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Author Topic: Line Attenuation !!!  (Read 7897 times)

Trolltamer

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Line Attenuation !!!
« on: July 05, 2006, 10:48:29 PM »

Hi All,

New to the forum, but have found it VERY informative ... ty kitz.

I am on ADSL MAX with BT for my sins.... 6 weeks of HELL SO FAR.......... :evil:

I've had syncs of 4mbps down to 160kbps unfortunatly more the latter..

from samknows.com  i'm less than 1.7km from exchange and told i have 4.42 km line (BTw) and showing 63.5db line attenuation down and 31.5 up, 3 BTw engineers and 3 half days of work!!!! when the router is plugged into adsl 1.0 master socket fitted by bt!!!!!<wonders how the fault is in my premises!!!!!>

Just wondering why my line attenuation is SOOOO high .... I've been on a 6km line showing 60db.

I  have been told by INDIA TWICE i was getting a new line run from the cabinet to the exchange (which i thought HIGHLY unlikely!!!!)

<<i'm nearly ready to throw in the towel and go back to fixed 1mb as at least it was usable all the time.... if i remember rightly my line attenuation up/down was nearly the same in my old property, just wonderd what others are like and what speeds are being achieved ???? i have tried 3 routers BT2500V seem to be the most stable, DG834GT latest firmware won't sync and hold at all over 512kbps but does sync 4mbps plus BRIEFLY and old BT220 router which syncs and hold for a few hours
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kitz

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Line Attenuation !!!
« Reply #1 on: July 06, 2006, 10:14:08 AM »

>> 63.5db line attenuation

ouch especially considering 1.7km as the crow flies. :/

Attenuation is in relation to line length (although it can vary slightly depending upon which router you use). But on the whole there is nothing much that the customer can do about attenuation.
Its not unknown for actual line length to be double the *crow flies* length, and some lines can and do go all around an estate before it can reach a particular home.

>> i was getting a new line run from the cabinet to the exchange

This one is interesting and it depends upon your locality and what options are available to the BTw engineers. An alternative route may or may not be possible and isnt something that BT always do.

However having said that I personally know someone who did manage to get rerouted.
One of the things that she noticed was that on her side of the road, the BT checker was stating that only 512kb-1Mb was possible, where as across the road, they could easily get 2Mb.
In her circumstances it appeared that anyone on the RH side of the road was first routed around a very large estate. Whilst those houses on the other side, came through from an entirely separate cab and which had a more direct route back to the exchange.
After months of hassling BT * she finally managed to get them to reroute her line through the other cab which gave a more direct route overall to her house - this sounds perahps similar to what BT are suggesting for yourself?



It may be interesting to do some ground work and get hold of some neighbouring phone numbers and see what the BT checker says about the estimated speeds, you may be lucky and find like she did that the long line length only affected *her side*, and then if *the other side* is better, then there is another way that bt can route you.
If you find some neighbours phones are giving much better estimations or even line stats than your own then the better chance you have of getting this sorted.

I wish you good luck

* I should also point out that she was also reporting problems with the voice quality/noise of the line too.

>> i'm nearly ready to throw in the towel and go back to fixed 1mb

A year ago a lot of people were excited about the prospect of dslmax, the theory was that it would give each line the best/highest speed that was was possible.
However, the reality over the past month or so has seen some users on long lines having horrendous problems that certainly were not anticipated.  There are still some problems with max and hopefully BT will be able to get these ironed out.
However, in the meantime I do know of some users who have requested to go back onto a fixed speed product to get stability on the line.
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chris87

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Re: Line Attenuation !!!
« Reply #2 on: July 11, 2006, 01:27:40 AM »

Quote from: "Trolltamer"
Hi All,

New to the forum, but have found it VERY informative ... ty kitz.

I am on ADSL MAX with BT for my sins.... 6 weeks of HELL SO FAR.......... :evil:

I've had syncs of 4mbps down to 160kbps unfortunatly more the latter..

from samknows.com  i'm less than 1.7km from exchange and told i have 4.42 km line (BTw) and showing 63.5db line attenuation down and 31.5 up, 3 BTw engineers and 3 half days of work!!!! when the router is plugged into adsl 1.0 master socket fitted by bt!!!!!<wonders how the fault is in my premises!!!!!>

Just wondering why my line attenuation is SOOOO high .... I've been on a 6km line showing 60db.

I  have been told by INDIA TWICE i was getting a new line run from the cabinet to the exchange (which i thought HIGHLY unlikely!!!!)

<<i'm nearly ready to throw in the towel and go back to fixed 1mb as at least it was usable all the time.... if i remember rightly my line attenuation up/down was nearly the same in my old property, just wonderd what others are like and what speeds are being achieved ???? i have tried 3 routers BT2500V seem to be the most stable, DG834GT latest firmware won't sync and hold at all over 512kbps but does sync 4mbps plus BRIEFLY and old BT220 router which syncs and hold for a few hours

your not alone mate mines 61  :cry:
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soms

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Line Attenuation !!!
« Reply #3 on: August 05, 2006, 07:36:21 PM »

i'm not on DSLmax, but am considering it. roughly 2 - 3 miles to the exchange by rural road (cables most likely follow these? BT have had the man hole covers up in the past) on 512k reg ADSL line attenuation 63, SNR margin 16 at best with all internal optimisations.

Again from reading here tempted to ask the neighbours to let me look at their line stats and see if we are just unlikely or if everyone is stuck in the same boat.

Are there any external influences on attenuation like there can be with SNR or is it just line length?

Also have to unplug/replug router few times a day to keep the connection running. Seems to be a real stability issue. When the problems occur, DSL is still synced.
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kitz

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Line Attenuation !!!
« Reply #4 on: August 05, 2006, 08:53:28 PM »

hi soms

>> attnt 63
>> SNR 16 at best

How low does that SNR drop?  
I hate to say this, but personally if that was my own line I would leave maxdsl alone right now.

Max still has a lot of problems that need ironing out, and most of those problems are occuring on the longer lines, and things are not quite turning out as perhaps they should.

The reasons why I have doubts with those particular stats are as follows

If your SNR Margin is 16... then..
A crude estimate of what your line is capable of is 1080kbps (kilo bits per second).

If your SNR Margin drops to 10dB.. then..
A crude estimate of what your line is capable of is 570kbps (kilo bits per second).
(taken from here)

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If at best you manage to sync at 1080, the times when your snr margin drops lower..  and because of the way the bRAS profile is set, you will still be limited to a throughput speed of 512kbps.
(see maxdsl bRAS table - bottom of page).

In the meantime during the training period you will very likely see frequent disconnections, and variations in speeds.  You are also most likely to have interleaving turned on which will slightly affect your latency.

Therefore based on the info that we have on your line, you are unlikely to be much better off Im afraid.

>> Are there any external influences on attenuation.

Not really its mostly down to line length - although internal telephone wiring can affect this.. or perhaps if you have a fault on your phone line. Generally speaking attenuation is fairly static.

Since you mention that you have a few problems already.. I honestly think you would be best right now staying on the traditional product.. or at least until BTw sort out some of the existing stability issues.

tbh Ive seen a couple of people who have previously had stable 1Mb lines, suddenly reporting speeds of less than 512 kb or even 256 on occasions because of the way the bRAS profile works.
Ive also seen a few mumblings of late saying that max should perhaps now only be put on lines that could previously handle 2Mb or maybe 1Mb - .. simply because its the users that couldnt previously get the higher speeds that are having the worst time on MAX. :/

----
Bear in mind I could be wrong.. and you may just eke in a 1Mb connection..  its a risk you take with max..  but from info provided the odds are that your line is not best suited.
Normally Id recommend you try see if you can push the SNR up more, but it seems like you have already done all you can on your side of things.

Sorry to be the bearer of bad news :(
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soms

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Line Attenuation !!!
« Reply #5 on: August 05, 2006, 09:42:46 PM »

Quote
Sorry to be the bearer of bad news :(


No worries! My dissapointment is limited as for now 512k is fine for me, though it is a downer to know that others on your exchange could be getting almost a full 8meg downstream.

Quote
How low does that SNR drop?


Well it depends on the router. I am presently using Linksys WAG354G, and for example, the SNR is down to 12dB atm. That was also the more normal figure before i did the disconnect ring wire trick to the socket i use for my ADSL, which is fed a dedicated shielded link from a BT ADSL v1.0 master adaptor (The line box is in the attic :( ).

With my previous router, US Robotics 9106, before ring was disconnected, I was getting about 11dB on sync but constant PPP failures and no connection at all.

If i were to find out what kind of attenuation stats my neighbours were getting, is it likely there would be any kind of case with BT for line improvements? The voice quality is fine, so if there was a fault it would not be self evident. I know BT really dislike people approaching them about broadand problems, particuarly non-BT broadband customers since they only supply the service on wire. However I have done all i can to optimise my internal wiring. It now only seems to be the phone line which can be the problem. I do not mean to put you on the spot when i ask if you know of anyone who has been in this position and found any sort of  action that BT could do to improve the line?

Again, first, before even thinking of approaching BT i would like to check a neighbours stats and see what is going on. If they also have terrible stats, is there any "community" action that could lead to line improvements? (again, another really bad question) as I mentioned, we are less than 3 miles from the exchange, and I really think the line length cannot be a great deal more than that. Thanks for your help so far!
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kitz

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Line Attenuation !!!
« Reply #6 on: August 05, 2006, 10:36:19 PM »

>> If i were to find out what kind of attenuation stats my neighbours were getting,

Its certainly worth giving it a try... and no harm in asking BT...  but unless yours is very much different than theirs then you may well have a fight on your hands.
Its certainly worth seeing what speeds they are syncing at..  and if they are getting higher speeds than you .. then yes by all means give it a go.

>>  when i ask if you know of anyone who has been in this position

I know of someone who has sort of been in a similar position..  the post about it is in this thread... it took a few months and shes a pretty persistant lady and she did manage to get her line rerouted..  bear in mind it depends if they can reroute.
The case I mentioned in my post above though was a result of being about 1.5 - miles from the exchange by straight road...  but her line came all through a fair size estate first, which put a heck of a distance on it.

excuse my 1337 drawing skillz but her situation was like this
blue = exchange, red = house, green=cabs.
The drawing isnt accurate/scale, but just to give you an idea of what was happening in her case.

Her original line came off the middle cab..and came practically *round the back*... it was rerouted to come off the 3rd. Hope this makes sense.





I suppose you best bet would be to see if you can find out which route your line takes..

Another factor to bear in mind is.. Quality of the line also depends on how much copper is in the wire..  at one point BT substituted with other metals/alloys (aluminium) which meant that these lines make poorer quality adsl lines..  and there isnt that much that you can do about that.. since BT are obviously very reluctant to relay lines with aluminium joints because of cost.
TBH though the cabling quality is something I dont really know much about. :/
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soms

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Line Attenuation !!!
« Reply #7 on: August 05, 2006, 10:55:19 PM »

That drawing wasn't so bad! Demonstrated the story perfectly.

I will see what i can work out, here i'm in a small a village, totally seperate from the large village where the exchange is, and with aanother small village inbetween us. In our village we have one main street with a few odd roads going off in different directions, though very few properties are down these roads. I recon our "main" lines from the exchange come along the main lane from the exchange village and intermediate village and then run down the main street underground, with cables then coming aboveground here and there on poles, to junction boxes and overhead drop lines. Our street is  one of the minor streets, so our cables from the main street are overhead only, and we have no cabinets either, which makes it a little ess complicated, but not soeasy to see what is going on in some ways. I recon this is the main route of the cables because the terrain is hilly and the main access road is full of mainhole covers, which i know will also be for the mains water supply.

Thanks for the help again and btw the website is great. Very informative with all the links for the additional info and products anyone needs to troubleshoot and understand their ADSL. thanks again.
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Trolltamer

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Line Attenuation !!!
« Reply #8 on: August 14, 2006, 01:35:29 AM »

System Up Time 52:26:16
Port Status TxPkts RxPkts Collisions Tx B/s Rx B/s Up Time
WAN PPPoA 871535 1399478 0 1294 9678 52:19:45
LAN 10M/100M 2020090 1362229 0 11721 1732 52:26:11
WLAN 11M/54M/270M 0 0 0 0 0 00:00:00
 

ADSL Link Downstream Upstream
Connection Speed 3488 kbps 448 kbps
Line Attenuation 63.5 db 31.5 db
Noise Margin 2.8 db 13.0 db
 
Sorry for the delay..... i've been having a few BT issues......lol... its now week 12 of HELL !!!!!! should of been with UKONLINE 2 weeks ago!!!! I love Btw  :twisted:  ........ anyway ..... to bring you up to date..... 4th engineer visit (same CENSORED came as first two visit, drank my coffee and ermmm thats about IT ..... so i think enough is enough.... and ring to get my mac code... they agree that they have not kept their side of the contract ....... so i get my mac code  WOOOOOOOOOOOOO HOOOOOOOOOOO. I spend 1hr on phone to UKONLINE ... support UK based .... blah blah get an activation date of 9th august, told i will get FULL 8meg HA HA even quoting my line stats ...... but they agreed if i don't they will cap my line and revise billing !!!! thats sounds good ........... so anyway 2 days later BTw phone me .... they have actually sent someone out to see whats going on <SURPRISED LOOK> and they agree that my line stats are CRAP!!! and they have sent it to planning to see what happens!!!!! but the great BT way.... can't tell me what will happen or keep me informed!!!! good from a telecomunications company ???? don't you think......
 ..... anyway 9th comes and goes ..... NOWT so i ring UKonline ... BTw are holding it up !!!!! so they say they will chase BTw and ring me back !!!! .... before they do BTbroadband ring and say we've fixed your fault it was some cabling in the exchange!!!! and since then (still on BT with a new router i have brought as my BT2500V is locked to BT grrrrrrrrrrrrrr i have had a STABLE connection................... and with some delving on lowering snr levels<bt have stuck me @ 9db = 2304kbps> i've synched @ 3mbps well 3488kbps which gives you 3mbps for the last 4 days ...... <i got greedy and went for 3.5 mbps and lost sync DOOOHHHHH> so I HOPE THIS gives the 60+ club some hope on the ADSLmax front ....... I got a Netgear DG834N router and it holds sync down to like i've never seen before .... its gone to 0.9db and still held !!!!! so i'm looking forward to HOPEFULY 3mbs down and 768kbps up on UKONLINE with a 2quid a month saving !!!!!!! and NO bras profiling what you sync is what you get..... and when BTw finaly get round to re-running the cables hopefully 15mbps on UKONLINE adsl2+ <DREAMS>...................  anyway the main reason for this is to say......... DON'T LET BT fob you off !!!! and try several routers as the VARY HUGE AMOUNTS my Netgear DG834GT won't hold for more than 5 mins !!!!! and if you get a router you can tweak!!! you have MORE control of the situation.....anyway i hope this helps someone !!!!
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kitz

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Line Attenuation !!!
« Reply #9 on: August 14, 2006, 03:27:18 AM »

Thanks for letting us know the up to date situation... sounds like youve had a fun time (not) :/

By the looks of those stats you are only just about hanging on in there on those speeds.

If you wont have a bRAS to worry about with UKO should help, along with the fact you can setting your Target SNR on the router.

Hope the migration goes through ok and you get some decent speeds.  Let us know what happens :)
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soms

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Line Attenuation !!!
« Reply #10 on: August 15, 2006, 11:04:42 AM »

I spoke to a BT engineer doing some other work outside our place the other day and he thought that my stats should be fine for getting reliable ADSLmax service. He mentioned it is more error tollerent that traditional ADSL. I am also a bit more hopeful since my neighbour is on 1meg fixed and has same line attenuation and SNRM 9/14 or similar.
He also said that the stats were good for "living out here" which made me feel not so hard done by afterall, given my neighbour has samilar stats.  :wink:

(Stats (rounded) - line atten: 63/31 SNRM: 11-16/12-14)
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kitz

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Line Attenuation !!!
« Reply #11 on: August 15, 2006, 11:19:31 AM »

>>> He mentioned it is more error tollerent that traditional ADSL.

atm that may be up for debate - In theory it is meant to be because interleaving can be turned on... and you can run at the minimum SNR margin for your line.

However in the real world environment there have been a lot of people who have had an awful lot of problems with MAX - particularly those with the longer lines.

When BTw did all the max testing they tested on 2Mb lines.  Since max went live many ISPs helpdesks have been swamped with MAX problems. :(
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soms

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Line Attenuation !!!
« Reply #12 on: August 15, 2006, 01:10:56 PM »

Hmm, sounds a minefield indeed  :?

Its a difficult decision - stick to 512k fixed service on unknown ISP or go to BT Total BB on Max and perhaps get a 2meg service? Will stick 512k for now, but I am joining BT this year so maybe get little discount on some services  :wink:
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