Clark Martin skrev:
>There seems to be a misunderstanding about how Ethernet works.
>Ethernet is described as CSMA/CD or Carrier Sense Media Access /
>Collision Detection. When two nodes attempt to talk at roughly the
>same time they both attempt to assert the media. The specifics of
>this depend somewhat on the media (10BaseT, 10Base2, 10Base5,
>10BaseF). If another device has already asserted the media the
>second one will back off and wait. This is the CSMA part. In a
>normal network there is only a very short period of time in which two
>devices can both assert the media and both think they have it. In
>this condition they both then try to send data which causes a
>collision and both then quit and wait a random amount of time to
>retry. This is the CD part. Because of this collisions SHOULD be
>rare. In a well configured network they are.
I'm quite aware of how CSMA/CD works, but I didn't want to delve any deeper
when trying to make as simple an explanation as possible.
Still, what configuration could minimise collisions? I get collision even
while FTPing between two nodes on my private network. The very nature of a
CSMA/CD network leads to collisions.
>This short period of time is dependent on the time it takes for a
>signal to go from one end of the system to the other. This is both
>the propagation time through the cable and through any hubs. If the
>network has troubles such as too many hubs, over long cables or
>excessive noise collisions can happen more than they should.
Well, yes, cable length should matter. The maximum legal length of an Ethernet
is 50 ms (milliseconds, not metres) from one end to another. Still, during
those 50 ms, downstream nodes may think that the ether is free, and start to
transmit as well. Since clairvoyance is not part of any current Ethernet
standard, collisions is something we have to live with.
>>The larger your networks grows, the more simultaneous traffic, and the more
>>collisions. Sooner or later, those collisions will have a serious impact on
>>your throughput, and you may feel as though you're on a two-megabit network
>>instead of a ten-megabit one. This is the idal application for a switch.
>Switches break collision domains, i.e. collision related problems on
>one leg of a switch do not cause collision problems on any other.
>Switches can mask network problems. This is good and bad. It's good
>because often the problem remains small and may not be noticeable.
>It's bad because it makes it harder to locate problems which may
>later come back to bite you.
It's bad because you can't run a sniffer. =)
If you don't like the collisions, though, you're better off running Tokenring.
--
En ligne avec Thor 2.6a.
The generation of random numbers is too important to be left to chance.
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