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tshirt
Premium,MVM
join:2004-07-11
Snohomish, WA
kudos:4
reply to bernardc

Re: [Speed] Download/upload ratio: Is it physics?

DOCSIS is asymmetrical by design, which wikipedia can easily explain
»en.wikipedia.org/wiki/DOCSIS


bernardc

join:2009-12-13
Berkeley, CA

Thank you, tshirt. But I've been to that page before posting the question, and the word "asymm*" does not appear. And according to the standard, the maximum bandwidth for upstream and downstream are only different by a factor of 1.4, a far cry from the 5x difference on my Business Class Deluxe, and even farther than the 10x of Business Class Deluxe 100.

Please review the requirements for a valid answer: You must be of DrDrew's caliber or better. A reference to Wikipedia doesn't get you there. Thanks so much, again.


ExoticFish

join:2008-08-31
Stuarts Draft, VA

And an attitude like that won't get you anywhere.

The technology behind our cable connection is what's causing the speed limitation is what I believe tshirt was trying to get across. The hardware itself COULD easily work on a symmetrical platform, cable and modems. As far as the head end hardware goes I'm pretty sure it could also, with changes of course.

Also when you look at it I think companies assume customers don't need as much upload bandwidth as they do download, which for the most part I'd say is true.
--
»www.VAJeeps.com

Expand your moderator at work

bernardc

join:2009-12-13
Berkeley, CA
reply to ExoticFish

Re: [Speed] Download/upload ratio: Is it physics?

I'm looking for reliable, verifiable, solid information. If you don't have it, that's no problem. No one knows everything. I certainly don't, and that's why I'm asking. There's no need to reply if you don't have the answer the meets the needed specifications for rigor. I have no interest in offending anyone, really.



tshirt
Premium,MVM
join:2004-07-11
Snohomish, WA
kudos:4
Reviews:
·Comcast
reply to bernardc

said by bernardc:

You must be of DrDrew's caliber or better.

He won't talk to you, since you even SUGGESTED there MIGHT even be somone better.

Besides since you're in Berkeley, couldn't you just call Stanford.

bernardc

join:2009-12-13
Berkeley, CA

tshirt, I am so glad you have a sense of humor!!!

I really doubt anyone could be better than DrDrew.

Regarding Stanford, right! I heard they're the best and the brightest.



news

@videotron.ca

Before cable Internet, cable tv plant were one-way only, with RF amplifiers passing foward signals from 54 MHz to 550, 600 or 750 MHz depending of the cable plant. So they needed a 2-way plant for the Internet, they choose to pass the return data (from the customer to the cable headend) below 54 MHz, in the 5-42 MHz band, where there wasn't any tv channels . So the bandwith available isn't much, but anyway Internet was new, almost only downstream traffic... With time, they changed the upstream modulation from qpsk to 16qam and today some cable plant use 64 qam to be able to gain more speed and bandwith on upstream channels.

Today, catv manufacturers buid amplifiers with wider upstream band 5-55, 5-65 and 5-85 MHz, but most cable plant still only use 5-42 Mhz band.

»www.cedmagazine.com/articles/201···m-speeds



Caddyroger
Premium
join:2001-06-11
To the west
Reviews:
·Comcast
reply to bernardc

said by bernardc:

I'm looking for reliable, verifiable, solid information. If you don't have it, that's no problem. No one knows everything. I certainly don't, and that's why I'm asking. There's no need to reply if you don't have the answer the meets the needed specifications for rigor. I have no interest in offending anyone, really.

Then should list the thing that you looked. No one know that you all ready looked at Wikipedia.
--
Caddy


telcodad

join:2011-09-16
Lincroft, NJ
kudos:5

4 edits
reply to news

I'm not DrDrew either (and he and others more expert on this can correct/clarify what I say), and while "news @ videotron.ca" has touched on a lot of this already, here's my shot at this anyway:

The asymmetry between the much higher download speeds vs. the lower upload speeds is basically due to both the asymmetrical bandwidths and SNRs of the downstream (or "forward") path vs. the upstream (or "reverse") path.

Because of the original broadcast TV channel assignments in the US, the upstream path from the customer back to the cable headend has been limited to between 5 to 42 MHz (vs. bandwidths of 50 MHz or more that are currently being allocated to HSI service in the downstream).

This bandwidth-limited, low-frequency, upstream path is also susceptible to an number of impairments such as impulse noise, the "ingress" of interfering signals from outside the system (such as from CB and ham radio transmissions), and from noise and interference originating from inside subscribers' homes. This results in SNRs that are typically 6 dB or more worse than those obtained on the downstream path, so that only lower-order modulations that can tolerate the lower SNRs, like 16- or 64-QAM, can be used (vs. 256-QAM in the downstream).

Here are some recent threads in this forum that have discussed the limitations of the upstream path:
8 downstream 8 upstream modem? - »8 downstream 8 upstream modem?
4 Upstream Channels - »4 Upstream Channels

Here are also some other articles that discuss the issues with the upstream path and some things that can be done to reduce the asymmetry:
Why Is Cable's Upstream Path So Darned Ugly? - »www.translation-please.com/colum···umnid=97
Cable's Upstream Gap - »www.lightreading.com/blog.asp?bl···lr_cable
Will Anyone Switch On Cable's Upstream Booster - »www.lightreading.com/document.as···lr_cable

EDIT: BTW - Here are the other parts of Leslie Ellis's early articles about Cable's upstream path (and still fairly applicable for being over 10 years old!):
Peer-to-Peer Meets Cable's Upstream Path - »www.translation-please.com/colum···umnid=98
How Cable Gets More Stuff Upstream - »www.translation-please.com/colum···umnid=96