[thelist] cable modem bandwidth

Daniel J. Cody djc at five2one.org
Tue Sep 12 21:40:17 CDT 2000

Oliver Lineham wrote:
> At 12:56 12/09/00 -0500, you wrote:
>> Part of the idea that cable modems will get slower with more and more
>> people in the 'hood using them is true, part isn't.
> Wow, dan, that was a great explanation of things - thanks!
you're welcome, I'm glad so many enjoyed it.. when i get some time, i'll 
edit, format, and post it on the evolt website..
> One remaining question I have is, how do upstream speeds compare?  I 
> know the cable modem speed is set by the cable company - eg you might 
> only get 512kbps upstream although the modem is capable of 2mbps.  
> Obviously both DSL and Cable have more capacity downstream than 
> upstream, but which is better in that respect?
Good question. Lets take a look at DSL uploads first. DSL is a generic 
term that encompasses a variety of technologies. Each of these 
technologies is somewhat the same, but also different in how it can 
compress data. Compressing the data to send over you're phone line 
allows you to have faster speeds.. The better the compression, the 
faster uploads you'll have. The difference between an analog modem(at 
56K or 33.6K or 28.8K like many have) and a DSL modem isn't much, but at 
the same time alot.

Don't know when I became the DSL expert here ;) anyways..

An analog modem is so 'slow' because it only uses a small portion of the 
available amount of information that could  be transmitted over copper 
wires(your phone line), the maximum amount of data that you can  receive 
using ordinary modems is about 56 K(the fastest modem currently). The 
amount you can download is limited by the  fact that the telephone co. 
filters information that arrives as digital data, puts it into analog 
form for your telephone line, and requires your  modem to change it back 
into digital.  Basically, its dumb and ineffcient.

The reasons DSL is so fast over the same wires as an analog modem is 
digital data(DSL) doesn't need to be changed into analog form and back, 
like an analog modem does. Data is transmitted to you from the phone 
company in pure digital form, letting them use more of the 'pipe' that 
your phone lines offer. Christ, i'm getting of on a tangent here again 
so I'll cut to the chase :)

Here are some of the 'flavors'(different compression techniques) of DSL:

ADSL: Asymmetric Digital Subscriber Line - the most common form of DSL. 
Allows for good download speeds, but upload speeds are limited because 
most  is devoted to the downstream direction. For the majority of web 
users, this is great, because they don't spend a lot of time uploading 
data. Typically you'll see 1.5Mbps at 18,000 feet; 2Mbps at 16,000 feet; 
6Mpbs at 12,000 feet; 8.5Mbps at 9,000 feet from the phone company 
download speeds. You'll see from anywhere between 16 and 640Kps upload 
speeds, depending on distance from the phone company(and therefore 
signal degridation)

HDSL: High Bit-Rate Digital Subscriber Line - oldest form of DSL. It 
allows for equal upload and download speeds, although it sacrificies(i'm 
not a f-ing spelling bee contestant obviously :) overall speed to 
achieve equal upload and downloads.

SDSL : Symmetric Digital Subscriber Line - almost the same as HDSL but 
much faster. Can carry a full t-1 speed(1.54Mps) in full duplex(both 
upstream(upload) and downstream(download)). You have to be pretty damn 
close to the telephone company(or one of their switches) to get this 
though, because the signal degrades in a hurry.

VDSL: Very HighDateRate Digital Subscriber Line - if you're within 
spitting distance of you're phone company, this is the fastest option 
you can have. You can typically get 55Mps with VDSL's compression 
algorithms. The tradeoff is that you have to be within 800 feet(i dont 
know how many meters that is :) of the phone company.

There are a number of other compression algorithms out there that add to 
the alphabet soup, but those above are the most common. And as my 
previous post mentioned, this is between you and the phone company, 
*not* between you and the internet.

So to answer you're question onlineham ;) - your upload speed depends on 
what compression technique you're using, which is directly correlated to 
how close you are to the phone company. You *can* get as high as 55Mps. 
The common user however is somewhere between 128Kps and 540Kps  for 
upload speeds. A typical cable modem user(myself with time warner) can 
achiever much higher or lower as well. I can upload to my servers at 
work at about 1.2Mps in an off-peak time. Naturally, congestion can 
lower that(or a DSL line) down to what I used to use for a modem when I 
had an Apple ][gs :) (my favorite computer of all time still btw)

Hope that answered your question and cleared up some of the confusion 
about DSL. Guess I'll have to put this into my other post and make an 
article out of it :) Thats cool though, we all know that people who put 
their good posts from thelist( 
http://evolt.org/index.cfm?menu=8&cid=3093&catid=18 ) on the evolt 
website are bound to become cult icons of sexy geekiry like our own sgd :)


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