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Author Topic: Line #4 poorly?  (Read 205 times)

Weaver

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Line #4 poorly?
« on: November 09, 2018, 02:27:18 AM »

Downstream sync in line #4 is down to 1.878 Mbps at 6dB SNRM instead of ~3Mbps downstream at 3dB until the 1 Nov when things started to sporadically go bad. Since the downstream SNRM settings are not equal, this is giving a rather unfair picture and that figure of 1.8Mbps should be  increased by a couple of hundred Mbps, maybe a bit more even. It might be as high as 2.3Mbps at 3dB for comparison purposes. But anyway, I have lost at the very least 700kBps downstream. Upstream is completely fine. AA the ISP is monitoring it, capturing data every hour. No failures reported by line tests but there is a lot of noise coming from somewhere presumably, unless it is a matter of increased attenuation, as I have not looked at all the numbers, and I don’t have a reference data set to compare against, unfortunately.

The AA / Openreach modem status tests report this low downstream speed as an FTB. Does that (hopefully) make it a ‘fault’ by definition ?
« Last Edit: November 09, 2018, 01:58:20 PM by Weaver »
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Ixel

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Re: Line #4 poorly
« Reply #1 on: November 09, 2018, 11:53:30 AM »

FTB - fault threshold breach, can mean that the low sync speed could be considered a fault in itself. However, whether this is actually the case in reality is another question. One can only hope that it is.
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Weaver

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Re: Line #4 poorly?
« Reply #2 on: November 09, 2018, 01:52:28 PM »

I swapped out the modem for another unit. I plugged in a DLink DSL-320B-Z1 in fact, and straight away downstream sync rate is right up to ~2.8 Mbps at 6dB SNRM, so allowing for the fact that this is 6dB SNRM not 3dB like the other modems that is very much full speed.

So either that B10A has gone bad or it is just some weird thing to do with turning everything off and on again ? Suggestions ?

We had some lightning in the distance last month and some days later, on 1 Nov, line #4 or its modem started misbehaving, with reduced downstream sync speeds.

I picked a DLink simply out of convenience, because I have several at hand already set up, and although I have several ZyXEL B10As in my spares cupboard, I am not sure whether or not they have been configured etc yet, and I did not take the time to assess them. That is a job for when I am feeling a bit better.

Later on, I will retest the ZyXEL to see if it has really ‘gone slow’ ie permanently bad.

Do modems ever develop a disease of permanent slowness? Speculating, is it possible that part of the filter or analog front end can get cooked affecting the performance adversely, but the modem still functions, albeit in a substandard fashion? Or is it all or nothing with modems ?
« Last Edit: November 09, 2018, 01:58:33 PM by Weaver »
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Weaver

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Re: Line #4 poorly?
« Reply #3 on: November 09, 2018, 02:28:45 PM »

I found this     https://www.btwholesale.com/content/binaries/broadband_extra/bt_ipstream/handbook/IPstream_Max_handbook_v7.pdf
fairly old doc about DSL Max (20CN). It says somewhere that the FTR used to be 80% of the MSR but set to a particular level according the table of quantised levels in those days.

What is the story for 21CN ADSL and FTR?
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