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Anonymous
(Unregistered)Fri 01-Apr-11 18:33:36
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Slow Sync Speed Question


[link to this post]
 
Just learning in to this please be gentle! Trying to help out a friend here...

Given the following downlink stats the ADSL line capability estimator (from FAQ) says that the following line should support a min of 2Kbps sync on ADSL or about 5.5Mbps on ADSL2+:

378 kbps - Sync
50 db - Attenuation
25 db - Noise Margin

ISP is Sky broadband, presumably ADSL2.

I noticed two things
1) The user turns off the modem when not in use.
2) There was an unfiltered extension socket wired straight into the master socket. I am not sure this is an NTE5 master, and I ran out of time to check it.

I put a filer on the extension (the phone line is quieter now:))

Q1. So why is the sync speed so slow? My limited understanding of the stats are that that low attenuation is good (50dB seems OK to me) and a high noise margin is good (am I wrong?).

Assuming this line should get a faster speed:
Q.2. How do I get the synch speed back up? I rebooted the modem. No change. Tried unplugging all phones. No change
- Is there something the ISP can do to limit synch speed, or is this dynamic and instant
- should I now be looking at the internal house wiring (modem is direct to the master socket. Its that wired in extension that worries me).

Lastly sorry if you read the above on other forums today. Trying to get this resolved ASAP as back to work next week = no time to 'play'.

TIA, Batch
Standard User Zarjaz
(knowledge is power) Fri 01-Apr-11 19:07:59
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Re: Slow Sync Speed Question


[re: Anonymous] [link to this post]
 
You'll need to supply a little more info I'm afraid. The full stats from the router, hopefully a 'where it is' and then 'at the NTE test socket, nothing else connected'.

1. So why is the sync speed so slow? My limited understanding of the stats are that that low attenuation is good (50dB seems OK to me) and a high noise margin is good (am I wrong?).

No, 50db is fairly high for attenuation, and on a variable speed service, low snr is good, around 6db, roughly.

Is there something the ISP can do to limit synch speed,

Yes, depends if this is Sky LLU, or Sky reselling BT wholesale, but both can be capped, but the stats will hopefully show whats what.

Anonymous
(Unregistered)Fri 01-Apr-11 19:21:24
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Re: Slow Sync Speed Question


[re: Zarjaz] [link to this post]
 
Thank you for your reply.

Excuse my ignorance, but which further stats would your require?

It may take a while to get this information - a week or two due to work, etc. So I would be grateful if you could give me a few pointers as to what to look out for - if that's possible.

I am confident this is Sky LLU since they are on the same exchange as me (Blunsdon) .

Is it possible DLM is raising the target SNR Margin and will eventually right itself if the line is stable (e.g. if the previously unfiltered phone is now filtered)? Or have I got the wrong end of the stick?

Thanks again. Batch


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Administrator MrSaffron
(staff) Fri 01-Apr-11 20:01:25
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Re: Slow Sync Speed Question


[re: Anonymous] [link to this post]
 
Seeing the upstream figures at the same time can help spot oddities.

378 kbps - Sync
50 db - Attenuation
25 db - Noise Margin

The high noise margin suggests one of two things:

1. The line was very noisy last time modem connected, so a power off/on might give a better sync now.
2. If the sync is always 378Kbps and this is a Sky LLU service, probably they have put the user on a fixed speed profile, and you need to enquire about getting them to reset the DLM.

Sky doesn't have the same dynamic target margin as BT Wholesale, hence question about which product, which if person doesn't know can be inferred from upstream speed.

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Anonymous
(Unregistered)Fri 01-Apr-11 20:16:20
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Re: Slow Sync Speed Question


[re: MrSaffron] [link to this post]
 
Thanks again.

Stats DL and UL were:

378 kbps 764 kbps
50 db 33 db
25 db 9 db

I reset the router after filtering the unfiltered phone - same speed.

If there is nothing in the above stats, and nothing has improved overnight I'll help them to email sky requesting them to reset the DLM.

Really appreciate this help by the way,

Batch
Standard User Zarjaz
(knowledge is power) Fri 01-Apr-11 20:36:04
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Re: Slow Sync Speed Question


[re: Anonymous] [link to this post]
 
Thats what Mr.S was trying to tell you if it is Sky LLU service, there is no DLM.

Those are 'odd' sync rates. But if I had to put my money anywhere*, I'd say it's Sky's own kit, and they have capped the D/S sync rate to gain stability. You can ask them to adjust this, but there is really no point until you know it was done in the first place..... I suppose it might just have been in response to the unfiltered phone. Out of interest, have you checked all the Sky boxes are filtered also ? They set it up wrong once, who know's they might have done it wrong twice.



* My hunch being based on the high downstream SNR, on a shorter line might well show 30db as evidence of the cap.

Anonymous
(Unregistered)Fri 01-Apr-11 20:51:12
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Re: Slow Sync Speed Question


[re: Zarjaz] [link to this post]
 
Right, thanks!

As far as I can see there is only the master socket (traced from cable from telegraph pole into house) and this wired in to the master socket extension. Both now have filters.

I replaced all filters and the ADSL RJ11 cable with known good. The Sky box is on one of these filters, the house phone on the other. So I am fairly sure everything is now covered.

I understand there is no point in trying to increase the sync speed if the underlying problem has not been fixed. not sure how to prove it one way or the other...

Thanks again.

Batch
Anonymous
(Unregistered)Fri 01-Apr-11 20:56:00
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Re: Slow Sync Speed Question


[re: Anonymous] [link to this post]
 
In reply to a post by Anonymous:
As far as I can see there is only the master socket (traced from cable from telegraph pole into house) and this wired in to the master socket extension. Both now have filters.


that should read:

As far as I can see all now have filters on. There is the master socket (traced the cable from telegraph pole into house and the master is the first and only box attached to it) which has a filter, and there is this "wired in to the master socket" extension which also has a filter now (previously didn't).
Standard User Zarjaz
(knowledge is power) Fri 01-Apr-11 21:15:51
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Re: Slow Sync Speed Question


[re: Anonymous] [link to this post]
 
OK, just one more thing to try, does the "master socket (traced the cable from telegraph pole into house and the master is the first and only box attached to it" have a detachable lower potion, if so, removing this and plugging the router directly into the now exposed test socket, should be all thats needed to prove it's not 'your' fault.

Anonymous
(Unregistered)Fri 01-Apr-11 21:47:53
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Re: Slow Sync Speed Question


[re: Zarjaz] [link to this post]
 
I need to double check to see if it does have a test socket under the faceplate.

From memory it wasn't like mine, I think the "detachable" bit was more like a letter box/window in the socket than a whole removable bottom section (I guess that may not make sense). Memory might be paying tricks mind.

Will try having a look next time I'm there.
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