In article <fjgldq$1fam$(E-Mail Removed)>,
Andy <andy-(E-Mail Removed)> wrote:
>Weird request I guess.
>
>I have a classroom and access to an ethernet socket on the wall.
>
>I would like each student to have their own DSL line to
>their desk so they can install and configure their own DSL
>modem pci card. Then ideally go through the rest of the
>course using that as their internet connection for
>downloading software.
Assuming you mean ADSL, this requires different equipment at each end
of the wire pair. It isn't possible to operate a pair of normal,
consumer-type ADSL modems back-to-back.
Some "SDSL" standards do allow point-to-point use over a try pair.
SDSL needs a different type of modem, which tends to be more
expensive and harder to find.
>Since they would (or should) all be downloading the same
>software, a web cache machine could be placed at the
>ethernet connection.
>
>I never get to see this side of the ADSL hardware. It all
>happens back at the local telephone exchange, but this is
>what I'd like to achieve.
The device on the telco side is called a "DSLAM" (DSL Access
Multiplexer). This contains a number of individual modems, designed
to operate on frequencies complementary to the user's side --
transmitting on its receive channel, and vice versa (there are more
subtle differences also... e.g. modems at each end play different
roles during the "sync up" process.
Most DSLAMs gather traffic from the individual modems onto a DS-3
port, running ATM encapsulation. You then have to feed this into an
ATM-capable router, which can break out the individual PVCs (virtual
circuits) and extract the IP data payload from each.
Both pieces of equipment tend to be expensive, since only telcos and
ISPs buy them, and they can be difficult to set up. You might check
eBay for used gear.
There's such a thing as an "IP DSLAM", relatively new, which combines
both units into one, stripping off the ATM layer internally, and
giving you plain Ethernet on the uplink side (no DS-3).
>It easy enough to turn a linux beige-box into an ethernet
>switch, and I would like to think I could do the same but
>with DSL modem cards instead of ethernet cards, but I need
>pointers so some software here.
Why do you want to use DSL? As compared to plain Ethernet, its added
complexity (allowing for longer distances, and data transport over
wiring never designed for such, while sharing a loop with voice) would
be mostly wasted in your enviroment.
If you only want to restrict per-user bandwidth, there are several
ways of doing that entirely in software over normal Ethernet.
>What problems can anyone forsee?
>
>Cheers
>Andy Richardson
--
Jordan.
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