You can think of it in the bottom layers of the TCP/IP model (there's
a decent summery here: http://www.tcpipguide.com/free/
t_OSIReferenceModelLayers.htm). The TCP/IP layer model is a sort of
protocol/structure for sending data over the internet.

The first layer is the physical layer, litterly the ones and zeros on
a wire. How and what they are depends on the medium that they are
sent over. For intra-networks (like from your modem to your computer)
its on ethernet, or electrical pulses on 8 twisted coper wires. For
longer distance, it might be on a fiber optic wire, at which point it
is light pulses sent by lasers down a very clear and thin glass wire.
More advanced stuff includes wireless, where it is radio waves sent
from a base station through your head, or satellite, which is more
powerful energy bursts sent to a from a satellite in orbit. Since all
this data is digital, there are 2 states of the pulses: on and off.
Each pulse is one bit. That's basically how computers can talk to
each other.

But as you move up the TCP\IP chain, things get a bit more
complicated. The way described above is no different from a
telegraph, pluses down a wire. The thing that's amazing about TCP\IP
is that it puts bits together in a thing called a packet. The size of
the packet depends on what you're doing, but its usualy 64 bytes (or
512 bytes) of data. Surrounding this data is some meta-data the
records where the packet is going to and some quality control
information. This makes sure that if something disturbs the data in-
route (a 1 gets misinterpreted as a 0, a wire breaks along the way,
or any number of problems), the packet can get resent in its
entirety. This also means that long strings of data, like a MP3 or a
document, can get split up en-route, and 'routed' around trouble.
This takes places on levels 2-4 of the TCP/IP model.

For all intents and purposes, data travel down the wire is
instantaneous, it travels at the speed of light. All the delay is
added in by the routers, which have to read the packets and send them
to the right place, and the modems or NIC cards, which have to
produce the electric pulses to begin with.

It's been a while since my Cisco classes, so the details are most
likely wrong. Sorry if this doesn't answer your question, are you
looking for what physically happens to the pulses, or something else?
--------
Ben Spigel
Department of Geography
University of Toronto


On 28-May-05, at 3:24 PM, Sue Thomas wrote:

> I've been thinking about this a lot lately. Can anyone point me to
> research
> on the following question:
>
> If I throw a ball to you, we know that it passes through the air
> between us.
> (unless we are in a vacuum, in which case we would both be dead etc
> etc)
>
> Q: When a data packet 'travels' from one node to the next, does it
> pass
> through anything? What is between the nodes? I know transfer is
> very fast
> but nevertheless it is still transfer so there must be a point
> where it is
> in neither place so it must be somewhere else. Shouldn't it? Or have I
> misunderstood?
>
> All hypotheses welcome. Preferably those I can understand ;)
>
> Sue
>
> http://travelsinvirtuality.typepad.com
>