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Author Topic: Crazy fault lost 2/3 sync speed.  (Read 4436 times)

kitz

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Re: Crazy fault lost 2/3 sync speed.
« Reply #75 on: July 11, 2021, 06:12:08 AM »

Ah, so original ADSL just didn't have any rate adaptation in the spec at all?

Thats right.  Going back to pre 2005ish and pre radsl,  then you could have a line that if it were on maxdsl may sync at 1.8Mbps.   But if you put that line on a fixed rate 2Mbps product then it wouldnt be able to sync.   The modem didn't do channel analysis, so couldn't even fall back to 1Mbps or 512Kbps.   The connection would just be dead.   

There was no real Dynamic LM nor DSM...  I dont think there was even a Target SNRM  - no need, because its the Target SRNM which is used to help calculate the sync speed.    Everything was fixed at the DSLAM whereby it was hoped you would have a 6dB SNRm 'buffer zone' sufficient to keep the line error free.  Didn't even have interleaving... only a FAST channel, so a noise burst would take a line down and it may not be able to sync back up again.  There was a guy in the Usergroup who had iirc 1Mbps and his connection could be down for days.   Eventually BTw downgraded the line to 512kbps.   
I'm sure Max would be in his element at the thought of no DLM....  until.... he realised the other technologies that are closely related to it and/or under its control.   Much as I hate the Openreach DLM and its stuck capping, I fully understand how it benefits the majority of lines and why we need a DLM.   
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kitz

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Re: Crazy fault lost 2/3 sync speed.
« Reply #76 on: July 11, 2021, 06:18:35 AM »

People (especially in the US) bad mouth DSL but its honestly amazing just how much its evolved over the years.

When I get time, I've got a post to  make about a friend of mine in the US and her broadband.    My jaw dropped when I found out how much she pays and what speed she got.  No joke, its like they are 10-15 years behind us.  It's worse than Weaver's connection and it's not as if she's far away from civilisation or anything.   
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Alex Atkin UK

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Re: Crazy fault lost 2/3 sync speed.
« Reply #77 on: July 11, 2021, 07:06:06 AM »

When I get time I've got a post to  make about a friend of mine in the US and her broadband.    My jaw dropped when I found out how much she pays and what she speed she got.  No joke its like they are 10-15 years behind us.  It's worse than Weaver's connection and not as if she's far away from civilisation or anything.   

When Louis Rossman was looking for new premises in New York, he literally said how the ISP he was forced to use in his current building was so bad he couldn't live stream.  In many respects its the high density cities that are the worst (the exact places its cost effective to go 100% FTTP) because there is no mandate for competition.  One building has the good ISP, another building has the bad one.  It really gives you an appreciation for how we deal with anti-competitive behaviour over here.  But were gonna need to split-off the thread if we keep going off topic like this. ;)
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #78 on: July 12, 2021, 02:15:45 AM »

Not really.  That was before rate adaptive dsl (radsl) technology became available.   Back then the modems didn't specifically analyse the channels & bit rates to work out the maximum speed that the line was capable of syncing at. 

The speed was fixed rate at the DSLAM and therefore the modem could either sync.... or it couldn't.  If there was insufficient bit load to maintain 2Mbps then the line would just not be able to connect all at.   So there were basic rules in place, mostly based on the attenuation which dictated whether you could get 256/512/1000/2000 kbps.   Obviously there were a few lines which may have had slightly better SNR and sometimes BT could be persuaded to try you on the higher speed. In those days your SNR was very important in deciding the max speed. 

Maxdsl was the first rate adaptive product offered by BTw.  Maxdsl allowed the line to negotiate a sync speed based upon the current line conditions by analysing each frequency bin based upon the target SNRM of 6dB.  Not all modems were able work properly with maxdsl without a f/w update.  iirc thats when I ditched my Solwise SAR110?

adsl2+ natively uses rate adaptive technology, but it also has better coding algorithms for overheads than adsl1 & adsl2 allowing a max 24Mbps.  In theory, the rate adaptive process should have been not much different from any of the adsl2+ products offered by most of the LLU ISPs at the time.  Even though the superior coding algorithm allowed adsl2+ to be more flexible with the target SNRM, most stuck to 6dB or 9dB (Tiscali).  Many of the BTw Maxdsl DSLAMs were actually MSANs capable of adsl2, but we are talking the days when backhaul bandwidth was still a problem - mostly using ATM 155/622Mbps pipes.

The exceptions were (1) Be* who technically didn't have a true DLM, but allowed a target SNRM of 3dB to be set at the MSAN.... and (2) I think it was UKO who  would allow 3dB profiles and also dabbled with SRA. 



I still remember my line not meeting the spec BT had specified to allow a 576kbit order to go through, but I was first on the exchange, engineer was excited as me so he tried it anyway and it worked. :)  The frog modem days.

SRA was such an amazing tech for lines that had inconsistent noise levels, it makes me wonder how much of an easier time Weaver would be having e.g. if he had SRA.
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Alex Atkin UK

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Re: Crazy fault lost 2/3 sync speed.
« Reply #79 on: July 12, 2021, 10:10:29 AM »

I still remember my line not meeting the spec BT had specified to allow a 576kbit order to go through, but I was first on the exchange, engineer was excited as me so he tried it anyway and it worked. :)  The frog modem days.

SRA was such an amazing tech for lines that had inconsistent noise levels, it makes me wonder how much of an easier time Weaver would be having e.g. if he had SRA.

I still have my USB ADSL modem knocking around, can't bring myself to throw it out.  Though by the time my exchange was enabled, consumer routers had already become a thing, I bought it separate for diagnostics.

I'm trying to remember what my first router was now, I think it was a D-Link, long before integrated WiFi was a thing. (I actually had a Belkin 802.11b Access Point when they first came out, it was practically unusable)

For many years though I ran on the Netgear DG834.  In fact, the first thread I posted on this forum was about that.
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #80 on: July 30, 2021, 02:17:36 AM »

Had the biggest storm i remember for a while a couple of nights ago, I checked my data the next morning and was lots of ES, but no DLM action, so either the wide area detection worked, or my new ES is so low now that I was able to absorb a few hours of storm and stay below the thresholds, is good. :)
« Last Edit: July 30, 2021, 08:24:34 AM by Chrysalis »
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Alex Atkin UK

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Re: Crazy fault lost 2/3 sync speed.
« Reply #81 on: July 30, 2021, 04:46:05 AM »

Fingers crossed.
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #82 on: September 16, 2021, 02:02:02 AM »

Well a new problem, but may be one I have to put up with depending on what happens whilst the line is interleaved.

My line just went down, and I noticed on the aaisp log the rate limit had changed, line is now interleaved but its not due to a burst of errors, Instead since around 9pmish on the 14th (day before yesterday) there has been a constant barrage of errors on the line, seemingly not service impacting as not noticed any actual problems, but obviously DLM doesnt know the actual service impact so am now interleaved.

Sync speed within product spec though so I probably cannot do anything about it unless I find the noise source.
« Last Edit: September 16, 2021, 02:05:35 AM by Chrysalis »
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #83 on: September 16, 2021, 07:38:07 PM »

I replaced cable, modem, psu, turned off ups, tried test socket (like how the new sockets just clip off), turned off my stb, and I dont think the noise is local.  Also unsurprisingly the GEA line test passes.

It seems to have no affect on QLN, hlog, or sync speed itself, just errors on the line, so I am now having to accept been interleaved for the foreseeable future. The bit of good news is even with the 100s of thousands of FEC and the thousands of CRC I was getting on fast path, the interleaving is mitigating 99% of them.  If I had g.inp I expect this would be a non issue.
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #84 on: September 19, 2021, 06:39:00 PM »

An update, I noticed my LAN cables were reporting errors so surely local, I turned of a few more devices and the FEC is zeroed, so I will probably know exactly which device it is very soon.
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kitz

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Re: Crazy fault lost 2/3 sync speed.
« Reply #85 on: September 22, 2021, 08:30:16 AM »

Interesting, so it could well be local.   Hope you manage to isolate.
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Alex Atkin UK

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Re: Crazy fault lost 2/3 sync speed.
« Reply #86 on: September 22, 2021, 09:13:58 AM »

I hope its something easily solved, would be annoying if its something essential and expensive.
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #87 on: September 22, 2021, 05:43:46 PM »

I was misled by the FEC going down to 0, that was because of the gap in the graph, seems the FEC momentarily goes down to 0 when there is a gap instead of just cutting off.

Some of the LAN cables are still getting a steady stream of errors, and its across multiple cables, even brand new replacements.  It is only happening on the shorter cat 5 cables, not the thicker long cat 6 I have.

The bitswaps have shot up across the entire VDSL2 range which seems to suggest it isnt just a specific frequency affected.
« Last Edit: September 22, 2021, 05:46:30 PM by Chrysalis »
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Chrysalis

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Re: Crazy fault lost 2/3 sync speed.
« Reply #88 on: October 11, 2021, 02:00:43 PM »

Couple more updates, the first which is an old update but I forgot to post it.  I discovered the errors on the LAN stop if I disconnect the modem from the rest of my network, they also stop if I keep the modem connected but disconnect the modem cable.

The second update its a hopeful one, but might be related, there has been a faulty street light outside my property, the council finally got round to investigating it and they say it has a electrical supply fault, I asked them where the power fed from and the direction they pointed in goes right past my BT pole.  I got no idea when it will be fixed though.
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Weaver

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Re: Crazy fault lost 2/3 sync speed.
« Reply #89 on: October 21, 2021, 11:39:04 AM »

It sounds like an evil modem, no? It shouldn’t be letting interference through. Is it injecting rfi into the LAN?

If BT are informed, will that help to put pressure on the council?
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