dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
1695
share rss forum feed

itwong

join:2012-02-18
Sacramento, CA

[Speed] New Blast Plus install, how's my stats?

 
Click for full size
got mine installed today and it turns out the drop is already run to the side of my house. very nice. All the tech has to do is to hook up and change a few setting to the tap. In my neighborhood, all utilities are run underground and the tap i am connected to is across the street. Had a Arris CM820A DOCSIS 3.0 modem and got 8 channels bonding downstream and 3 channels bonding upstream. Here's a little screenshot of my stats.

The tech told me all of california should get speed upgrade starting on 03/19 which is tomorrow. Blast will be upgraded to 50/10 I believe.

travelguy

join:1999-09-03
Santa Fe, NM
Your speeds are right on for a pre-increase area. Your power levels look good - excellent on the upstream side. Good tech and good plant. Your ping is a little high - I see between 5-9, but there's nothing you can do about it unless you have a router that's messing things up. It won't cause any problems and you won't see any impact. You might try rerunning the test plugged right into the modem.

itwong

join:2012-02-18
Sacramento, CA
The tech put in a ticket for crews to come out and reinstall the drop to my house. He noticed something when he checked the tap across the street. Although my line is fine now, it might have a problem in the future. That's why he put in a request for re-running the drop to my house.


Johkal
Cool Cat
Premium,MVM
join:2002-11-13
Happy Valley
kudos:10
reply to travelguy
The Upstream is on the extreme low end. Not preferable or recommended. 40+ dBmV to 49 dBmV is recommended.

travelguy

join:1999-09-03
Santa Fe, NM
You don't understand what the upstream number means. Unlike the downstream number, which is the level your modem is receiving, the upstream number is what your modem is transmitting. The level is totally controlled by the CMTS and is set based on what levels the CMTS is seeing. A low upstream number means that there is very little noise or signal loss from the modem to the CMTS, therefore lower is better. 49 dBmV is getting close to the max your modem will push which is not a good thing.


gHiDoRa

join:2002-08-05
Memphis, TN
reply to itwong


Johkal
Cool Cat
Premium,MVM
join:2002-11-13
Happy Valley
kudos:10

1 edit

1 recommendation

reply to travelguy
55 dBmV is the observed max where a modem may see disconnects.
As for understanding signal levels; LOL! That's funny!

»Comcast High Speed Internet FAQ »What should my Signal Levels be?

"*Recommended upstream signal levels are +35 dBmV to +49 dBmV."

travelguy

join:1999-09-03
Santa Fe, NM
said by Johkal:

"*Recommended upstream signal levels are +35 dBmV to +49 dBmV."

Unfortunately, there is no support for this statement. OTOH, if you look in the DOCSIS 3.0 spec, you will find the following:

5.3 Transmission Levels
The nominal power level of the upstream CM signal(s) will be as low as possible to achieve the required margin above noise and interference. Uniform power loading per unit bandwidth is commonly followed in setting upstream signal levels, with specific levels established by the cable network operator to achieve the required carrier-to-noise and carrier-to-interference ratios.
Which basically means that as long as the SNR number at the CMTS is good, the power level can be as low as possible. Making a blanket statement that the power level is too low without knowing the SNR is uninformed.


AnonMan

@comcast.net
reply to Johkal
You can have low US power level and still be high noise.

My US is 38 and often times my US SNR goes into the 20's and knocks everyone out. (The entire node dips due to someone who keeps hooking crap up they shouldn't. It gets investigated, they get cut/fixed and all good again till next person does).

That said, US power level, anything over 33 is considered fine.
That whole needs to be above 40 is crap. If the signal is getting to the CMTS it doesn't need to be higher. This signal also does not increase as noise does as people keep saying, it increases if no return signal is detected at all. Noisy or not either no signal gets to the end or signal does. The noise just impacts it being able to hold data. The only exception to this too low myth is if an AMP is cranked too high which also increases noise but causes modem level to transmit lower as amp boosts it and the AMP needs to be turned down which in turn will increase US power level of the modem, beyond that no true "too low" really exists. This is something that is just told and taught to people and often times they are told various misinformed things that "sound" like the reason but are totally wrong.

Think of it this way, take 4 people with 2-way radios, same distance apart. Two people are on clean channels and can talk and hear each other fine. The other 2 are on noisy channels that have a lot of interference. When they hit the button the signal will still get to the other radio but it will be noisy, unclear or just simply statistic due to the noise. Remember, CMTS work based on radio frequencies, just on the wire vs. wireless. While generally more power can help something noisy be heard more clear for cable systems that isn't what the US does. It increases only when no signal is detected or attenuation is increased.


Johkal
Cool Cat
Premium,MVM
join:2002-11-13
Happy Valley
kudos:10
said by AnonMan :

That said, US power level, anything over 33 is considered fine.
That whole needs to be above 40 is crap.

You have to know the difference between "Needs" & "Recommended".


AnonMan

@comcast.net
Even the recommended part is not true.

That is said because the general thought is if it's too low that means an amp must be cranked too high thus dirty signal amplified also but more often vs. not this is not the case.

You can have US power in the 20's and be perfectly fine, esp. if you are very close to the CMTS. At the end of the day US power should only be stated as "shouldn't go over 50's" and SNR shouldn't go below 30's for best results. All of the rest is irrelevant on it. Just like SNR shouldn't have any upper limit because higher is cleaner, US power level has no lower limit so long as SNR is within spec as lower is better so long as it's clean...

Anyone with low US Power just need to find out SNR and if it's good not worry about it and def don't go putting attenuators or splitters to try to raise US power as that is artificial and only changes from modem to the splitter/attenuator anyway. If SNR is bad the techs will need to make adjustments or clean noise. This only applies to US, DS is another story.


nerdburg
Premium
join:2009-08-20
Schuylkill Haven, PA
kudos:1

1 recommendation

said by AnonMan :

You can have US power in the 20's and be perfectly fine, esp. if you are very close to the CMTS. At the end of the day US power should only be stated as "shouldn't go over 50's" and SNR shouldn't go below 30's for best results.

This is basically true, but here is always going to be variation depending on physical location, the design of the system, transmission schemes and noise levels. The recommendations are based on Comcast's own technical specifications -- Comcast tech's are generally required to have an upstream of 35-50dBmV at the time of install. The operational range of modems is much greater than the Comcast specifications, so in most cases the modems will tolerate signals significantly out of spec.

andyross
Premium,MVM
join:2003-05-04
Schaumburg, IL
reply to Johkal
said by Johkal:

55 dBmV is the observed max where a modem may see disconnects.
As for understanding signal levels; LOL! That's funny!

»Comcast High Speed Internet FAQ »What should my Signal Levels be?

"*Recommended upstream signal levels are +35 dBmV to +49 dBmV."

But, with upstream bonding, you'd want to keep it in the low-mid 40's at best, to leave some overhead. The max transmit is 51-52dB with 3-channel bonding.

travelguy

join:1999-09-03
Santa Fe, NM
reply to nerdburg
said by nerdburg:

The recommendations are based on Comcast's own technical specifications -- Comcast tech's are generally required to have an upstream of 35-50dBmV at the time of install. The operational range of modems is much greater than the Comcast specifications, so in most cases the modems will tolerate signals significantly out of spec.

The problem is that low side number. If as is the case with the OP, the US power level is less than 35, what are you going to do? Stock response is place a low frequency attenuator on the drop. Well, that would cause the modem to up its power output to compensate, but what does that do besides lower the headroom of the modem? It doesn't change anything (level or noise) between the filter and the CMTS and the CMTS sees the same signal level.


nerdburg
Premium
join:2009-08-20
Schuylkill Haven, PA
kudos:1


The problem is that low side number. If as is the case with the OP, the US power level is less than 35, what are you going to do? Stock response is place a low frequency attenuator on the drop.

OP's level may be fine in his system. If it's working, I wouldn't do anything. If OP has issues, then Maintenance needs to make adjustments to the cable plant. It's pretty common knowledge amongst cable nerds that you can't attenuate upstream signal, but a lot newer techs don't understand that. Heck, I didn't understand it either for a long time.

travelguy

join:1999-09-03
Santa Fe, NM
said by nerdburg:

If it's working, I wouldn't do anything.

I agree!

said by nerdburg:

If OP has issues, then Maintenance needs to make adjustments to the cable plant. It's pretty common knowledge amongst cable nerds that you can't attenuate upstream signal, but a lot newer techs don't understand that. Heck, I didn't understand it either for a long time.

That's my point. I wasn't proposing an attenuator, Just pointing out that it wouldn't buy anything. My real question is what adjustments to the cable plant? You have a link between the CMTS and the CM. The CMTS measures the signal and noise and commands the CM to output at a certain level. What would you do that would cause the CMTS to increase that CM US command?


THZNDUP
Deorum Offensa Diis Curae
Premium
join:2003-09-18
Lard
kudos:2
said by travelguy:

... My real question is what adjustments to the cable plant? You have a link between the CMTS and the CM. The CMTS measures the signal and noise and commands the CM to output at a certain level. What would you do that would cause the CMTS to increase that CM US command?

Short answer-balance that link between the CMTS and CM(s) by adjusting/correcting the slope and gain in the reverse amplifiers. Additional work would be to correct any cable/connector/passive problems in between.
--
one should not increase, beyond what is necessary, the number of entities required to explain anything

travelguy

join:1999-09-03
Santa Fe, NM
said by THZNDUP:

Short answer-balance that link between the CMTS and CM(s) by adjusting/correcting the slope and gain in the reverse amplifiers. Additional work would be to correct any cable/connector/passive problems in between.

Thank you - that makes sense. What I think you are saying is that low output from a CM could be a symptom of one or more reverse amps turned up high to compensate for signal loss. Fix the signal loss, you can reduce the gain of the reverse amp. Reduce the gain of the reverse amp and the CM output can be increased.


THZNDUP
Deorum Offensa Diis Curae
Premium
join:2003-09-18
Lard
kudos:2
As well as minimize the contributory effects of running the reverse amps out of their system design specs or an out of spec amp or return path ingress or a flaw in the system design or.......

The most recent adjustments(?) here have resulted in me losing about 5db both up and down. Was +5dn/+40up now 0db down and +35db up. Did get about a 3db increase in downstream SNR though.

A db here, a db there and pretty soon you're talking some real signal.


--
one should not increase, beyond what is necessary, the number of entities required to explain anything


Johkal
Cool Cat
Premium,MVM
join:2002-11-13
Happy Valley
kudos:10
reply to andyross
said by andyross:

said by Johkal:

55 dBmV is the observed max where a modem may see disconnects.
As for understanding signal levels; LOL! That's funny!

»Comcast High Speed Internet FAQ »What should my Signal Levels be?

"*Recommended upstream signal levels are +35 dBmV to +49 dBmV."

But, with upstream bonding, you'd want to keep it in the low-mid 40's at best, to leave some overhead. The max transmit is 51-52dB with 3-channel bonding.

Looks like you didn't read any posts before that one. Read my 1st post.
--
In God we trust; all others bring data!