[MLB-WIRELESS] Cat5 max length

[Donovan Baarda]

On Thu, 2003-01-23 at 22:56, Peter Hall wrote:
> 
> ----- Original Message -----
> From: "Tony Langdon, VK3JED" <vk3jed at optushome.com.au>
> To: "Joe Hovel" <joe.hovel at med.monash.edu.au>;
> <melbwireless at wireless.org.au>
> Sent: Thursday, January 23, 2003 10:38 PM
> Subject: Re: [MLB-WIRELESS] Cat5 max length
> 
> 
> > At 10:29 PM 23/01/2003 +1100, Joe Hovel wrote:
> >
> > >Can someone remind me what the maximum length for cat5 is? Also need to
> > >know if a switch or hub can act as a repeater to extend the distanc.
> > >Cheers,
> >
> > Max length is 100m.
> >
> > A switch can be used to get more distance (separates collision domains),
> > but a hub can't.  I've actually proven this in practice. :)
> >
> > 73 de Tony, VK3JED
> > http://vkradio.com
> >
> >
> > To unsubscribe: send mail to majordomo at wireless.org.au
> > with "unsubscribe melbwireless" in the body of the message
> >
> How does collision domains have to do with distance?
> and why not a hub, after all it is a multi port repeater...? and they
> regenerate and retime the signal (presuming its powered of course)

I'm sure someone else can probably answer this better than me, but it's
to do with collision detection. I'm not 100% sure that all hubs actually
do regenerate and retime the signal, but in any case the problem is not
signal degradation.

The longest propagation time must be less than the packet transmission
time, otherwise you can't guarantee that collisions can be detected.

I believe this is the reason 100Mbps has a shorter range than 10Mbps,
and 1Gbps relies on jumbo-packet sizes to get anywhere at all.

example; nodes A and B are at extreme ends of an ethernet segment. Both
nodes start transmitting at the same time to node C in the middle. To
detect if there is a collision, they both listen at the same time as
transmitting. If both nodes finish transmitting their packets before the
start of the packet reaches the other end, neither of them see a
collision and think the packets were successfully transmitted. Meanwhile
node C in the middle gets garbage.

A switch handles the collision resolution, so each connection to a hub
behaves as a separate ethernet segment as far as collision resolution is
concerned.

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