RE: Off topic - personal problem in VT

...but then we all realized that this is a point to point ethernet link
in full duplex, so it really doesn't matter much.

 

> -----Original Message-----
> From: [email protected] 
> [mailto:[email protected]] On Behalf Of Jim Thompson
> Sent: Wednesday, January 26, 2005 2:57 PM
> To: SeattleWireless Talk List
> Subject: Re: Off topic - personal problem in VT
> 
> Fred Weston wrote:
> > Jim Thompson wrote:
> > 
> >> 100m (328') is the "textbook" max length of Ethernet, but 
> this has a 
> >> lot more to do with signaling collisions than the ability to 
> >> correctly drive signals on the wire.
> >>
> >> Put a switch (or full-duplex adapter) on each end, and 
> "collisions" 
> >> become impossible.
> > 
> > 
> > That's interesting.  So you're basically saying that if you 
> eliminate 
> > the possibility of collisions on the wire, you can run 
> ethernet much 
> > further than 100 meters?
> 
> The collision domain is where the 100m "limit" comes from.
> 
> The smallest Ethernet frame is 64 bytes, or 512 bits.
> A 10Mbps system running over copper wire will carry bits at 0.75c, or
> 224,844 kilometers per second. This means that 256bits at 
> 10Mbps will be contained in 5,756 m of copper cable. The 
> original DIX Ethernet design specifications allowed for a 
> total of three 500m runs of copper cable, plus allowance for 
> 2 repeaters, and a generous allowance for error.
> 
> Getting 100Mbps Ethernet to run over twisted pair beyond 100m 
> is going to be much tougher than it will be @ 10Mbps.
> 
>  > Do you have any idea what the max
> > "transmission" length is?
> 
> It depends on the PHYs at both ends, and how good the wire 
> is.  AMD sold "extended distance" PHYs for a while.  Someone 
> else did too, and I forget the manufacturer.  When I was 
> engineering "Everywire" for Wayport, I speced extended reach 
> PHYs for the four uplink ports out of 
> each unit, just so we could cross a hotel if needed.   I saw 
> those run 
> 150m on  cat5.  Its unlikely that you can find these anymore.
> 
> I've seen low-attenuation cable marketed, with claims for 
> 160m.  I have no experience with this though.
> 
> Jim
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