Line Attenuation 96dB - how is this possible?!

Forums › New Zealand Broadband › Line Attenuation 96dB - how is this possible?!

Attobrute

19 posts

Geek

#29447 7-Jan-2009 12:53

I live in Auckland, in the area of Telecom's Onehunga exchange. I have one of the original Xtra "Go Large" accounts - supposedly as fast as possible in both directions.

Results from a speed test done soon after we got ADSL:

Download 1412 kb/s
Upload 128 kb/s

Recently my ADSL connection speeds appear to be getting slower. I also visited my brother-in-law's house, and their ADSL is 3-4x faster than ours (subjectively).

Following advice in these forums I contacted Telecom, and asked them to perform a line check. These are the results I received:

Here are the test results you requested earlier
Your distance from the exchange is approximately 3.9kms

Cable Length: 3,910.9m (to locale: ON)
Copper Attenuation: 96 dB (to locale: ON)
Loop Resistance: 825.7 Ohms (to locale: ON)

Thank you for your inquiry

According to the attenuation result I should have a very poor ADSL connection indeed, but even though it is bad, it is not that bad!

Is this result somehow inaccurate?

The reason I am performing these investigations is that I am thinking of changing ISPs to someone else like Orcon for example, who apparently offer ADSL2+. If I get this will I notice any speed improvement, given the distance our house is from the exchange?

Cheers!

RalphFromSnap

776 posts

Ultimate Geek

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Snap Internet

#188007 7-Jan-2009 13:44

Thats probably the loop attenuation, not single direction attenuation (much more relevant in adsl).

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Spyware

3764 posts

Uber Geek

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#188010 7-Jan-2009 13:48

Maybe attenuation figure depends on frequency used. ADSL figure relates to 300 kHz.

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STI

239 posts

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#188015 7-Jan-2009 14:09

As Spyware pointed out the attenuation depends on frequency it's measured at. What is the attenuation figure displayed on your modem configuration page? I was quoted 85dB by Telecom when I first got broadband, while actual modem downstream attenuation was ~40dB.

garvani

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#188030 7-Jan-2009 15:22

First of all Go Large isnt as fast as your line can go in both directions, upstream is capped at 128k (possibly 192 cant quite remember) and because of this and the way Adsl works your downstream will automaticaly be capped at 3.5mbit.

I have had problems with high Attenuation in the past, we rewired from the demarcation point to the jack and it decreased it somewhat, its now 69 Upstream and 52 Downstream, and i synch at 2281 Kbps.. It used to synch at ~400Kbps and be somewhere in the high 80's! So this is a vast improvement.

Attobrute

19 posts

Geek

#188046 7-Jan-2009 17:24

This is the best I can achieve now...

alexx

867 posts

Ultimate Geek

#188055 7-Jan-2009 18:11

Have you checked if you are in an area to be moved onto a cabinet (one with a DSLAM in it)?
Check by entering your address here:

http://www.telecomwholesale.co.nz/maps

If you are and it's going to happen soon, then you might be best to stay with Xtra.

In garvaini's post he mentioned rewiring... check this thread for more on ADSL connections speeds (if you haven't checked already).

http://www.geekzone.co.nz/forums.asp?ForumId=49&TopicId=27834

If the limitation is in your house wiring or the Telecom cable back to the exchange, changing ISP probably won't help.

jfnz

211 posts

Master Geek

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#188096 7-Jan-2009 20:53

Have a read of this thread.

If it's still worse than expected email adsl_helpdesk@telecom.co.nz with the ADSL line number, your Telecom account number and a description of the issue along with troubleshooting already performed.

As Alexx suggested, check here for information regarding the availability of ADSL2+ and projected cabinet installation dates.

Also, GoLarge is shaped aggresively which results in poor performance. Once your connect rates are sorted you'd fare better on a newer ADSL2+ plan as they're not at all restricted.

Please note: Any posts, comments, or contributions in this forum are posted by me as an individual acting in my own right and do not necessarily reflect the views of any company I work for, clients I've consulted for, or anyone else.

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honem

194 posts

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#188441 9-Jan-2009 19:02

Just a note here about the results you got back

They don't measure them.

These are expected results.

Basically (at least last time I checked) they put your address into a spreadsheet that calculates it for you.

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jfnz

211 posts

Master Geek

Trusted

#188444 9-Jan-2009 19:09

Yeah, it's a calculated value as opposed to a direct test result.
That said if the records are out of date (e.g. you've just moved or had some changes made to your exchange) the results may be inaccurate.

96dB is high, however it isn't an astounding figure. I've seen ADSL functioning (albeit not extremely fast) at 115dB on those line tests.
As for resistance it should be relatively reliable if the number returned is <1000ohms

alexx

867 posts

Ultimate Geek

#188473 9-Jan-2009 21:21

Even if 96db was the measured value at some frequency, it might be possible to have reasonable line performance at other frequencies and a working ADSL connection due to the Discrete Multi-Tone (DMT) modulation scheme used.

http://en.wikipedia.org/wiki/ITU_G.992.1

Attobrute

19 posts

Geek

#188978 12-Jan-2009 13:57

Here is another thread related to this one...