At 1:22 AM +0100 7/11/01, Iggy Drougge wrote:
>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.
50 mS (.05 S)???. That's a cable length of something around 10,000
Km. Propagation time for 100 m of cable is around .5 uS. A network
could have up to 5 cable segments for a total of 2.5 uS. I don't
know what the maximum delay through a hub is though so I couldn't
give a number for the total time.
At my daughters' school they were getting regular collision traffic.
This is on a 200 node network with maybe 50 connections to the main
hub. That collision lights on that hub were lighting up pretty
steady. Eventually the problem was isolated to an over length
connection to a remote hub. A switch was placed on that connection
to isolate it and to extend the working length of that leg. With
that change the collision lights went out. Only sporadic blinks of
the collision lights happened after that.
> >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.
I can't imagine anyone today selecting tokenring if they didn't have
to. While it has some nice technical advantages like so many
computer ideas market pressures are making it passe.
--
Clark Martin
Macintosh Consultant
Another designated driver on the Information Super Highway
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