Unusual upstream frequencies
22-04-2017, 16:37
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#1
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cf.geek
Join Date: Jun 2008
Posts: 804
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Unusual upstream frequencies
I've mentioned this in passing in a different thread.
This week the New Malden CMTS upgrades started to happen - I was moved to a new CMTS as part of this work and went from 12 to 16 down stream channels.
Upstream stayed the same, but not sure if modulation changed to 64 QAM as the Hitron business hub doesn't display that.
What I do find is the frequencies of the upstreams are varying a bit - this didn't happen before. Previously all frequencies ended in 00000 but now I get varying ones show below. Is this normal?
Performance upstream is slightly worse since the changes.
Upstream Overview
Port Frequency (Hz) BandWidth Modulation Power (dBmV) Channel
1 30999944 6400000 ATDMA 39.750 2
2 37599954 6400000 ATDMA 43.250 1
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22-04-2017, 17:21
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#2
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Ran Away
Join Date: Nov 2008
Location: Lincoln
Services: phone + 1gbit BB + SkyQ
Posts: 11,021
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Re: Unusual upstream frequencies
how much do you want to bet that there is a 34 and a 64 as well?
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22-04-2017, 17:53
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#3
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cf.geek
Join Date: Jun 2008
Posts: 804
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Re: Unusual upstream frequencies
possibly, but are these likely to be correct, when previously I've only ever seen values ending 00000
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22-04-2017, 18:32
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#4
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Ran Away
Join Date: Nov 2008
Location: Lincoln
Services: phone + 1gbit BB + SkyQ
Posts: 11,021
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Re: Unusual upstream frequencies
me too, I checked mine and they are still ending in zeroes. You wonder if it is a coincidence or a new logical numbering system for the frequencies.
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22-04-2017, 18:44
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#5
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cf.geek
Join Date: Jun 2008
Posts: 804
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Re: Unusual upstream frequencies
possibly - though they seem to vary if I restart the Hitron - though the first three digits stay the same. I wondered if they is some drift or a local amplifier is distorting things a bit
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22-04-2017, 21:00
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#6
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cf.addict
Join Date: May 2010
Posts: 336
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Re: Unusual upstream frequencies
I'm a business engineer, noticed this on a Hitron a while back. Nothing to worry about. It's just the way the hitron is reporting it. The frequencies are 31mhz and 37.8mhz. That is the centre point of the 6.4mhz wide carrier, so the carriers go 3.2mhz either side of that figure. The hitron just isn't using the centre point as a label
---------- Post added at 21:00 ---------- Previous post was at 20:59 ----------
Or may be 37.6 I can remember, it was a while during my network engineer days I last looked in any detail at spectrum
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22-04-2017, 21:03
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#7
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cf.geek
Join Date: Jun 2008
Posts: 804
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Re: Unusual upstream frequencies
Ah ok thanks for that vm_tech DO you know of any way to get the Hitron to reveal whether the upstreams are 16QAM or 64QAM?
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22-04-2017, 21:07
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#8
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cf.addict
Join Date: May 2010
Posts: 336
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Re: Unusual upstream frequencies
I'm not too sure if I'm honest I don't do much on the hfc side of things these days. Next time I work on one I'll have a look
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22-04-2017, 21:11
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#9
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cf.geek
Join Date: Jun 2008
Posts: 804
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Re: Unusual upstream frequencies
ok great thanks. I haven't found a way. The old SH1 with business firmware did report that as it did the operational config from the config file. Can't see either on the Hitron.
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23-04-2017, 21:13
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#10
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cf.geek
Join Date: Jun 2008
Posts: 804
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Re: Unusual upstream frequencies
What I also notice is that at times I will lock onto
30999944 37599954 As a pair of downstreams and at other times 30999979 & 24399991
The common one is always 309xxxxx but the one it pairs with varies. Does this imply there is actually a group of 3 downstreams but not configured correctly and the modem is lockign onto only two of them?
Upstream performance has been worse since this work was carried out, hence checking this part more.
The CMTS is now nmal25-2-0
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24-04-2017, 08:54
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#11
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FORMER Virgin Media Staff
Join Date: Dec 2010
Location: Warrington
Posts: 4,737
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Re: Unusual upstream frequencies
It's nothing to worry about. Or rather, it's Virgin's issue to worry about and believe me, all those metrics are constantly fed back to them.
If you have a problem, call them up instead of trying to diagnose it yourself (though it's always useful to know what to look for).
If you don't have a problem, don't worry about it.
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24-04-2017, 21:18
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#12
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cf.geek
Join Date: Jun 2008
Posts: 804
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Re: Unusual upstream frequencies
Well the problem is that when I have channels at 30900000 and 24300000 upstream performance is good, but when I get 30900000 and 37500000 upstream performance drops by about 50% so yes there is an issue.
I agree it's VMB to diagnose, but was keen to understand what people that know a lot more about how this works than I do think about it, ie is this is really a three channel group that isn't working as a 3 channel group correctly?
It wouldn't be the first time we have seen details of a new CMTS go live with a config error that was discussed here.
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