state
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    8000
Last initialization procedure status:   0
Max:    Upstream rate = 1020 Kbps, Downstream rate = 5772 Kbps
Bearer: 0, Upstream rate = 1011 Kbps, Downstream rate = 5448 Kbps

$ xdslctl info --show
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    8000
Last initialization procedure status:   0
Max:    Upstream rate = 1032 Kbps, Downstream rate = 5776 Kbps
Bearer: 0, Upstream rate = 1011 Kbps, Downstream rate = 5448 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):        6.2             6.1
Attn(dB):        46.0            28.9
Pwr(dBm):        0.0             12.8

                        ADSL2 framing
                        Bearer 0
MSGc:           61              10
B:              165             46
M:              1               4
T:              1               3
R:              6               4
S:              0.9690          5.9077
L:              1420            260
D:              64              4

                        Counters
                        Bearer 0
SF:             856235          784262
SFErr:          353             28
RS:             57367668                819831
RSCorr:         31583           58
RSUnCorr:       6215            0

                        Bearer 0
HEC:            3091            18
OCD:            0               0
LCD:            0               0
Total Cells:    178597862               33037026
Data Cells:     4058805         381229
Drop Cells:     0
Bit Errors:     338322          2823

ES:             140             21
SES:            0               0
UAS:            51              51
AS:             13896

                        Bearer 0
INP:            1.00            0.00
INPRein:        0.00            0.00
delay:          16              6
PER:            16.23           17.72
OR:             33.02           7.22
AgR:            5460.53 1014.37

Bitswap:        184/184         16/16

$ xdslctl info --stats
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    8000
Last initialization procedure status:   0
Max:    Upstream rate = 1032 Kbps, Downstream rate = 5772 Kbps
Bearer: 0, Upstream rate = 1011 Kbps, Downstream rate = 5448 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):        6.1             6.1
Attn(dB):        46.0            28.9
Pwr(dBm):        0.0             12.8

                        ADSL2 framing
                        Bearer 0
MSGc:           61              10
B:              165             46
M:              1               4
T:              1               3
R:              6               4
S:              0.9690          5.9077
L:              1420            260
D:              64              4

                        Counters
                        Bearer 0
SF:             856977          784941
SFErr:          353             28
RS:             57417352                827980
RSCorr:         31583           58
RSUnCorr:       6215            0

                        Bearer 0
HEC:            3091            18
OCD:            0               0
LCD:            0               0
Total Cells:    178752538               33065688
Data Cells:     4058808         381235
Drop Cells:     0
Bit Errors:     338322          2823

ES:             140             21
SES:            0               0
UAS:            51              51
AS:             13907

                        Bearer 0
INP:            1.00            0.00
INPRein:        0.00            0.00
delay:          16              6
PER:            16.23           17.72
OR:             33.02           7.22
AgR:            5460.53 1014.37

Bitswap:        184/184         16/16

Total time = 3 hours 52 min 42 sec
FEC:            31583           58
CRC:            353             28
ES:             140             21
SES:            0               0
UAS:            51              51
LOS:            0               0
LOF:            0               0
LOM:            0               0
Retr:           0
Latest 15 minutes time = 7 min 42 sec
FEC:            241             0
CRC:            2               0
ES:             1               0
SES:            0               0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            0               0
Retr:           0
Previous 15 minutes time = 15 min 0 sec
FEC:            233             0
CRC:            2               0
ES:             2               0
SES:            0               0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            0               0
Retr:           N/A
Latest 1 day time = 3 hours 52 min 42 sec
FEC:            31583           58
CRC:            353             28
ES:             140             21
SES:            0               0
UAS:            51              51
LOS:            0               0
LOF:            0               0
LOM:            0               0
Retr:           0
Previous 1 day time = 0 sec
FEC:            0               0
CRC:            0               0
ES:             0               0
SES:            0               0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            0               0
Retr:           0
Since Link time = 3 hours 51 min 51 sec
FEC:            31583           58
CRC:            353             28
ES:             140             21
SES:            0               0
UAS:            0               0
LOS:            0               0
LOF:            0               0
LOM:            0               0
Retr:           0
NTR: mipsCntAtNtr=0 ncoCntAtNtr=0
$

Note that HECs are reported by the "--show" and "--stats" variants of the "xdslctl info" command line.
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Weaver

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #4 on: October 06, 2016, 06:28:41 PM »

Extremely useful, many thanks. These figures have typically (and understandably) terse labels. I wonder if anything can be deduced from their values as to what their precise meaning is. I noticed that RS-related event counters are broken down in more helpful detail.

The PTM experiment would be very interesting.
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ejs

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #5 on: October 06, 2016, 06:59:36 PM »

I think HEC errors should be reporting the number of cells with one or more errors, I'm not sure if it can detect the exact number of bit errors in the cell header. All HEC errors are uncorrected. ATM HEC in general is able to correct single bit errors in the cell header, but the error correction is not used on DSL - refer to G.992.3 K.2.8.5.
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burakkucat

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #6 on: October 06, 2016, 09:03:52 PM »

These figures have typically (and understandably) terse labels. I wonder if anything can be deduced from their values as to what their precise meaning is.

I am aware of a page on a useful website which explains a number of those terse labels.  ;)

Quote
The PTM experiment would be very interesting.

I shall make a note to remind myself to perform the experiment.
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Weaver

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #7 on: October 06, 2016, 11:33:56 PM »

@ejs thanks for pointing that out. I wonder why the authors chose to ban HEC error correction.
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burakkucat

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #8 on: October 07, 2016, 09:16:58 PM »

The experiment, attempting to use PTM on a G.992.3 configured circuit, was performed. It was totally unsuccessful.  :(

No matter how I manipulated the configuration, a working connection was impossible to attain.  :no:

By the time I had finished the experiment, I had to resort to loading the saved configuration file to regain Internet access.  ::)
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Weaver

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #9 on: October 07, 2016, 10:20:08 PM »

It seems like a real missed opportunity. I wonder how many modems offer PTM as an option?
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burakkucat

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #10 on: October 07, 2016, 10:35:28 PM »

A little thought keeps niggling.  :-\  So much so, I have decided to try the experiment again at a later date when more time is available.
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Weaver

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #11 on: October 07, 2016, 10:58:36 PM »

Many thanks for that, it's good to know.

I realise now that this is perhaps only relevant in the case of TT DSLAMs, as presumably you are on TT LLU? (I'm assuming, don't know why, that TT is LLU-only? Is that the case?)

I wonder if any kitizens could test on ADSLx using a BT DSLAM?
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kitz

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #12 on: October 07, 2016, 11:02:07 PM »

Just seen this.   It definitely wouldn't work with BTw 20CN as they run an ATM backhaul.
Different framing methods and circuit paths. 
ATM uses VCs and VPs,  your connection is set up to run over a specific Virtual Path through ATM switches.
PTM uses HDLC and VLANs. ATM needs AAL5.

Put it into PTM mode and your traffic will go nowhere.
Square peg into round hole springs to mind.
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Weaver

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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #13 on: October 07, 2016, 11:06:31 PM »

Kitz, I'm aware this is true for 20CN. I'm 21CN ADSL2. And Burakkucat is * ADSL2. Is that true for him too, that ATM extends beyond the DSLAM ?

(The experiment is not open to G.992.1 users.)
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Re: HEC errors, non-reporting and PTM vs ATM on ADSL2
« Reply #14 on: October 07, 2016, 11:25:13 PM »

Without going into networking and protocol depth and the OSI model, ADSL2+ has a layer 2 switch 'behind' the MSAN. 
ATM is used on the link between modem and MSAN.
AAL5 is what does all the converting between Ethernet and ATM.. and then back again before it can go on to the 21CN backhaul.
Presumably TT uses an ethernet backhaul.

Theres a reason why ATM was invented and it has its advantages for ADSL.
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