Re: wireless lans with multiple accesspoints

Peter,

I don't think freebsd-mobile is the place for Ethernet tutorials, but
this is getting annoying. For those actually interested in mobile
issues, DELETE now.

In all forms of Ethernet collision detection is a local activity. Each
interface MAC detects collision on its own and notifies the local
system. End of story.

All modern (non-coaxial) flavors of Ethernet detect collisions by the
trivial technique of seeing the receive and transmit lines active at
the same time. It's really pretty simple. 

If transmit is active and receive becomes active during the
transmission, declare a collision. There are many expansions on
this, but this basic situation is ALWAYS the case.

Running full-duplex does two things:
Don't check on whether receive is active before starting a
transmission and don't do anything when it becomes active.

If an interface is in full-duplex mode and detects a collision, it IS
broken as per both the spec and reality. 

I don't think you are lying, but I know that you are wrong. Either
something was broken or the thing you saw as a collision was actually
a "hold-off" message from a switch that some dumb piece of firmware or
software calls a collision. I suspect that this is the the most likely
explanation and fits my never having seen it since I use equipment
from a fairly small set of vendors.

R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: [email protected]			Phone: +1 510 486-8634

To Unsubscribe: send mail to [email protected]
with "unsubscribe freebsd-mobile" in the body of the message