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-   -   55 DbmV upstream power level (https://www.cableforum.uk/board/showthread.php?t=33644321)

Steve Day 12-01-2009 22:00

55 DbmV upstream power level
 
On wednesday i have a tech coming out to have a look at my connection whose upstream jumped from 50 to 55 last week. currently it is stable but i was just wondering what i can expect the guy to do about it?

I have no splitters just a direct cable from the modem to my incoming cable box, it is the only cable connection i have.

just out of interest

Steve

Stabhappy 12-01-2009 22:04

Re: 55 DbmV upstream power level
 
It could be effecting your service so he will fit a device to lower the power level.

Ignitionnet 12-01-2009 22:54

Re: 55 DbmV upstream power level
 
How's he going to fit something to the modem to lower the upstream transmit power level Stab?

If he can't find anything obvious causing the problem he might have to get a network tech in. With a bit of luck it'll be something simple like a connection not done properly.

moaningmags 12-01-2009 23:28

Re: 55 DbmV upstream power level
 
He may well fit an attenuator between the coax and the modem.

Stabhappy 12-01-2009 23:34

Re: 55 DbmV upstream power level
 
I thought that's what was done when power levels were incorrect? I guess it makes logical sense that it's only possible to boost the signal levels.

moaningmags 12-01-2009 23:40

Re: 55 DbmV upstream power level
 
They can fit attenuators to boost or reduce the power levels.

I stand corrected, attenuators are for downstream power levels and SNR.
The friend who corrected me knows their stuff, so I'll take their word for it.


Another edit after quick tutorial from said friend, the upstream can be adjusted by an attenuator.
This would usually happen at the cab, but if low downstream SNR is causing the upstream power level to increase to be heard by the ubr, fitting an attenuator would fix the SNR issue, lowering the upstream power level.

Stabhappy 12-01-2009 23:51

Re: 55 DbmV upstream power level
 
Mmm. As I thought.

moaningmags 13-01-2009 00:35

Re: 55 DbmV upstream power level
 
Steve

What is your downstream SNR?

Steve Day 13-01-2009 00:45

Re: 55 DbmV upstream power level
 
all other values seem fine.

downstream

SNR 40
power level 7db

the upstream power was until november in the high 40s, then it slid up to 50/51 then after an outage which took down my entire are last week it leapt up to 55 and has stayed there. but at the weekend i had no connection for over 12 hours with "ranging errors" filling my modem logs.

Steve

moaningmags 13-01-2009 00:50

Re: 55 DbmV upstream power level
 
That's a very healthy SNR, so an attenuator won't fix it.
Must be something in the cab causing it, a tech visit is needed, he should check the modem, which one is it?
He should check the cabling, have you made sure the white coaxial cable is screwed in tight and not loose in any way.
If they check out, he should then check the cab at the end of the street.

Steve Day 13-01-2009 03:28

Re: 55 DbmV upstream power level
 
there is a tech coming on wednesday actually.
I created this thread because i knew that here i could get a realistic appraisal of what i should be expecting him to check and what i could check myself.

the modem is 3 year old motorola sb5100 which up to now has been fine but it has afterall been on virtually 24/7 for just over 3 years.

i have reconnected the coax at the modem end and tried it with and without the -6db attenuator that was fitted last year to drop my downstream power level to 8db (i was running at 14db).

Steve

Ignitionnet 13-01-2009 08:59

Re: 55 DbmV upstream power level
 
Quote:

Originally Posted by moaningmags (Post 34714466)
Another edit after quick tutorial from said friend, the upstream can be adjusted by an attenuator.
This would usually happen at the cab, but if low downstream SNR is causing the upstream power level to increase to be heard by the ubr, fitting an attenuator would fix the SNR issue, lowering the upstream power level.

This confuses me a bit how a bad downstream SNR would cause the upstream transmit power level to increase so I'll look into it a bit more and speak to someone who will know, have seen bad downstream SNR and it did not appear to cause modems to increase their transmit power.

Thank you for the information!

caph 13-01-2009 09:06

Re: 55 DbmV upstream power level
 
I've been told by an engineer that my local increase in upstream power is being caused by my "exchange" being upgraded to 50Mb.

Ignitionnet 13-01-2009 19:16

Re: 55 DbmV upstream power level
 
Quote:

Originally Posted by moaningmags (Post 34714466)
Another edit after quick tutorial from said friend, the upstream can be adjusted by an attenuator.
This would usually happen at the cab, but if low downstream SNR is causing the upstream power level to increase to be heard by the ubr, fitting an attenuator would fix the SNR issue, lowering the upstream power level.

I had another thought about this.

If bad downstream SNR were causing issues with upstream it would be because the modem were not seeing the periodic station maintenance responses from the uBR / CMTS, so it would increase transmit power thinking it was not being heard. When it did actually get a response from the CMTS it would be along the lines of 'Oi stop shouting, drop your transmit power down xdBmV' so I can't really see how it would reduce Tx power long term.

What it might resolve is large numbers of power adjustments due to the modem not seeing the range response from the CMTS and hence incrementing transmit power by the DOCSIS standard amount, however if the downstream path is so munted that the modem is missing large amounts of range responses and periodic station maintenances from the CMTS the upstream power is a total non-issue.

A connection that would suffer issues like this would be very, very broken indeed and upstream Tx power would be the least of worries on a connection like this. It would likely be too busy losing QAM sync on the downstream to be bothered what the upstream is doing.

---------- Post added at 18:16 ---------- Previous post was at 18:14 ----------

Quote:

Originally Posted by caph (Post 34714579)
I've been told by an engineer that my local increase in upstream power is being caused by my "exchange" being upgraded to 50Mb.

That sounds like BS to me. Doesn't make any sense at all that your upstream power would need to rise to accomodate 50Mbit and the DOCSIS 3 overlay.

caph 13-01-2009 20:29

Re: 55 DbmV upstream power level
 
Quote:

Originally Posted by Broadbandings (Post 34714971)
That sounds like BS to me. Doesn't make any sense at all that your upstream power would need to rise to accomodate 50Mbit and the DOCSIS 3 overlay.

Sounds like it could be BS to me too but the only logical conclusion to that is that service engineers deliberately lie to customers to fob them off. It's possible but it leaves a bad taste in my mouth. His words were more along the lines of - they're up to their neck in it and the power levels are all over the place and will be until they're finished.

---------- Post added at 19:29 ---------- Previous post was at 18:50 ----------

Quote:

Originally Posted by Broadbandings (Post 34714971)
If bad downstream SNR were causing issues with upstream it would be because the modem were not seeing the periodic station maintenance responses from the uBR / CMTS, so it would increase transmit power thinking it was not being heard. When it did actually get a response from the CMTS it would be along the lines of 'Oi stop shouting, drop your transmit power down xdBmV' so I can't really see how it would reduce Tx power long term.

What it might resolve is large numbers of power adjustments due to the modem not seeing the range response from the CMTS and hence incrementing transmit power by the DOCSIS standard amount, however if the downstream path is so munted that the modem is missing large amounts of range responses and periodic station maintenances from the CMTS the upstream power is a total non-issue.

A connection that would suffer issues like this would be very, very broken indeed and upstream Tx power would be the least of worries on a connection like this. It would likely be too busy losing QAM sync on the downstream to be bothered what the upstream is doing.

Sorry to jump thread but you are almost exactly describing my current UCD problem apart from the downstream problem.

My event log is showing continual critical errors of "Started Unicast Maintenance Ranging - No Response received" followed by the UDC message. And my upstream power levels keeps getting higher and higher (hit 60db tonight). The only thing is my downstream power is 0.6 and my downstream SNR is a healthy 36.3. Can you think of any reason why my modem keeps shouting but not getting a reply?


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