Re: use the outer edge of Eithernet

Matthew Beebe (msbeebe@mtu.edu)
Sat, 13 May 95 20:23:30 EDT


> From: Michael Sattler <msattler@jungle.com>
> Subject: Re: use the outer edge of Eithernet
>
> >"...No network bandwidth is used in transmitting the video. Hundreds of
> >simultaneous video calls can be made. Other DVC systems often have the
> >ability to connect within the building, but these systems use enormous
> >amounts of network bandwidth, rendering the network unusable for the people
> >who use the network when even one video call is in progress."
>
> I understand how having a processor and memory on a special card would free
> up the main CPU, but the bit about "no network bandwidth is used in
> transmitting the video" rings my bullshit bell, even if it "transmits video
> at broadband rates" (which I've never heard before).
>

Well, think of it as "out-of-band" and you'll be a step ahead.
The 802.3 (ethernet) only uses a certain portion of the physical
bandwith on the cable...

For instance.. (I'm smart about CATV, so I'll give specifics
from that area, but its the same concept).

On a cable TV wire, there is aprox 700Mhz of "bandwith" available
(the "pipe" is that wide). Each TV channel uses 6Mhz of bandwith,
thus a typical CATV system can transmit 100 or so channels...

The same thing is done with these video/voice over existing
systems. The data is modulated onto an unused "channel" of
the existing ethernet cable. ie: The 802.3 only takes a fixed
amount of bandwith to work.. the cable has physical characteristics
allowing it to carry more data.

> Video is bandwidth-intensive. If you're passing bits from one machine to
> another, it's using up bandwidth that could be used for, say, playing DOOM
> or Marathon. Someone hand me a clue if I'm missing one here, but this
> sounds like marketing hand-waving here.
>

The definition of bandwith is twofold. It has historically related to
the width of the frequency spectrum. Only recently has it become
synonymous with data through-put.

-Matt