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Author Topic: Losing 6db and 20Mb, gaining 6db get 20Mb back?  (Read 1874 times)

ktz392837

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Losing 6db and 20Mb, gaining 6db get 20Mb back?
« on: April 07, 2015, 10:05:39 PM »

My line is alternating between 80 and 60Mb.  My db will drop to 1db it will hold on to the connection for ages but eventually it resyncs and lobs 20mb off my speed.  After a few days I notice my db is 12 so I resync to get my 80Mb back.

Is this crosstalk and someone is switching their modem on/off or similar?

Thanks
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kitz

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Re: Losing 6db and 20Mb, gaining 6db get 20Mb back?
« Reply #1 on: April 07, 2015, 10:34:49 PM »

Possible, but it could also be the DLM cutting in and out which will knock off some speed if it applies error correction and interleaving.
Its hard to say without inspecting your line stats.

I wouldnt ever let it get down to as low as 1dB even if its hanging in there, because errors will be produced.    3dB is needed to load a single bit into the bins, so dont let it get below that.   Its error count that can cause the DLM to eventually intervene.
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boost

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Re: Losing 6db and 20Mb, gaining 6db get 20Mb back?
« Reply #2 on: April 07, 2015, 11:29:09 PM »

Sounds like it would be handy in DSLstats? :D

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ktz392837

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Re: Losing 6db and 20Mb, gaining 6db get 20Mb back?
« Reply #3 on: April 07, 2015, 11:42:37 PM »

Possible, but it could also be the DLM cutting in and out which will knock off some speed if it applies error correction and interleaving.
Its hard to say without inspecting your line stats.

I wouldnt ever let it get down to as low as 1dB even if its hanging in there, because errors will be produced.    3dB is needed to load a single bit into the bins, so dont let it get below that.   Its error count that can cause the DLM to eventually intervene.
From what I understand my interleave is always at 1 on both down and up.  Does interleave let you keep the sync speed at expense of  latency? I have never seen anything apart from 1 which I think is the lowest interleave depth? i would prefer speed over latency but it always seems to be speed drops rather than interleave swirching on.  Guess I will have to hope for g.inp being done on my cab.  My bits per tone is less does that indicate a crosstalk contributor?  Thanks
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WWWombat

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Re: Losing 6db and 20Mb, gaining 6db get 20Mb back?
« Reply #4 on: April 08, 2015, 01:43:28 PM »

If your interleaving depth stays at 1 when your speed drops to 60Mbps, then that indicates DLM is *not* intervening in your line.

Your change in SNRM is therefore more likely to come from an increase in noise - from what you say, it is around 5-6dB of noise.

But we can't say what the noise is; it could be crosstalk from another modem that is being turned on/off. Or from some other source of noise - heating, fluorescent lights, motor, factory, shop, sewage pumps etc. The best way to distinguish would be to figure out the pattern of on/off changes - either manually, or by logging 24x7.

The differences between the bits/tone (or SNR/tone) will likely tell you what tones are being affected by the noise. As Kitz says, 6dB is likely to be 2 bits per tone, on average. Again, the actual pattern of loss over the full spectrum might give you some clues about the type of noise.
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