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Parad0xxr
@comcast.net

Parad0xxr

Anon

[Connectivity] 64QAM?

Not sure how long this has been this way, but I noticed all 3 of my upstreams are 64QAM now. I know somewhat recently the 1st was always 16QAM. Northeast Philly here...

Will this make any difference for my connection? speed/stability? Or no...

DarkLogix
Texan and Proud
Premium Member
join:2008-10-23
Baytown, TX

DarkLogix

Premium Member

[Connectivity] Re: 64QAM?

I think 64QAM is supposed to have more bandwidth per channel.

telcodad
MVM
join:2011-09-16
Lincroft, NJ

1 recommendation

telcodad to Parad0xxr

MVM

to Parad0xxr
Those 16QAM "TDMA" upstream channels were used by DOCSIS 1.X devices that are now no longer being supported. Consequently, these lower-speed, legacy channels are being removed in many markets now, and replaced with higher-speed, 64QAM "ATDMA" ones used by newer D2 and D3 devices.

From the FAQ page »Comcast High Speed Internet FAQ »What is QAM? , you can see that a 5.12 MSymb/sec 64QAM channel provides 3X the data rate capacity than a 2.56 MSymb/sec 16QAM one (27 Mbps vs 9 Mbps).
HerronScott
join:2004-12-23
Staunton, VA

HerronScott to Parad0xxr

Member

to Parad0xxr
We only have 2 upstream channels and they finally switched both to 64QAM not too long ago.

Scott

telcodad
MVM
join:2011-09-16
Lincroft, NJ

telcodad

MVM

BTW - If other upstream (or downstream) carrier(s) are ever added to the system, I believe your modem will then need to be rebooted in order for it to detect/use it/them.
telcodad

telcodad to Parad0xxr

MVM

to Parad0xxr

Re: [Connectivity] 64QAM?

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said by Parad0xxr :

Not sure how long this has been this way, but I noticed all 3 of my upstreams are 64QAM now. I know somewhat recently the 1st was always 16QAM. Northeast Philly here...

BTW - My system changed like that about 3 months ago, when I found that my ARRIS TM822G eMTA had rebooted by itself overnight. Above is the upstream carrier arrangement before and after.
Brocktoon
join:2009-08-11
Fairless Hills, PA

Brocktoon

Member

said by telcodad:

BTW - My system changed like that about 3 months ago, when I found that my ARRIS TM822G eMTA had rebooted by itself overnight. Above is the upstream carrier arrangement before and after.

Just north of Philly in lower Bucks County ... we also switched over to all 64 QAM about 3 months ago. I think 64 QAM requires a 'cleaner' upstream than 16 QAM, but I've noticed a lot less T3 errors since the switchover.

camper
just visiting this planet
Premium Member
join:2010-03-21
Bethel, CT

camper

Premium Member

said by Brocktoon:

I think 64 QAM requires a 'cleaner' upstream than 16 QAM

 
Yup. TNSTAAFL.

The higher data rate of 64-QAM is more sensitive to line noise.
boontonflyer
join:2004-07-05
Somerset, NJ

boontonflyer

Member

Your reference to "TNSTAAFL" caused me to look it up. I thought it was "TANSTAFFL" BUT you were right. I now know the (apparently correct) derivation. I always thought this was a reference to the 1920's lunch in a bar that was "free" but you really paid for it in the price of the drinks.

Paul
Brocktoon
join:2009-08-11
Fairless Hills, PA

Brocktoon

Member

said by boontonflyer:

Your reference to "TNSTAAFL" caused me to look it up. I thought it was "TANSTAFFL" BUT you were right. I now know the (apparently correct) derivation. I always thought this was a reference to the 1920's lunch in a bar that was "free" but you really paid for it in the price of the drinks.

Paul

For me, I consider it the 4TH LAW OF THERMODYNAMICS ... and I hold a degree in Chemical Engineering
boontonflyer
join:2004-07-05
Somerset, NJ

boontonflyer

Member

I did some more "googling". Apparently there are several derivations (ie a 1961 book, the "free lunch " at saloons in the 1890-1920's etc., and a few more). So much for trivia.

Paul

camper
just visiting this planet
Premium Member
join:2010-03-21
Bethel, CT

2 edits

camper to boontonflyer

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said by boontonflyer:

you were right

 
Sometimes I get lucky.

But, truth be told, I was really thinking of the acronym you cite, "TANSTAFL", but I couldn't remember the exact words.

So I guessed the phrase and posted the acronym of the phrased I surmised.

Thanks for the correction.

In any case, and trying to pull this thread back to the topic.... in general the more data you try to pump through a carrier, the more sensitive to external aberrations the data rate will be.

There is only so much bandwidth available in any carrier, and that bandwidth is shared between the actual data and the noise. The "cleaner" you keep the carrier, the less bandwidth the noise will occupy and the more bandwidth your data can claim as its own.

btw, here's a cool animated GIF showing how 16-QAM works.
»en.wikipedia.org/wiki/Qu ··· tion.gif
boontonflyer
join:2004-07-05
Somerset, NJ

boontonflyer

Member

This discussion brings back memories. In the 1970's I was working for a "supervisory control/telemetering" company. Our initial products were limited to the "Nyquist" theory (one bit/cycle of bandwidth[FSK]). Later products started to use QPSK (Quadrature Phase Shift Keying). It allowed us to get higher bit rates in the systems over dedicated telephone lines .

Paul

camper
just visiting this planet
Premium Member
join:2010-03-21
Bethel, CT

camper

Premium Member

 
Ah yes, the Nyquist Theory.... know it well.