5000' ethernet?

David Kelly dkelly at hiwaay.net
Thu Jul 16 04:22:21 UTC 2009

On Jul 15, 2009, at 5:41 PM, Michael Powell wrote:

> David Kelly wrote:
>> Not directly FreeBSD related, but how much of a chance is there  
>> that two
>> machines could communicate directly over 5,000 feet of cat5 with no
>> special hardware?
>> IIRC the classic ethernet problem limiting the distance between the
>> farthest points on a network had to do with timing and collisions. If
>> these two NICs are configured full duplex then it seems one would  
>> have
>> no idea how far away the other was due to timing issues.
> No. Ethernet uses a protocol design called Carrier Sense Multiple  
> Access
> with Collision Detect, or CSMA/CD. The maximum lengths are indeed  
> related to
> timing and the timing is a direct result of the propagation delay  
> in the
> medium. The velocity factor will be some percentage of the speed of  
> light.

Since when does one have CSMA/CD when configured as full duplex? All  
full duplex ethernet connections are point to point, machine to  
machine, or machine to switch. There is no multiple access on full  
duplex. No chance of collision.

So I'm thinking at 5,000' the problem is one of echo cancelation and  
signal loss, not one of ethernet protocol.

David Kelly N4HHE, dkelly at HiWAAY.net
Whom computers would destroy, they must first drive mad.

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