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Author Topic: ADSL1 vs 2  (Read 1111 times)

Taurit

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ADSL1 vs 2
« on: February 26, 2017, 04:23:40 PM »

Hello all,

I have an interesting issue(to me at least ;D), with the differences between ADSL1 and 2. From most posts I've read here and elsewhere online it's always recommended to use ADSL2 as it uses the same range of frequencies, but is a more advanced spec and so should be more reliable. However in all testing on my talktalk line forcing g.dmt generates a higher sync speed(4.2mb vs 3mb) and higher throughput than the alternative, and I usually leave it in g.dmt.
When reconnecting with g.dmt the noise margin remains at or close to 6.0dB. ADSL2 starts at 6.0dB, but within 60 seconds has jumped up massively to 12 or even 14dB, which slowly drops to 9dB over a couple of weeks.
As I have quite a long line (54dB / 4.4Km) I very rarely try ADSL2+ as it offers the lower performance of the three.

Am I misunderstanding how the different modes work and how modems report the margin? Or is there a fault with my equipment or line? If anyone else has experienced similar effects should I just leave it in what works? I'm concerned that at some point ADSL1 may become unsupported and leave me with poorer performance.

Thanks
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tickmike

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Re: ADSL1 vs 2
« Reply #1 on: February 28, 2017, 11:02:55 PM »

Hi, Welcome to the forum.
You probably have seen one of my posts where I found that my ADSL2 line worked better and more stable by forcing the  HG612 modem in ADSL mode.
I have a long line 4.3kl , Line attenuation (dB):     52.0      31.5  .
You can see the SRNMargin graph when I switched over to ADSL the other day.

Can you install DSLstats and give us some graphs and details about your line and modem etc

http://dslstats.me.uk/
« Last Edit: February 28, 2017, 11:15:22 PM by tickmike »
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Weaver

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Re: ADSL1 vs 2
« Reply #2 on: March 01, 2017, 12:52:56 AM »

Taurit, that's very unusual, and the only thing I can think of is that perhaps it is to do with _variability_ at the higher frequencies, so that cutting them out will protect you from very high error rates that cause DLM to kick in and penalise you, but I'm not even sure if that argument makes sense, I would need to think about it much more.

I have had the opposite experience, on three lines that are much weaker than yours (66 dB d/s attn, ~4.55 mi long.) Upgrading the exchange gave me quite a speed improvement and then ADSL2 gave me a modest further improvement. (Modems are locked to ADSL2-only, to not even think about trying ADSL2+, which is nowhere near relevant anyway).

As always, it would be interesting to try different filters, then different modems. In this odd case, it makes me wonder if there is a chance the modem might just have better software for dealing with G.992.1 / ADSL1.
« Last Edit: March 07, 2017, 07:45:57 AM by Weaver »
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Taurit

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Re: ADSL1 vs 2
« Reply #3 on: March 06, 2017, 12:53:53 PM »

Hi, I've installed dsl stats and got a little bit of information for you.
Code: [Select]
Stats recorded 06 Mar 2017 12:29:31

DSLAM/MSAN type:        IFTN:0x71c8 / v0x71c8
Modem/router firmware:  AnnexA version - A2pB025f.d22k
DSL mode:                ADSL2
Status:                  Showtime
Uptime:                  7 days 22 hours 10 min 23 sec
Resyncs:                0 (since 06 Mar 2017 12:14:59)

Downstream Upstream
Line attenuation (dB):  53.5 33.3
Signal attenuation (dB): Not monitored
Connection speed (kbps): 3043 763
SNR margin (dB):        13.7 6.1
Power (dBm):            0.0 12.9
Interleave depth:        16 8
INP:                    1.08 1.22
G.INP:                  Not enabled Not enabled
Vectoring status:        Unknown

RSCorr/RS (%):          0.0019 2.5134
RSUnCorr/RS (%):        0.0001 0.0000
ES/hour:                0 0
Router is a Billion 7800n, with latest firmware ( 1.06h.dt2 ), and I've not seen any reports on their forums about similar issues. I've tested with a Linksys WAG160N in the past with similar results(this was a few years ago mind), the other modems I have are the original Talktalk (SmartAX MT882) and a Belkin F5D7630, are either of these known to have a "better" chip than the Billion?
I've got my router connected to the phoneline via a small maplins surface mounted box, being the only extension on the line(and twisted pair not the flat extension sort). Interestingly enough connecting direct into the test socket produces a slower sync speed than on the extension(3.5M vs 4M on ADSL1).

I've attached screenshots of the QLN and bitloading graphs after leaving the connection running for a week, hopefully these will be what your after, I'm going to leave dsl stats running for a day or so and will post the snr margin if it helps.
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Weaver

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Re: ADSL1 vs 2
« Reply #4 on: March 07, 2017, 08:01:50 AM »

A few things: Your extension vs direct thing is impossible (supposedly, apart from some really exotic possibilities that I haven't worked through thoroughly), but what do I know. It could be a false result do to DLM, because I have had this myself. Different filters? It would be worth measuring twice, and always power off for 30 mins before measuring, to avoid DLM's wrath.

Your downstream sync speed seems a bit rubbish compared with mine, given that you have a downstream attn ~13dB better than mine. The enormous d/s SNRM is to blame. Need to sort that out. It is evidence of DLM punishment unless someone at the ISP has imposed some strange settings. Perhaps too much testing / swapping kit without following the half-hour-off rule?

The enormous noise peak at ~650 kHz isn't helping, being an amazing 50dB high, it's killing off a chunk of spectrum.
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Weaver

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Re: ADSL1 vs 2
« Reply #5 on: March 07, 2017, 08:06:58 AM »

Kitizens - what exactly does the INP figure refer to in Tauritís modem stats? I take it this is the 'derived parameter' in G.992.3 Table 7.7, am I correct?

A value of 1.08 doesn't sound particularly impressive but then I have nothing to compare it to. What do you all have?

Could we bung the interleave depth up? I wonder if this would help tame DLM?

Two questions for Taurit then: what is your interleave depth setting? Would you mind it being increased to give you worse latency but more speed and better reliability?

Taurit, if you are measuring sync rates, you will need to note the SNRM at the time, so that we are comparing like with like. I'd the target SNRM changes, then that will explain misleading sync rates.
« Last Edit: March 07, 2017, 08:27:53 AM by Weaver »
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burakkucat

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Re: ADSL1 vs 2
« Reply #6 on: March 07, 2017, 07:14:27 PM »

I am also a fellow user of G.993.2 (due to the length of the metallic pathway).

Here is the very latest data for my circuit, harvested just a moment ago --

Code: [Select]
$ xdslctl info --show
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason: 8000
Last initialization procedure status: 0
Max: Upstream rate = 992 Kbps, Downstream rate = 5796 Kbps
Bearer: 0, Upstream rate = 984 Kbps, Downstream rate = 5120 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): 6.6 6.3
Attn(dB): 45.0 28.2
Pwr(dBm): 0.0 12.7

ADSL2 framing
Bearer 0
MSGc: 59 12
B: 160 30
M: 1 4
T: 1 4
R: 16 10
S: 1.0000 4.0000
L: 1416 268
D: 32 8

Counters
Bearer 0
SF: 1266124 211086
SFErr: 129 0
RS: 82297992 3396907
RSCorr: 9479 289
RSUnCorr: 2202 0

Bearer 0
HEC: 1662 0
OCD: 2 0
LCD: 2 0
Total Cells: 248447052 47642605
Data Cells: 9831107 649192
Drop Cells: 0
Bit Errors: 134519 0

ES: 59 0
SES: 0 0
UAS: 46 46
AS: 20573

Bearer 0
INP: 1.00 1.00
INPRein: 0.00 0.00
delay: 8 8
PER: 16.25 18.00
OR: 32.00 8.00
AgR: 5131.95 988.14

Bitswap: 4087/4087 38/38

$
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Taurit

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Re: ADSL1 vs 2
« Reply #7 on: March 07, 2017, 07:30:25 PM »

Hi,
as promised a couple of graphs showing my SNR over 2 hours and 24 hours. From my view it doesn't look like there's any sharp changes, this is with the default dslstats settings 30s(would reducing the sampling interval help further?). I don't think there's any issue with the line from a stability point, just when ADSL2 is selected(or left in auto select mode).

As far as I know the interleave is set to auto - presume whatever the DLM decides what is most appropriate. If anyone is aware of a particular command or setting to force different interleave then I'm willing to try.
Yes I'm well aware of the "interference" at 657Khz, I can blame BBC Radio Wales for that, I just hope the old MW transmitters go silent one day  :)
Admittedly whenever I've tested at the master socket it has only been for brief periods in order to rule out line faults on the extensions, so DLM could be a factor. My thought is that there may be some faulty electrical equipment nearer the master socket that it doesn't pick up when on the extension.

I'd always wondered what the accepted waiting time between disconnecting and reconnecting was, so will wait 30+mins between trying different settings from now on. Lets hope that improves things a little.
With the line now being up for 9 days, I'll try a resysnc and post the fresh connection stats shortly.
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ejs

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Re: ADSL1 vs 2
« Reply #8 on: March 07, 2017, 07:44:44 PM »

@Taurit

The HLog graph might be useful, to see if it shows any obvious line problems.

Considering that the QLN data is only collected while the modem is training up, and that ADSL2 initially connects at a 6dB SNRM, which then rises shortly after, it's almost as if that huge spike of noise on the QLN graph is only present while the modem is training in ADSL2 mode. The interference seems too wide for what might be expected from a radio station.

I don't think the problem is anything to do with DLM or interleaving parameters or anything like that, it sounds like some weird sort of line fault, faulty equipment at one or other end of the line, or faulty interaction between the equipment at each end.
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Weaver

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Re: ADSL1 vs 2
« Reply #9 on: March 07, 2017, 08:12:22 PM »

Is it not the case that the target SNRM has got DLM'ed up to 12dB? Sorry, I've probably missed something from earlier.

I thought about DLM revenge due to plugging/unplugging when Taurit was doing the extension testing, something that has zapped me personally when I've been doing too much mucking about in one day without following the kitz rules.
    http://forum.kitz.co.uk/index.php/topic,15905.msg307641.html

Whatever, unless I'm way off, if your target SNRM is 12dB will have to wait for ages for DLM to forgive you if it's due to testing-related sin, but if it's a bad line then it's never going to come down until you get the line mended, or internal wiring, interference, filters, modems etc sorted out. Do all testing straight into the master socket with a high quality eg Tandy short cable or even straight into the test socket with no filter and a short good BT-to-modem cable as that rules out all wiring and filters temporarily. Recommend BT faceplate-type filter, and Tandy ultra-short cables to maximise the last drop of performance and give us rule-out.

Absolutely agree with ejs about the peak being too wide for a radio station, and the wrong shape, unless I'm going mad. Guys, what about intermodulation between a radio station and other noise? Would that work? If so that means a non-linear element inline which is easy enough to arrange.

About interleave some ISPs can set interleave on/off/auto on BTw 20CN, but if I remember correctly that's it, there are not different levels. I think I being BTw 21CN get three levels for downstream, off, low and high or something, and I can't remember about auto. I have locked mine on to "on" as opposed to auto, and it's on high or whatever it's called. LLU will presumably be something else.

Burakkucat will be on LLU? So not comparable in some respects.
« Last Edit: March 07, 2017, 08:16:06 PM by Weaver »
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Weaver

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Re: ADSL1 vs 2
« Reply #10 on: March 07, 2017, 08:21:14 PM »

Apologies, I've seen it now, very woozy. The noise figure jumps up at some point. What is that all about? What is the significance of that point in time? Some badness appears and doesn't go away.

So ignore a lot of the nonsense in my previous posts then. Your target SNRM is not 12dB, I take it.
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Weaver

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Re: ADSL1 vs 2
« Reply #11 on: March 07, 2017, 08:33:10 PM »

Tickmike made a good point back there. Unless his case is about a modem that is just rubbish at ADSL2/2+ in software terms (unlikely surely), maybe this is an example of Burakkucat's theorem.

Burakkucat advised me to try locking my modems to G.992.3 (ADSL2) only, not auto which might allow ADSL2+. The line is far far too slow to need ADSL2+ anyway. I'll let him tell the story.

But Tickmike would have to have a less clean line compared with mine given that his downstream attenuation is miles better than mine and I can do ADSL2 fine and don't need to lock mine down to ADSL1 to get the benefit of the Burakkucat theorem. Not at all impossible because mine is presumably exceptionally clean per metre because of the total lack of any kind of electrical noise along the critical final ~3.5 miles given that there is no electricity-powered kit anywhere near the copper.
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Taurit

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Re: ADSL1 vs 2
« Reply #12 on: March 07, 2017, 08:54:19 PM »

Wow I go offline and there's a list of responses to read  :)
Again this connection is using ADSL2(so as to get a fair comparison to the line before) - This time with a sync speed of 3800kbps and SNRM of 8.5dB. So it does look like the waiting 30mins is something I should've done prior to posting.
Code: [Select]
Stats recorded 07 Mar 2017 20:45:07

DSLAM/MSAN type:        IFTN:0x71c8 / v0x71c8
Modem/router firmware:  AnnexA version - A2pB025f.d22k
DSL mode:                ADSL2
Status:                  Showtime
Uptime:                  16 min 3 sec
Resyncs:                1 (since 07 Mar 2017 20:26:40)

Downstream Upstream
Line attenuation (dB):  53.5 33.2
Signal attenuation (dB): Not monitored
Connection speed (kbps): 3815 763
SNR margin (dB):        8.4 7.2
Power (dBm):            0.0 12.9
Interleave depth:        32 8
INP:                    1.22 1.22
G.INP:                  Not enabled Not enabled
Vectoring status:        Not monitored

RSCorr/RS (%):          0.0056 0.0000
RSUnCorr/RS (%):        0.0008 0.0000
ES/hour:                0.81 0.35
I've attached the HLog, tones after reconnection and the climb in SNRM after a reconnect. It was left closer to a hour before switching on for a minute then reconnecting the phone line, hope they help clarify my line a little. I'm afraid I don't understand the Hlog graph, I couldn't see any pages on the wiki before posting so don't know what a perfect graph should look like.
As you can (just about) see the SNRM climbs very quickly from 6 to 8.5db after connecting, so an improvement, but still on ADSL1 this behaviour doesn't exist.
I'm a little surprised that the spike in QLN isn't attributed to the MW transmitter, I should've mentioned earlier that the transmitter in question is less than a mile away and broadcasts perfectly with the missing tones.

Again if there are any further graphs(through DSLstats or otherwise) then I'll happily post.
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ejs

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Re: ADSL1 vs 2
« Reply #13 on: March 08, 2017, 04:57:29 PM »

The HLog graph is probably OK, the dip at about the point between the upstream and downstream could merely be due to measurement error (I think the transmit power tends to be reduced on those tones to prevent interference between the upstream and the downstream). Similarly, there's a weird bit on the HLog graph at the point where the noise is strongest, but that could be due to the noise being so strong that it makes it difficult to measure the signal accurately.

The interference from the MW transmitter does seem too wide, but could mostly be due to your proximity to the transmitter. It looks like you could pick up the signal with a radio tuned anywhere 600-700kHz.

I think I may have misinterpreted the apparent rise in the SNRM shortly after connecting. It probably doesn't actually mean anything much, besides that the SNRM is not accurately reported very shortly after connecting. So it may actually be due to a different target SNRM after all.
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burakkucat

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Re: ADSL1 vs 2
« Reply #14 on: March 08, 2017, 07:07:53 PM »

The HLog graph is probably OK, the dip at about the point between the upstream and downstream could merely be due to measurement error (I think the transmit power tends to be reduced on those tones to prevent interference between the upstream and the downstream).

That is perfectly normal for a G.992.{1|3|5} circuit.

Quote
Similarly, there's a weird bit on the HLog graph at the point where the noise is strongest, but that could be due to the noise being so strong that it makes it difficult to measure the signal accurately.

I agree.

Quote
The interference from the MW transmitter does seem too wide, but could mostly be due to your proximity to the transmitter. It looks like you could pick up the signal with a radio tuned anywhere 600-700kHz.

My feeling is that any non-linear circuit would pick up the transmitted signal, being such a high signal strength area. I suspect that all semiconductor devices are being driven in the direction towards junction saturation. (Even dental amalgam, oral bacteria and saliva would probably pick up the transmission!)
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