Date: Thu, 20 Jun 2002 07:38:58 -0700 From: "Kevin Oberman" <oberman@es.net> To: freebsd-mobile@freebsd.org Subject: Re: wireless lans with multiple accesspoints Message-ID: <20020620143858.B49335D04@ptavv.es.net> In-Reply-To: Your message of "Wed, 19 Jun 2002 13:10:15 EDT." <20020619171015.GH23903@pir.net>
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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: oberman@es.net Phone: +1 510 486-8634 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-mobile" in the body of the message
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