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Author Topic: Effect of low SNR (Max adsl)  (Read 16511 times)

canon

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Effect of low SNR (Max adsl)
« on: October 19, 2006, 02:43:19 PM »

Hi, my first post - I thought I would get some good information here as the web site is very informative.
I was activated on Max ADSL (Metronet) jus 9 days ago. My Netgear DG834 sync's at 8128, sometimes a bit lower at night but I'm re-powering in the mornings now so always get 8128.
However, in the evening my Noise Margin drops from 8 db down to 3 db or less - the DG834 still synch's ok.
the BT test says I'm set at 6500 kbps at present, best d/l speeds are about 5000 kbps, dropping to about 1400 kbps in the evening.
I have connected to the master socket in the day, it did not make any difference to the Noise Margin but I wlll try it in the evening too.

My question is - is the low evening Noise Margin likely to have much effect on speed both actual and the BT configured speed? Can BT improve the Noise Margin at their end?
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kitz

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Re: Effect of low SNR (Max adsl)
« Reply #1 on: October 19, 2006, 05:11:03 PM »

Hi and welcome :)

Quote
>> My Netgear DG834 sync's at 8128, sometimes a bit lower at night
>> the BT test says I'm set at 6500 kbps at present

The 6500 profile is based on your lowest sync speed, therefore that implies that at some point your router has synced anywhere in the  7392 - 7936 kbps region

Quote
>> best d/l speeds are about 5000 kbps, dropping to about 1400 kbps

Sounds possible Im afraid..  evenings are when adsl experiences the most contention because more people are online and using it. 
Ive been through phrases of bad contention myself several times in the past - in fact its probably the reason why I first became so interested in finding out how adsl worked.
Believe it or not, but BTw define anything over 400kbps as acceptable for a home connection because IPStream adsl is a shared resource.
When I first got "maxed" I was seeing speeds in the region of 6-7Mb, since then my speeds have gradually reduced as more users are maxed - in fact at the weekends I was seeing speeds under 1Mb and there was nothing I could do.  Aside from the fact that Id carried out BTw speed tests and knew that it wasnt my ISP.

However there is some light at the end of the tunnel, my exchange was evenutally marked "red" a few weeks ago..  and since Monday Ive been getting good speeds again - so BT has hopefully put more bandwidth on the backhaul.

Theres more information about Acceptable Speeds.

Quote
>> it did not make any difference to the Noise Margin but I wlll try it in the evening too

Evenings is when your SNR Margin is most likely to drop for various reasons.. when your SNR Margin is lowest then thats obviously when you will sync at the lower speeds.

Quote
>> is the low evening Noise Margin likely to have much effect on speed both actual and the BT configured speed?

Yes it will affect your sync speed, if theres insufficient Margin, then you get a lower sync speed.
Secondly, when the SNR is lowest, its when you are the most likely to get lost packets... therefore your router has to re-request this data, which makes actual throughput slower.
Im not sure if the later is true in your case, but if your router shows lots of  CRC/HEC errors then it will be a contributing factor to slower actual throughput speed.

Quote
>> Can BT improve the Noise Margin at their end?

Not really* - Noise margin is how well your router and the dslam at the exchange can *hear* each other.  If youre on a long line, then there isnt really much anyone can do about that.  The further away from the exchange you live then your signal weakens.
There are a few things that you can perhaps try and do to improve SNR Margin on your side.  Theres some tips to help try and improve low SNR here.

*Unless there is an actual fault on your line, such as worn line

If you want to provide your line stats (sync speed, SNR Margin and Attenuation), then someone can perhaps look at that and see if things look normal.
Unfort Im not going to be around for the next few days..  but one of the other guys should hopefully pick up on them.
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canon

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Re: Effect of low SNR (Max adsl)
« Reply #2 on: October 20, 2006, 08:34:41 PM »

Kitz,Thanks for the interesting reply.
To anwer some of your questions and some more of mine.

quote: implies that at some point your router has synced anywhere in the  7392 - 7936 kbps region.
Yes that is correct, after I re-powered the router during th evenings (as recommended ny Metronet  to help the 'learning' process). Since then I've only done that in the day and kept the full 8128kbps sync speed.

quote: if your router shows lots of  CRC/HEC errors then it will be a contributing factor to slower actual throughput speed.
I wasn't sure how to check this but from following your instructions on the Stats page for the DG834, I did the BusyBox thing and could see some numbers in the interleaving ('on' btw) section for CRC, they went from 1 (soon after power on) to 159 in 3 hours.
Is this good or bad? There were no HEC errors.

quote: provide your line stats (sync speed, SNR Margin and Attenuation), then someone can perhaps look at that and see if things look normal
Here are my stats: -
DOWN - sync 8128 kbps, atten 36 db, Noise Margin 8 db. The latter figure drops to 3 db or less in the evening, zero somtimes but sync is held no probs.
UP - sync 448 kbps, atten 10.5 db, Noise Margin 24 db. Evening figures remain the same.
The BT test dial says I'm 2.4 km from the exchange.

I've now connected my router directly to the BT master socket with a long ethernet cable to my PC. It's had little effect on the daytime stats but the evening DOWN Noise Margin has gone up to 8 db, sometimes 6 db. D/L speeds are better too - but it's Friday and everyone is down the pub maybe.

Does this look as though I should re-wire my ADSL extension, with a filterd line box and CAT 5 extension cable?
I had hoped to get away with not doing this, especially your 'Experience/Reality' page shows a similar situation with the same router and yet getting decent actual speeds (better than mine, although I'm not through the 10-day initial period yet).
Would re-wiring make much real difference, bearing in mind that I would still have the same length extension (~ 15M)?
It does look as though the evening noise is very local, can't think what though.

Sorry for all the rambling but I want to get the best possible - I'm like that!
Thanks.
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soms

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Re: Effect of low SNR (Max adsl)
« Reply #3 on: October 20, 2006, 11:44:35 PM »

I am a great believer in extension wiring being detromental to the quality of user ADSL signal/service. Unfortunately, typical telephone cable isn't very highly twisted which can lead to signal loss and because it is also unshielded electrical interference from appliances, cables etc can also interupt the ADSL.

A BT DSL face plate filter for the NTE5A master socket is highly recommended, particuarly if you have runs of regular telephone extension cable from the master socket.

Cat5e cable could give you an improvement, because it is highly twisted, better maintaining signal integrity; however most cat5e is UTP, which by definition is unshielded, leaving the cable vulnerable to some types of interference as with regular telephone cable.

Personally I am using a modified BT DSL faceplate filter (from clarity.it) using shieleded category 5e cable for my ADSL extension (master socket is in the roof space).

It has helped me at least and I can be sure that the wiring delivering the ADSL within the home is rock solid and as good as possible which helps narrow down the list of problems when there is a problem with the service.

Hope that helps a bit.

*EDIT*

To clarify, my ADSL extension socket uses a single pair of wires (in a run of shielded cat5e) from the unfiltered outputs on the BT DSL faceplate splitter to a dedicated phone socket into which I have plugged in a BT MF50 microfilter and then the ADSL modem using a line cord.

From the microfilter I am using a belkin shielded high speed internet cable (RJ-11 to RJ-11) which also helps ensure maximum signal quality from the socket/microfilter to the router/modem.

Also avoid have the ring wire connected to your wiring where possible. It can introduce interference onto the main speech pair and is unecessary, as both plug in microfilters tend to contain ring capacitors (just like in the master socket) and also most modern telephones seem to just use 2 wires and have their own ring capacitor built in.
« Last Edit: October 20, 2006, 11:51:58 PM by soms »
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roseway

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Re: Effect of low SNR (Max adsl)
« Reply #4 on: October 21, 2006, 07:48:05 AM »

Yes, soms has it right. A filtered master socket faceplate is the best technical option. If you can't put the router nearby, then you need good quality Cat5e cable from the unfiltered terminals on the faceplate to where the router is. Shielded cable would be best of all, but (in my opinion) it may not make a lot of difference.

With a filtered faceplate it shouldn't matter whether you leave the ring wire connected or remove it, because it's on the filtered side and therefore shouldn't interfere with the ADSL. It's probably best to leave it connected, just in case you have a phone that needs it (one of mine does, to my surprise). However, if you're not using a filtered faceplate then disconnecting the ring wire can be very worthwhile, and the plug-in filters provide the ring connection for phones that need it.

Eric
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canon

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Re: Effect of low SNR (Max adsl)
« Reply #5 on: October 21, 2006, 10:19:30 AM »

Thanks for the info & advice guys.
Soms - where did you buy your shielded cable, was it network cable rather than CAT5 telephone extension cable?
I want to order some kit in the next few days, probably from Clarity but they don't seem to supply shielded cable.

A practical query - I need to re-do 2 spur extensions from the master socket (upstairs with ADSL & down). Currently I have 2 wires in an IDC slot to achieve this -  is this ok?
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soms

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Re: Effect of low SNR (Max adsl)
« Reply #6 on: October 21, 2006, 10:37:18 AM »

I bought a reel of cable from screwfix direct, but they no longer seem to stock it!

No doubt it is available just the same else where, and yes, it was network grade cable (slightly thicker wires).

It was sold as Foil Shielded (FTP) cable.

For your existing spurs, both extensions only need terminals 2 and 5 connected back the master socket. This is normally the blue pair where it is available. You do not need to connect the ring wire, because as mentioned above, both microfilters and telephones themselves now seem to generate their own ring signal.
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canon

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Re: Effect of low SNR (Max adsl)
« Reply #7 on: October 23, 2006, 09:16:18 AM »

I've now ordered kit to re-wire my extensions, Filtered faceplate, CAT 5 cable etc. Couldn't get shielded cable but may use foil tape as cable will be in conduit or trunking for most of the way. Should get an improvement, some of existing cable is not twisted pair & some runs alongside a main cable - I'll move position when I re-wire.
For those interested, attached is pdf graph of my stats since Max activation, note the difference when connected to master socket. I've just learnt that my exchange is status VP Red so that may be having an effect on D/L speeds.
The kinks in the Sync speed are when I re-connected in the evening and got a drop in value. I have only re-connected in day time recently and will leave connected from now on.

[attachment deleted by admin]
« Last Edit: October 23, 2006, 09:20:28 AM by canon »
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canon

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Re: Effect of low SNR (Max adsl)
« Reply #8 on: October 27, 2006, 11:45:44 PM »

 :) I think I've cracked It!
Finished installation of new extension wiring today and Noise Margins are the same as when connected into Master Socket.
I used CAT5e 3 pair cable and used one pair for the ADSL signal hard wired into the new filtered face plate adaptor - not a separate cable for ADSL! I have an extension that goes to the upstairs (15M via a slightly complicated route), the one I connect to is at the end but there is an intermediate socket in another room in series.
The new sockets are both dual Phone/RJ45; the ADSL pair "pass through" the intermediate IDC connectors without a break.
I bought a proper IDC tool from www.clarity.it with all the other bits and pieces. It cost me about ?70 but looks like it was worth it!

I've monitored the noise margins all day and they are the same as from the master socket: - DOWNstream NM 9db daytime, 6db evening at worst (8db at the mo); Atten 36db, sync 8128kbps always. UPstream NM 25db (a little up from before), Atten 10db, sync 448kbps.

Just thought I'd share this info' - might help someone else.
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roseway

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Re: Effect of low SNR (Max adsl)
« Reply #9 on: October 28, 2006, 11:36:37 AM »

Quote
I bought a proper IDC tool from www.clarity.it with all the other bits and pieces. It cost me about ?70 but looks like it was worth it!

That sounds like a serious tool! Are you planning on going into business doing telephone and data wiring?

I'm afraid I'm a bit of a cheapskate and I got the cheaper 'imitation Krone' tool.

Eric
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canon

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Re: Effect of low SNR (Max adsl)
« Reply #10 on: October 28, 2006, 07:34:38 PM »

 :no: Sorry if I mislead you, I bought the Krone copy tool too, it's ok once you know what all the bits/settings on it do. I did find some instructions on the web but not at Clarity.
I'm retired,   :sleep: I only work for myself!
« Last Edit: October 28, 2006, 07:36:11 PM by canon »
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EVIL-SCOTSMAN

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Re: Effect of low SNR (Max adsl)
« Reply #11 on: October 28, 2006, 09:20:15 PM »

Check this out, my buddy in the netherlands, he connected a ferrite block to the cable that immediatly comes out of the phone socket and he said he has got a better sync speed and also a faster download speed.

The ferrite blocks are on everything nowadays and are for interferance, monitors have them, basically everything has them nowadays.

He says it has helped him a great deal, so maybe its worth a try to a few ppl here ?
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canon

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Re: Effect of low SNR (Max adsl)
« Reply #12 on: October 28, 2006, 09:42:49 PM »

connected a ferrite block to the cable that immediatly comes out of the phone socket

Any details, picture, how connected etc?

The one on my scanner USB 2 cable seems to clamp on the outside. Time for a Google search, Maplins or an electronics engineer! Could  be be a quick fix for a a lot of people.
However, my Noise Margins are now the same as from a direct connection to the master socket so any low values are a result of upstream problems out of my control. No probs sync'ing at max values either.
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EVIL-SCOTSMAN

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Re: Effect of low SNR (Max adsl)
« Reply #13 on: October 28, 2006, 10:32:48 PM »

No I havent go any pics or any more details, but I could get them on say monday/tuesday as he is away for the weekend, all he did say to me was he put a ferrite block on  the cable right next to the wall socket and his sync speed and also download speed increased due to it, but remember this is the netherlands and although he is also on radsl-20mbit download  the system is slightly different over there regarding bras profiles and such, so it may not work as good over here as it has with him ???? i really cant say, but he is a network engineer and knows his stuff so I wouldnt expect him to be speakin BS...
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canon

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Re: Effect of low SNR (Max adsl)
« Reply #14 on: October 28, 2006, 10:53:24 PM »

I await some more info with interest. I've Googled the subject and Maplin & others sell clamp on ferrite rings "to reduce interference on ..... and telephone lines". My nearest Maplins has 1 in stock of the correct size! I'll try to get there next week but still interesed in your mate's info'. Ta.
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