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Author Topic: How can Line attenuation change?  (Read 805 times)

Sunzz

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How can Line attenuation change?
« on: December 07, 2016, 02:05:18 PM »

sorry if this is a stupid question, but for a long time i had a line attenuation of 21.1 / 17.6 , yet now it is 11.9 / 17.7 :S

isnt line attenuation based on the distance from the modem to the cabinet, so how can that change if the line length is the same? could it be line quality improvement or something?
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licquorice

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Re: How can Line attenuation change?
« Reply #1 on: December 07, 2016, 02:26:04 PM »

Line attenuation can only change if the physical charateristics of the line changes, e.g change of gauge of copper wire and it is only meaningful when expressed as a figure at a given frequency. However, you are not actually measuring attenuation, you are extrapolating it from power loss at various frequencies hence upstream and downstream attenuation figures are different. Different routers calculate this in different ways, and a change in tones used or a change of router can be perceived as a change in attenuation. Have any other parameters changed?
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Sunzz

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Re: How can Line attenuation change?
« Reply #2 on: December 07, 2016, 02:35:50 PM »

Line attenuation can only change if the physical charateristics of the line changes, e.g change of gauge of copper wire and it is only meaningful when expressed as a figure at a given frequency. However, you are not actually measuring attenuation, you are extrapolating it from power loss at various frequencies hence upstream and downstream attenuation figures are different. Different routers calculate this in different ways, and a change in tones used or a change of router can be perceived as a change in attenuation. Have any other parameters changed?

Yeh they have, i had a bt engineer here doing loads of tests but it couldnt figure out why my speeds so bad, also my stats were similar to the first image below even though that picture was from my plusnet router, then all of a sudden they stats changed to the second picture, this was wayyy after the engineer had gone :S the engineer told me basically crosstalk is slowing my speed and he even tried a different line or something like that.
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ejs

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Re: How can Line attenuation change?
« Reply #3 on: December 07, 2016, 02:40:35 PM »

Because Sunzz is on VDSL2, and their speed has decreased a lot recently, particularly the upstream, they've probably lost the use of one or more upstream bands. The attenuation for each band should remain much the same, but the aggregate figures will be different because they're no longer using one or more of the upstream bands.
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Sunzz

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Re: How can Line attenuation change?
« Reply #4 on: December 07, 2016, 02:42:05 PM »

Because Sunzz is on VDSL2, and their speed has decreased a lot recently, particularly the upstream, they've probably lost the use of one or more upstream bands. The attenuation for each band should remain much the same, but the aggregate figures will be different because they're no longer using one or more of the upstream bands.

Tbh i think i messed my speed up by restarting my router so many times, changing them and power cuts :(
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Weaver

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Re: How can Line attenuation change?
« Reply #5 on: December 15, 2016, 04:28:39 AM »

If you start using additional higher frequencies then this could change the weighting used by the modems in calculating the attenuation figure. High frequencies are attenuated more than lower ones. The calculation is some kind of average-like process combining the different figures obtained at all the various frequencies into one single result figure, so this combination calculation provides a likely answer.

A less likely possibility sometimes is that something physical about a line has changed, such as the use of thicker or thinner copper, or that a modem or its firmware has changed so that the analog front end is different, or perhaps the attenuation calculation software is different following a change of modem or a firmware update.

When some of my customers changed from BTW 0.5 Mbps ADSL to approx 7 Mbps downstream ADSL "Max" service back in 2006, their reported attenuation figures changed a lot. This was due to the calculation including additional, previously unused higher tones.
« Last Edit: December 15, 2016, 05:08:29 PM by burakkucat »
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