5000' ethernet?

Lowell Gilbert freebsd-questions-local at be-well.ilk.org
Thu Jul 16 15:32:07 UTC 2009

Michael Powell <nightrecon at verizon.net> writes:

> You are running Ethernet, right? CSMA/CD is part of the Ethernet framing 
> protocol. It is present in the protocol independent of simplex/duplex, etc. 
> As such the timing windows contain non-infinite discreet value ranges. It is 
> integral to Ethernet and does not get 'switched off' or disappear just 
> because a link is full-duplex. 

I call your attention to the specification (IEEE 802.3) for Ethernet:

1.1.1 Basic concepts
    This standard provides for two distinct modes of operation: half duplex
    and full duplex. A given IEEE 802.3 instantiation operates in either
    half or full duplex mode at any one time. The term CSMA/CD MAC is used
    throughout this standard synonymously with 802.3 MAC, and may represent
    an instance of either a half duplex or full duplex mode data terminal
    equipment (DTE), even though full duplex mode DTEs do not implement the
    CSMA/CD algorithms traditionally used to arbitrate access to
    shared-media LANs.

Lowell Gilbert, embedded/networking software engineer, Boston area

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