55 DbmV upstream power level [Archive]

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Steve Day

12-01-2009, 21:00

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, 21:04

It could be effecting your service so he will fit a device to lower the power level.

Ignitionnet

12-01-2009, 21:54

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, 22:28

He may well fit an attenuator between the coax and the modem.

Stabhappy

12-01-2009, 22:34

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, 22:40

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, 22:51

Mmm. As I thought.

moaningmags

12-01-2009, 23:35

Steve

What is your downstream SNR?

Steve Day

12-01-2009, 23:45

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

12-01-2009, 23:50

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, 02:28

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, 07:59

caph

13-01-2009, 08:06

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, 18:16

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 ----------

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, 19:29

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 ----------

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?

Steve Day

13-01-2009, 22:44

ok this is tonights installment...

when the cable installer did his job 3+ years ago he ran at my request a fairly long black cable from the box outside my house, thru the garage and up the back wall to the room i wanted the internal cable point in.

tonight...
i pulled on the black cable which was turned hard thru 90 degees to exit thru a doorframe, giving it some slack and presto.. my upstream suddenly became 45-47.

i will of course have to discuss this with the engineer tomorrow as to whether the cable is busted inside the sheathing.

whats inside the black cables that go from the street to your house? is it fibre optic? and can they indeed fracture or become a source of interference if bent hard enuf?

Steve

moaningmags

13-01-2009, 22:56

It's coaxial cable from the street to the house.
If it's damaged, they may need to book a repull, re-laying the cable to your house.

Steve Day

13-01-2009, 23:17

ok i am ammending the description in my last post. the cable from the street ends in a small box on my house front wall. from this small box exits the potentially faulty black cable which goes across my front wall, thru the garage and up the back wall to the internal cable modem socket/white box.

i have just been outside tracing all this stuff like i should have earlier :)

i hope this makes more sense now :)

is this black cable still coax? only it seems very tough and "plastic" to be coax, i doesnt seem to want to bend easily.

Steve

Stabhappy

13-01-2009, 23:37

It doesn't bend easy because it's full of soft metal, as aposed to plastic and glassy materials like that in fibre.

LaineY

14-01-2009, 01:44

Yeah.. its the Coax Cable..

I have a similar set up to you...

It comes from the Main Headend to the Regional Headend for your area.. then normally from there to the box in your street (Normally Green).. Converts from Optical/Fibre (Light) to Coax (RF) where it runs along the ground through trunking to the Sub Box (Depends, Closer to the property) then to the Omni box (Box with a cover over it) which is normally outside your wall...then.. there will be the same cable (Black Coax) which is running along up through your garage and to upstairs.

If this is in anyway Damaged a repull will be required to get that Coax replaced..

Any Upstream/Downstream signal issues i have had .. have normally been resolved @ the box in the street or the Sub Box (Manhole) in the ground out front..

In 14 years i have only had to have the power levels repaired twice..
Everytime my problem was resolved....

Hope this helps...

Ignitionnet

14-01-2009, 13:01

Quick FYI from the newsgroups:

Hi Broadbandings,

I must apologise, I have been misinformed regarding the use of attenuators.
As you suspected you cannot add an attenuator to lower the upstream power
level. Sorry for the mix-up.

-- Kind Regards Lee Grant Virgin Media Technical Support

---------- Post added at 12:58 ---------- Previous post was at 12:54 ----------

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.

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?

Hrm they might be doing work cleaning up the network in preparation for the 50Mbit but it shouldn't be breaking things and extra extra combining should be done at the hubsite's RPM and not affecting current services as the combining will be to the new equipment not the current stuff.

With my tech hat on and being sober for a change, you are losing your upstream channel - there's too much attenuation on your upstream path and the CMTS / uBR isn't able to hear you properly and is requesting transmit power increase, or doesn't hear you at all - which is why you aren't getting a ranging response - the CMTS can't respond when it didn't hear anything.

The UCD message likely indicates you have changed upstream, you lose your lock on the upstream you were on and move to a new one, the new one has a different UCD hence the message.

You really do need a tech to sort your return / upstream path.

---------- Post added at 13:01 ---------- Previous post was at 12:58 ----------

is this black cable still coax? only it seems very tough and "plastic" to be coax, i doesnt seem to want to bend easily.

Steve

Decent coax not the 99p for a kilometre stuff is quite tough and 'plastic' - it's supposed to have multiple levels of shielding for the inner core of the cable ;)

Joxer

14-01-2009, 13:12

The common kind of coaxial cable used for TV aeriels etc has a copper core, the kind used for cable TV/Broadband has a stainless steel core with a copper coating, as you probably are aware stainless steel is a lot harder to bend than copper, though it is more brittle so a 90 degree bend could have caused a fracture which while not a complete break could degrade performance and could also be frequency specific.

Ignitionnet

14-01-2009, 13:17

That it is much cheaper than a pure copper core is merely a bonus ;)

General Maximus

14-01-2009, 13:23

I agree, the tensile strenght of steel is conisderably greater than that of copper. http://en.wikipedia.org/wiki/Tensile_strength

Feenix

14-01-2009, 13:24

and to reduce costs, and the fact that the copper is only required on the outside of the core due to skin effects. 90 degree bends are know to have serious attenuation issues on coax, hence the minimum bend radius specifications.

Joxer

14-01-2009, 13:31

Maybe I am wrong about the stainless bit, but I would have thought it would be to add tensile strength rather than flexibility.

---------- Post added at 13:31 ---------- Previous post was at 13:29 ----------

Actually, thinking about it, the crushing of the dielectric will cause issues as well.

Ignitionnet

14-01-2009, 13:34