Line attenuation at 85dB?

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STI

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#19225 10-Feb-2008 15:48

I'm finally planning to get broadband (Xnet fusion) to our house (09 827, New Lynn exchange), so I called up Telecom on 123 to find out the distance from the local exchange. No one could actually tell me the distance, but one representative told the line attenuation is 85dB (He couldn’t confirm which frequency this attenuation figure is measured at).

From my understanding line attenuation is directly related to the distance from the exchange, and after doing some research this translate to about 6K+ distance and can expect speeds below 2Mbps.

So my question; Is it worth getting Xnet fusion with full speed up and down? Or should I settle for a cheaper 2Mbps plan?

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#109668 10-Feb-2008 16:16

STI: ...one representative told the line attenuation is 85dB (He couldn’t confirm which frequency this attenuation figure is measured at).

So my question; Is it worth getting Xnet fusion with full speed up and down? Or should I settle for a cheaper 2Mbps plan?

If your Line Attenuation is really 85dB, you will be lucky to get any sort of broadband connection over your phone line.

Hopefully they have made a mistake

I find it hard to believe that you are 6km+ from an exchange in any part of New Lynn. I know the area pretty well, and it is bordered on one side by Avondale, then by Blockhouse Bay, then by Titirangi then by Kelston, then by Glen Eden, all of which have their own exchanges AFAIK.

So, I think it's pretty unlikely that you are really 6km+ from the exchange!

cyril7

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#109673 10-Feb-2008 16:26

I assume they use some other method based on cable plans to estimate the line attenuation, as without a ADSL modem (or test kit) on the line to perform the measurement how do they measure it. If you line is currently not provisioned to the DSLAM then my guess is 85dB of loss between MDF's is a bit optimistic.

Cyril

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#109692 10-Feb-2008 17:25

Start with 2mb plan, check actual line specs, and upgrade your plan later if you can get full speed, 2mb

isn't slow anyway, and make sure you get a good modem that can handle it....

just my 2c

STI

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#109700 10-Feb-2008 17:48

grant_k:
If your Line Attenuation is really 85dB, you will be lucky to get any sort of broadband connection over your phone line.

Hopefully they have made a mistake

I find it hard to believe that you are 6km+ from an exchange in any part of New Lynn. I know the area pretty well, and it is bordered on one side by Avondale, then by Blockhouse Bay, then by Titirangi then by Kelston, then by Glen Eden, all of which have their own exchanges AFAIK.

So, I think it's pretty unlikely that you are really 6km+ from the exchange!

I had a look at Google maps and our house can't be more than 3km approximately from any of the local exchanges you mentioned. So as you say 6km is quite unlikely. Then again our house is built in the 1950 era and those old copper wires probably contribute to the line attenuation as well.

Is there anyway to measure the line attenuation accurately before I go ahead with broadband? Also 85dB may be only for telephone voice signals, i.e. in the 300-3kHz range. As broadband signals operate at a higher frequency the attenuation characteristic of the copper wire maybe different?

If the figure of 85dB is accurate and can I get a Telecom service person to have a look at it under faults service?

grant_k

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#109702 10-Feb-2008 17:56

STI: ...85dB may be only for telephone voice signals, i.e. in the 300-3kHz range. As broadband signals operate at a higher frequency the attenuation characteristic of the copper wire maybe different?

Attenuation at broadband frequencies is much Higher than at voice frequencies, not the other way around. If there was 85dB attenuation on Voice Signals, you would never hear anything at the other end

Have you used the Xnet Line Checker to see what it says about your line?

http://www.xnet.co.nz/hsi/linecheck.shtml

Niel

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#109703 10-Feb-2008 18:06

I would ask the neighbours how their broadband is. That is probably the best way to find out. That said, after 7 years we still have not made friends with our neighbours...

You should be safe in your area. I think the 85dB might be the limit of what their software can measure, and not a real measurement. It might even have picked up a signal from a neighbouring line if you have never had ADSL on the line.

We are in Edgewater Pakuranga about 3.5km from the exchange and get 7Mbps with XNet. We are now on FS/FS. Before we were on FS/128k and would get 3.5Mbps (the up speed limits the down speed by being slow to return acknowledge packets). My line attenuation is 38dB.

With XNet you can start with one plan and any time switch to another. They will charge you for the number of days spent on each plan. They will probably be grumpy if you change 5 times in one month, but one or two times should be OK especially when they also can see there is a problem with the line. And XNet will sort out any line problems with Telecom, you do not need to get involved at all other than logging a fault with XNet. I suggest you start off with FS/FS to see what speed you can get and then decide if you should go slower, or start off with 512k/128k or FS/128k and check your modem what the sync speed is to see if it is worth to go to FS/FS or drop to 512k/128k. The modem sync speed is about 10% higher than what your FS speed will be.

(There is a referral programme, would appreciate it if you PM me for my details to give to XNet. Either way, I enjoy promoting XNet.)

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Niel

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#109706 10-Feb-2008 18:12

Note your exchange is about to be upgraded to ADSL2+ which means that you will get unstable internet (lots of disconnections) until hte last day of the commissioning period. See here: http://www.telecom.co.nz/binarys/adsl2%20080131.pdf

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STI

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#109709 10-Feb-2008 18:23

grant_k:
Attenuation at broadband frequencies is much Higher than at voice frequencies, not the other way around. If there was 85dB attenuation on Voice Signals, you would never hear anything at the other end

Have you used the Xnet Line Checker to see what it says about your line?

http://www.xnet.co.nz/hsi/linecheck.shtml

According to broadband line check:

UBS (Unbundled Bitstream Service) is available in the exchange area servicing the premesis for the line number requested

The estimated downstream linerate for this query is < 2Mbit/s

Occasionally, there are factors such as distance from Telecom's equipment which may mean that Xnet HSI is unable to be delivered to a particular site or address.

Do they calculate the downstream linerate using the line attenuation figure? I guess ADSL 2+ service isn't available in New Lynn exchange yet.

grant_k

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#109712 10-Feb-2008 18:41

STI: Do they calculate the downstream linerate using the line attenuation figure? I guess ADSL 2+ service isn't available in New Lynn exchange yet.

As Cyril said earlier, it's not really possible to calculate the Line Speed without having ADSL connected, so they are probably just estimating it, using Line Length as a guide.

Given that they have said < 2 Mbps I would not expect that you will get any benefit from ADSL2+.

Also, Niel has mentioned repeatedly that he suffered from disconnections and speed variations when his exchange was upgraded. We are on the Blockhouse Bay exchange and never experienced any disruption at all when that was upgraded during December.

STI

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#109714 10-Feb-2008 18:44

Niel: I would ask the neighbours how their broadband is. That is probably the best way to find out. That said, after 7 years we still have not made friends with our neighbours...

I know what you mean. Anyway if I ask about broadband from my neigbours answer most likey going to be "what's broadband?"

Niel:You should be safe in your area. I think the 85dB might be the limit of what their software can measure, and not a real measurement. It might even have picked up a signal from a neighbouring line if you have never had ADSL on the line.

According to the customer rep I was talking to line attenuation can range from 10-125dBs. At the higher end broadband isn't available. If the downstream estimate of 2Mbps is accurate (can a estimate be accurate?) 85dB sounds about right.

Niel:We are in Edgewater Pakuranga about 3.5km from the exchange and get 7Mbps with XNet. We are now on FS/FS. Before we were on FS/128k and would get 3.5Mbps (the up speed limits the down speed by being slow to return acknowledge packets). My line attenuation is 38dB.

With XNet you can start with one plan and any time switch to another. They will charge you for the number of days spent on each plan. They will probably be grumpy if you change 5 times in one month, but one or two times should be OK especially when they also can see there is a problem with the line. And XNet will sort out any line problems with Telecom, you do not need to get involved at all other than logging a fault with XNet. I suggest you start off with FS/FS to see what speed you can get and then decide if you should go slower, or start off with 512k/128k or FS/128k and check your modem what the sync speed is to see if it is worth to go to FS/FS or drop to 512k/128k. The modem sync speed is about 10% higher than what your FS speed will be.

I will try the FS/FS with Xnet, then will downgrade if I get slow speeds. Is there anything I can do from my side to improve line attenuation, like rewiring the house? Can I expect faster speeds when the ADSL 2+ connections are enabled?

cyril7

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#109733 10-Feb-2008 19:42

Line length is roughly 13.8xattenuation, therefore 4.5km which is normally concidered the cutoff where the line becomes to slow and unpredicable is around 55dB.

Cyril

grant_k

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#109736 10-Feb-2008 19:52

STI: Is there anything I can do from my side to improve line attenuation, like rewiring the house?

Possibly, but it would pay to wait and see if you can actually get broadband first.

STI: Can I expect faster speeds when the ADSL 2+ connections are enabled?

Given that Telecom have said < 2 Mbps expected line speed, I would not expect that you will get any benefit from ADSL2+.

manhinli

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#109745 10-Feb-2008 20:20

This easier to understand chart makes it easy to understand why 85dB ain't going to be helped much better by ADSL2+...

You might not be able to get broadband at all...

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Niel

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#109748 10-Feb-2008 20:41

grant_k: Also, Niel has mentioned repeatedly that he suffered from disconnections and speed variations when his exchange was upgraded. We are on the Blockhouse Bay exchange and never experienced any disruption at all when that was upgraded during December.

Pakuranga was the second exchange that was upgraded to ADSL2+. It is possible that since then Telecom has a better grip on the settings and switch over might be smoother now.

Also, the amount of commissioning required depends on how similar (or different) the cables are at the exchange. If everything is underground, then all settings should be similar. If some are overhead, then those lines will need individual tuning due to highly varying conditions.

It was not a problem with my modem or wiring or external interference. And the problem went away exactly on the last day of commissioning and in 8 months never returned.

Wikipedia suggests that the line attenuation scale ends at 90 dB with 0: http://en.wikipedia.org/wiki/G.DMT
It looks like 85dB is 512k on ADSL2+ and may be the end of the "possible" scale. To put it in perspective, 85dB loss means if you put 1V in at one end then you get only 0.000 000 003V (3nV) out at the other end. That is a massive loss. I suspect the Telecom person did a test of your line but the test picked up a signal from a neighbouring line or perhaps there is moisture in your wiring or something.

It will cost you nothing to sign up with XNet and there is no contract, so try that and see what you get. Getting a reading off your modem is more reliable that asking someone over the phone what they think.

Note that I have always had good speed with XNet, except this last week there has been reports of slow international speed while national speed is still very fast. I believe they are sorting out configuration issues on their new servers and at the same time getting swamped with Fusion uptake.

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xlinknz

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#109845 11-Feb-2008 13:03

Niel:
We are in Edgewater Pakuranga about 3.5km from the exchange and get 7Mbps with XNet. We are now on FS/FS. Before we were on FS/128k and would get 3.5Mbps (the up speed limits the down speed by being slow to return acknowledge packets). My line attenuation is 38dB

Are you telling me I have to upgrade my plan from FS/128 to FS/FS to improve my download speed on adsl2+

I would be very disappointed to find out that to benefit from adsl2+ I need to spend more money with my ISP ?

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