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 QumahlinNever Enough TimePremium,MVM
join:2001-10-05
united state | reply to visiontruth
Re: QAM and Modem said by visiontruth:
Please read »[Connectivity] Slow Download Speeds after 256 QAM Upgrade I made a long post at the bottom from a forum at comcasts Help forum.
You guys this is QAM256 upgrade breaking many not so good wired areas. They want more bandwidth more customers more money. COMPLAIN read this post. I will be putting up a petition website full of information soon. Comcast cant just let people suffer, btw even if you upgrade your modem to Motorola or others, go play a game or any other streaming connection, you will still see the packet loss it's still there. This QAM 256 upgrade is breaking not all but many areas, you see QAM256 sticks the packets closer together and is more prone to problems and spikes. You are seeing the result of a implementation of a technology that the hardware in your area is just simply not ready for. Its not your modems just happens that some modems deal with it better than others, none the less the best modem will still stutter, spike, and timeout on a constant rotating basis for the last 2 months since these upgrades started.
I admit the QAM "upgrade" in some areas is causing issues for areas that already had slight signal problems which then impacted them further once 256 is implemented due to a cleaner signal being needed.
Saying QAM256 works by "sticking packets closer together" isn't exactly correct and doesn't begin to address how QAM modulation works and the differences between 64 decision points and 256 decision points.
QAM256 is being rolled out slowly exactly for reasons like this, because the only true way to fix the issues is for us to set the CMTS to use QAM256 modulation and then fix the areas that experience problems due to signal and other issues.
It doesn't have anything to do with the hardware "not being ready for it" but rather the fact that no plant is perfect and their will always be problem areas.
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 NerdtalkerWorking Hard, Or Hardly Working?Premium,MVM
join:2003-02-18
Tucson, AZ | 
Bit Error Rate |
said by Qumahlin:
I admit the QAM "upgrade" in some areas is causing issues for areas that already had slight signal problems which then impacted them further once 256 is implemented due to a cleaner signal being needed.
Saying QAM256 works by "sticking packets closer together" isn't exactly correct and doesn't begin to address how QAM modulation works and the differences between 64 decision points and 256 decision points.
It doesn't have anything to do with the hardware "not being ready for it" but rather the fact that no plant is perfect and their will always be problem areas.
I'd have to agree 100% Qumahlin, I've read the post in question (the one you're replying to) almost 3 times in the forum, and, for the most part, it is either vague or inaccurate.
No offense to the poster, but whoever wrote the post in question obviously never passed High School English with all those run-ons...
But I'm getting besides myself. There seems to be almost a sudden pre-occupation with QAM lately in here after we saw one topic (»[Connectivity] Slow Download Speeds after 256 QAM Upgrade) where a speed decrease accompanied a switch to 256QAM modulation. Whether these two events are simply coincidence, or are directly related, is the purpose of the thread, and is as of yet undecided. Personally, I doubt that the switchover would have that drastic of an effect.
Now, I'd like to address "the" post (a copy of some thread somewhere).
Its amazing that "Anon854503" is going to start a petition against the modulation switchover. Obviously, he knows nothing other than that "magically" his service isn't working, and, so as all good people must do, he wants to start banging his drums. While I'm not going to even venture to spend my time/effort fixing his particular problem, I think I can counter the "OH NOS!1! MY AREA HAS 256QAM!!1" misinformation going around.
As Qumahlin has already stated, Anon854503 says something totally wrong: said by Anon854503:
QAM256 basically fits all the packets closer together so it is much more prone to spikes and other problems, I have heard some reports about RCA modems dealing with the problem better, I would like to know if anyone can deal with this.
Okay, First off the bat, 256QAM DOES NOT stick packets closer together, it does nothing of the sort. Instead of spending 10 minutes of my time trying to put it right, I'll quote somebody: said by »en.wikipedia.org/wiki/Quadrature···ulation:
In digital applications, the modulating signal is generally quantised in both its in-phase and 90° components. The set of possible combinations of amplitudes, as shown on an x-y plot, is a pattern of dots known as a QAM constellation.
The pattern of dots mentioned in my quoted research article are also called decision points, meaning, the cable modem has to decide (after these points are plotted) where in the QAM table the point lies.
This is difficult from an engineering point of view, because some points are on the line, close to being on one side, or may not fit the logical pattern of what comes next. Add noise to the mess, and it becomes harder for the modem to decide correctly. This is commonly reflected in the SNR.
The number before QAM (for example 16QAM) refers directly to the number of decision points in the constellation. Meaning, 256QAM has 192 more decision points than 64QAM. The attached picture shows how much of a difference that makes in the BER (Bit Error Rate), or, as Anon854503 put it (intentionally or not) the packet loss. As you can see, it really isn't that dramatic. Sure, it might make or break somebody's sync if they've got terribly crappy cabling, but otherwise people shouldn't notice the difference. I sure as heck didn't.
There's nothing (in regards to actual documents) where its been decided or even proven that any current modem handles noise better than another one. Anyways, most modems use one of a few Broadcom or TI chipsets available, so they're all about the same when it comes to signal processing.
As to Anon854503's COMPLAIN and PETITION rantings, I'd like to pose a question, what if they switched to 256QAM to give you faster downloads, instead of squeeze more people onto a downstream channel as you speculate. Would you petition then?
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Touch a thistle timidly, and it pricks you; grasp it boldly, and its spines crumble. -William S. Halsey | |
thumbs down from:
Nerdtalker 
| As to Anon854503's COMPLAIN and PETITION rantings, I'd like to pose a question, what if they switched to 256QAM to give you faster downloads, instead of squeeze more people onto a downstream channel as you speculate. Would you petition then?
lmao what kind of question is that , it obvious the guy is pulling his hair out over the problem and just wants the **** fixed | |
thumbs down from:
Nerdtalker
| i live in the independence area as well have the node in my back yard for the area had 2 techs out and basicly they said there not gonna do nothing to fix the problem with online gaming and the qam256 problem were having | |
QumahlinNever Enough TimePremium,MVM
join:2001-10-05
united state | said by annonn:
i live in the independence area as well have the node in my back yard for the area had 2 techs out and basicly they said there not gonna do nothing to fix the problem with online gaming and the qam256 problem were having
ok just some FYI's...i've seen multiple posts both here and the comcast.net forums about people saying they saw techs out at the node and it was them upgrading to QAM256.....This is incorrect the modulation is set at the headend via the CMTS console. The node does not have to have anyone go out to it, or have anything changed on it.
Next, I don't know what techs you talked to, but i'm willing to bet that they know nothing about the situation, nor do they work in engineering so them saying "nothing will be done to fix it" was nothing more then a quick way for them to say what they REALLY meant which is "we can't do anything to fix it because we are field techs and it's not simple signal issue"
In general field techs are not well trained on the data side of the network. Alot of them don't know much or only know the basics about DOCSIS, CMTS's, QAM/QPSK in relation to the node/modem, etc, etc.
Then on the other hand I know field techs who probably know more then some of the lower system engineers and could probably replace them but aren't hired due to lack of proper credentials to certify their knowledge.
So for a field tech to tell you they aren't doing anything to fix a problem he most likely doesn't understand is just wrong.
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Forum Posts:5307 | |
NerdtalkerWorking Hard, Or Hardly Working?Premium,MVM
join:2003-02-18
Tucson, AZ | said by Qumahlin:
Then on the other hand I know field techs who probably know more then some of the lower system engineers and could probably replace them but aren't hired due to lack of proper credentials to certify their knowledge.
Not to hijack, but out of curiosity, what sort of credentials/certifications can you get regarding DOCSIS, and Cable in general?
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Touch a thistle timidly, and it pricks you; grasp it boldly, and its spines crumble. -William S. Halsey | |
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