28 Jan
2008
28 Jan
'08
9:04 p.m.
It was thus said that the Great Jim Brain once stated:
Well, how does A know that its neighbor B is up? Just how many wires go
between A and B?
-spc (From the sound of it, it sounds like the answer is "one" ... )
Sean Conner wrote:
Since each computer is connected to two others, you end up with a ring
configuration (small example here):
A -- B -- C -- D
| |
E L
| |
F K
| |
G -- H -- I -- J
What I meant was that if A could transmit and receive from B and E at the
same time, then no tokens (more on that in a bit) are needed. Say, A wants
to talk to D; to do so, it needs to send a packet to B, which will then
forward it to C, which will forward it to D. Since the links are
bidirectional (in this hypothetical situation) A can talk to B or E at any
time.
If the links are unidirectional, then there has to be some way for A to
signal B that it has a packet to send its way---that is, if B isn't already
sending a packet to A. But first, you need to solve this situation:
A -- B
(a very simple network). A and B want to send each other a packet, at the
same time. How is this resolved? How you resolve this dictates the final
format of your protocol.
Each computer has two serial connections. Can
you send and receive on a
single "port" at the same time? Can you send and receive on both
"ports"
at
the same time? The design of the protocol depends somewhat upon the
The sync ports are unidirectional, but they can be run together, so an
SPI-like bus could be created.
capabilities of the ports. If you can't, then
you might want something
like
token ring, where a "transmit" token is passed around, and any computer
with
the "token" can transmit. If you can send/receive without problems on
either port, then just let the computers transmit at will.
On the latter, I don't understand. Who would they transmit to? How
would I deal with collisions? About the
only real problem to come up is configuration---how does each
computer get its address on the network? Manual configuration?
Automatic?
I cna hard code the addresses, but how does the ring/bus know when a
machine is alive, etc.