[lug] linux router project
rm at mamma.varadinet.de
rm at mamma.varadinet.de
Wed Aug 23 13:44:46 MDT 2000
On Wed, Aug 23, 2000 at 12:50:37PM -0600, PC Drew wrote:
> "To understand recursion, we must first understand recursion."
> On Wed, 23 Aug 2000, Glenn Ashton wrote:
> > Perhaps their objections are real. 10base2 can be very flakey. Does
> > anyone else on the list know if the network people's objection to a media
> > converter is valid? I'd be curious to know.
> Out of pure ignorance, here's a question: why not upgrade to Ethernet? Granted,
> I don't know very much about token ring or any of these other topologies, but
> I do know ethernet. And I do know that it works, it's fast, and it's good.
> Do they not want to upgrade because it would cost too much money?
> If anyone can elighten me as to why 10base2 is better than ethernet, I'd appreciate
10base2 IS ethernet ;-)
The colloquial term ethernet stands for a whole family of both networking hardware
as well as network protocols (i.e. it stands for several related types of cabeling
and the lowlevel protocols run over these cables).
There are several types of cables used for ethernet:
- the old 'thick wire' coaxial cable (10base5, wasn't it). Impressive red cables
about a thumb thick, and a major pain to bend (i think the minimum bending
radius was 50 cm). You atached a node to the cable by actually drilling a hole
into the cable and sticking a connector into that hole (no joke!).
- the slightly newer 'thin wire' coax cable, traditionally yellow. This is the
10base2 cable. Like the thick wire this was a bus system (i.e. one long cable
with nodes atached to it. Terminators on both ends of the cable).
- 10baseT cable (twisted pair category 5 cable). This is the cheap ethernet you
probably know. On the cable-level this uses a star topology, but on higher levels
it still is a bus (all nodes 'see' all packets on the bus).
- 100baseT cable (very similar to 10baseT but much faster ...). Without going
into too much detail, there are some important differences between the last
two, so it's not too easy to build a box that converts from one to the other
(different binary encodings (i.e. the way the 'zeros' and 'ones' are represented
'on the wire', different frames etc.).
This is only the cable part: of course one can (and often does) run different
network protocols over the same wire. AppleTalk as well as TokenRing commonly
run on 10baseT (the hardware protocol is then called 'ethertalk'...).
What unifies the ethernet family then? It's the basic network concept behind
the different protocols: You send data frames (packets) as if the wire where
the radio ether (hence the name). Whenever one station wants to send it checks
if the 'ether' is free, and if so starts sending. If not, the station waits
for a while (the exact algorythm for this waiting is actually pretty tricky)
and tries to send again. As you can imagine, once the 'ether' starts getting
filled up, sending gets very hard (the number of unsucessfull sends increases
dramatically--the net is saturated). For ethernet, once you reach 60% saturation
the performance drops fast. This might result in certain nodes not being able
to send packets at a decent speed. In a TokenRing network the bandwidth is
split up evenly and there are no collisions. A 'token' is passed arround,
and whoever has the token is allowed to send (yes, i know, this is grossly
If you are interested in networking, there are of course a lot of good books
arround. If you don't want to (or can't) spend a lot of money you might try
the PDF book available online at:
(i just checked it, i think you now need to register ...)
I would suggest 'IP Network Design Guide'. I think this book gives you a
lot of valid information on networking (not only ethernet).
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