Any ADSL experts here?

Thread Starter

ApacheKid

Joined Jan 12, 2015
1,609
I have some questions about ADSL2+ and a strange story to recount about my conversation with an engineer yesterday. The more in-depth your knowledge of ADSL the better, I know rather little myself.
 

MisterBill2

Joined Jan 23, 2018
18,477
Several years back I called for technical advice about a DSL installation. The person was NOT an engineer by any definition, and knew much less than I did about DSL. And I did not know much at all. Spare no details, tell us everything.
I also await the strange story.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
1,609
A strange story. Waiting for it.
A week ago our internet suddenly became very unstable, constantly getting errors with browsing, conferencing, remote desktop and so on. I logged into the modem and could see repeated attempts to "retrain" and high (looking) CRC error rates.

The modem would establish the connection, settle down for 5, 10 perhaps 30 minutes then wham, repeat. After around four or five hours it settled down and was stable once again, all was good.

Then we began to notice sluggishness so to speak, during the day stuff that was usually instant was dragging. Opening certain sites, refreshing an inbox and so on, these started taking 5, 10 or more seconds whereas ordinarily we were not conscious of any delay.

I logged into modem and saw download speed 8.607 Mbps and upload speed of 0.268 Mbps - this caught my eye. Perhaps the system had gradually reduced the upload rate as it strived to reduce the error rate and eventually became stable at that low upload rate.

1653663292922.png

So yesterday I had an engineer dispatched, the customer service person confirmed "This is a problem at "our end" not likely your property, we'll send an engineer who might need to access your home but it looks external".

Anyway he turned up later and began to summarize his findings. He said this was likely unavoidable, getting the signal across this distance (from the hub several thousand feet away to my house) was asking a lot. He also said the infrastructure was actually VDSL and several customers had had ADSL "overlayed" so to speak onto this VDSL infrastructure.

He mentioned that new subscribers are likely being added and that this is starting to impact the quality of the ADSL lines or links.

This doesn't sound right, we've had this ADSL internet for eight years and it has been actually damned stable and reliable. He hinted that getting internet in my area was a challenge and that I might want to look at alternatives (he mentioned a cell based fixed wifi system that runs over 5G).

I pressed him politely and he was patient and tried to explain more detail but my technical knowledge of ADSL and stuff is vague at best so I wasn't able to clearly grasp the problem.

I argued that we pay for a certain standard of service and CenturyLink are surely contractually bound to deliver that irrespective of any infrastructure shortcomings. He kind of agreed too.

We ended the chat by him giving me the cell of a fellow engineer who was much more skilled with ADSL and said this guy would certainly be able to review this and get back to me with a solid detailed answer, perhaps even be able to fix it but that was unclear at this point. He left me his card too and cell. He did say to go straight to him, not to waste time requesting an engineer through the usual website/service desk!

He was as helpful as I could expect and patiently chatted with me for 45 minutes as we chatted in and out of technical areas. He did seem though kind of resigned to the fact that the setup ADSL on top of VDSL and the distances was not idea and was the root of the problem.

I'm going to leave this until early next week and then contact this other engineer and see if he can explain better, my position is that this is a fault whether it be a broken wire or an entire infrastructure sub-system and that the fault must be rectified.

Final note, this morning I re-powered the modem and it has recovered and settled down but the slightly higher upload speed of 0.418 Mbps, almost double.

1653664437234.png

In both image the various counters have recently been reset to zero.
 
Last edited:

nsaspook

Joined Aug 27, 2009
13,265
In the ancient past I had private ADSL and managed TELCO digital services landlines in military so I'm familiar with the basic technology and terminology as a technical controller in a TCF.

Most of the copper infrastructure is decrepit here, with buried lines decades old, in vaults filled with nasty water. It took a few trials on a few different CO wire POTS pairs to get a reliable link that still degraded when the ground was saturated with water and got better when things dried out. They can roll a truck to test possible spare pairs from the DSLAM or CO to your house local POTS loop punch-down block. If your house local loop is bad then you're likely SOL for a pair replacement there.

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https://support.novell.com/techcenter/articles/nc2000_08c.html
 

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Thread Starter

ApacheKid

Joined Jan 12, 2015
1,609
In the ancient past I had private ADSL and managed TELCO digital services landlines in military so I'm familiar with the basic technology and terminology as a technical controller in a TCF.

Most of the copper infrastructure is decrepit here, with buried lines decades old, in vaults filled with nasty water. It took a few trials on a few different CO wire POTS pairs to get a reliable link that still degraded when the ground was saturated with water and got better when things dried out. They can roll a truck to test possible spare pairs from the DSLAM or CO to your house local POTS loop punch-down block. If your house local loop is bad then you're likely SOL for a pair replacement there.

View attachment 268134View attachment 268135
https://support.novell.com/techcenter/articles/nc2000_08c.html
This is helpful, informative.

Thanks.

PS: What is your avatar depicting? a family member who practices a MA?
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
1,609
Yes, It's my 'baby' girl practicing for her Black Belt in MA.
Let me see your 'War' face!
View attachment 268141
Good for her, I trained Wing Chun under Simon Lau in london quite a few years ago and there were several female students, not to be messed with!

This is part of a British documentary he featured in called Way of the Warrior from the early 1980s. You'll see several female students.

 

nsaspook

Joined Aug 27, 2009
13,265
Good for her, I trained Wing Chun under Simon Lau in london quite a few years ago and there were several female students, not to be messed with!

This is part of a British documentary he featured in called Way of the Warrior from the early 1980s. You'll see several female students.

Needs a longer belt display.
PXL_20220527_180613211.MP.jpg
She's mainly practicing grappling techniques in the wait for her Taekwondo Black Belt trial.
https://taekwondo.fandom.com/wiki/Taekwondo_Grappling
 
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Tesla23

Joined May 10, 2009
542
He mentioned that new subscribers are likely being added and that this is starting to impact the quality of the ADSL lines or links.

This doesn't sound right, we've had this ADSL internet for eight years and it has been actually damned stable and reliable. He hinted that getting internet in my area was a challenge and that I might want to look at alternatives (he mentioned a cell based fixed wifi system that runs over 5G).
I have no direct experience, but from my understanding of ADSL this may be true.

Crosstalk is one of the big DSL issues, it's (now) comparatively easy to send reasonable datarates over a single POTS cable pair. When you have many such pairs in a bundle, sending broadband signal down one pair tends to produce crosstalk to nearby pairs in the bundle. For various reasons, near-end crosstalk tends to dominate, so signals that the node is sending down your pair tend to interfere with signals the node is trying to receive from other pairs, potentially impairing the uplink of others. Consider what happens if a new DSL user has a pair closely coupled to your pair, and perhaps that user is further away than you so that the node is sending a much stronger signal to them. That could suddenly introduce significant crosstalk that would affect your uplink. So it's feasible.

If your expert concludes it is crosstalk then there may not be a lot you can do if your carrier isn't obliged to improve your service. Maybe you can chat up a tech and see if there is a spare pair going back to the node and try switching to that.
 

MisterBill2

Joined Jan 23, 2018
18,477
One thing not mentioned is the possibility of some change in the subscriber physical system, such as an added phone without the required filter in line. It might even be one added without anybody else being aware of it. Of course this is a guess, but having a worse signal to noise ratio is able to degrade performance. The local physical system is the one portion that the TS is able to address, I presume. And certainly the use of the same like by others will degrade performance. One neighbor downloading movies or watching on-line videos degrades my speed quite obviously. So that is another possible cause.
 

nsaspook

Joined Aug 27, 2009
13,265
One thing you can do (if all else fails) is to pay for another copper line DSL capable phone number for a short period of time. I had two landlines to the house when I used DSL. One was used as the normal POTS phoneline, the other was dedicated only for DSL on basic cheap service, no long distance or anything else. This will force them (a CO work ticket and truck roll) to try to find another working pair for the install and maybe in the process cleanup the original line.
 
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