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

Re: Unusual upstream frequencies
 

how much do you want to bet that there is a 34 and a 64 as well?

Re: Unusual upstream frequencies
 

possibly, but are these likely to be correct, when previously I've only ever seen values ending 00000

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.

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

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

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?

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

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.

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

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.

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.