%-> Fine those are the technical details don't loose the overall
%-> picture. Sorry
%-> I should have been more rigerous with the details but I was
%-> just trying to
%-> show a concept. I was just trying to get it clear that the DSL
%-> represents
%-> the conection to the ISP. Not the gateway to the internet that
%-> is the ISP.

Well, no, DSL doesn't represent the connection to the ISP. It's the
connection to IPnet -- that's perhaps what you meant? And sorry, I didn't
mean to imply that you weren't being rigorous with details or anything :-).

%-> I was also noting that dial in modems have a need for a fixed
%-> continuious
%-> 64kb/s per modem (digital to analogue conversion) and require
%-> hardware to
%-> decode the modems signals. This represents costs in hardware
%-> and possible
%-> multiple "telco" circuits. This to me seems more expensive than
%-> having one
%-> central ATM portal which handles all the DSL connections with one router
%-> etc.

Upstream, 56Kbs modems are analogue so to speak, even the new V.92 ones, so
there's no conversion needed. The path to you is digital, however. Each
voice circuit is actually a digital 64Kbps one already, so apart from
equipment at the ISP end, there's not that much investment required to make
56K modems work over the Telecom network. (This is simplified of course.)

%-> Also Saying that DSL runs at 8 Mb/s is misleading. You need
%-> something at the
%-> other end which can serve 8MB/s. The rate at which the DSL runs
%-> has got an
%-> indirect link to the internet gateway. This is determined by
%-> the ISPs desire
%-> for quality of service. TCP/IP is packet based (atm more so) so that
%-> "streams" of packets can easily be interleaved spreading the
%-> badwidth across
%-> multiple clients. Just because you have a link to your ISP of
%-> 8MB/s does not
%-> mean that your link to the internet is 8Mb/s you share the link to the
%-> internet with other users.

No, it's not really misleading, but it's important to take into account what
the network itself can handle. Last time I checked, I got 420KByte/s per
single TCP session -- that's ~3.28Mbit/s. However, if you can aggregate your
TCP sessions, you can double that easily. I've done it with Mass
Downloader...

You might not be able to get e.g. 8Mbps out of a single server on the
Internet, but with that sort of bandwidth, you have enough headroom to open
up several connections to different servers, so your aggregate bandwidth
might get close to the max.

However, as you point out, it's not just that the speed of the DSL link that
decides what performance you'll get. There are many more factors, such as
traffic shaping by ISPs, etc.

Incidentally, ATM is quite different from TCP/IP, but that's probably
besides the point here.

%-> I also note that note everybody is constantly using all their bandwith.
%-> Usage is bursty - you download, you browse. So this means on
%-> average you may
%-> use alot less than your total available bandwith.

Yes, that's for sure. I don't think Telecom or anyone could support users
running at full tilt 24-by-7...

-- Juha

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Received on Fri Oct 6 12:09:08 2000