Re: [TCLUG:1649] couple of ???

[Ben Kochie <ben@nerp.net>]

you are confusing local connection to remote connection

when you connect to an internet site.. you are reciving info from a remote
server.. ok.. i'm going to do some technal explanations here.

here is how 56k works.

your ISP has a special kind of modem that can not be pluged into a normal
phone-line.  it usually comes in a rack-mount case, that has several dozen
modems in it.  this rackmount case has a single phone line connector that you
plug a T1 (one special kind of T1) line into.  the box also connects either via
serial ports to a terminal server, or via an ethernet cable to the ISP's
network.  these modems communicate digitally to the phone company network. 
just about every phone-line in minnesota is connected to a digital switch..
meening that the only analog voice link is from your phone to the local phone
switch.. (usually less than 5 miles.. and if you want DSL.. less than 2 miles)
from there it's converted to a stream of digital packets.. (similar to.. but
not really like real-audio)  the phone company runs a digital connection from
that switch to another switch, say.. in downtown mpls.. where it is sent out to
another digital switch at your ISP.. where it's fed strait into the 56K modems.
no analog conversions. :)  the fact that the ISP has no analog link to the
phone network meens it can transmit a higher quality audio signal.. but since
you have an analog phone line.. you can't send that quality signal.. the higer
the quality signal, the faster you can xmit data.

cable modems are a bit different.. the cable modem uses two totaly different
types of transport to upload and download data to your computer... but the
communication to and from your computer to the cable box is done via ethernet.

the cable box recives data from the same line as your cable TV.. you basically
put a splitter in, and run one end to your normal cable box, and the other end
to your cable modem (with a filter to make sure the cablemodem data doesn't
show up on your TV.. :)  if you think about how big an mpeg movie is.. and
think about how big a mpeg movie would be uncompressed.. then you know how much
data you can send down a cable line. but the problem is that #1.. everyone sees
the same data coming down the cable line.. since cable is basically like
screaming into a bunch of pipes.. everyone at each end of the pipe hears you.
and #2... for long distance runs.. they install repeaters.. and these repeaters
only repeat download.. no way to send a signal back up.  so they have to use
another connection to send the computers upload info.. so they use a modem.
this causes trouble for lots of things.. makes routing very wierd.. 



On 07-Oct-98 Ben Luey wrote:
> The cable modem question, reminds me of another question. How can a cable
> modem have different download and upload speeds. Isn't a download on one
> end an upload on the other end, and since data sent=data received,
> uploading should be the same as downloading. The same problem baffles me
> with 56k modems.
> 
> Thanks,
> 
> Ben
> 
> 
>> Ok I have been lurking enough....
>> 
>>    I am the network manager for a small ISP that is all Linux, right now we
>> have a mail server that also works as our main DNS service that seems to be
>> getting slow lately, of course I don't ever see it but some of my customers
>> do.  What I am looking for is a simple program that logs system stats like
>> CPU usage MEM usage both real and swap, and Disk space.  I have seen a few
>> programs but they all need X and I want something I can run in text.
>>   Next question, I am looking at getting a cable modem with MediaOne
>> Express, anybody done this yet? I don't like the fact that it is 1.5Mps
>> down and only 33.6Kps up but other then that what is the feel?  I am also
>> planning on making a Linux box for Masqurading IP's for my home network
>> when I get this too.
>> 
>> TIA
>> 
>> Jon Kotek
>> Online Advantage
>> 
>> 
>> 
>> 
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Thank You,
        Ben Kochie (ben@nerp.net)

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