frank wrote:
>
> The following is cut from a CCNA book:
> "FragmentFree is a modified form of cut-through switching ,in which
> the switch waits for the collision window (64 bytes) to pass before
> forwarding. If a packet has an error ,it almost always occurs
> within the first 64 bytes."
>
> I want to know how the last sentence is concluded?
> Any help would be appreciated.
Without going into gory details, 64 bytes is the frame propagation time
over a maximum length segment of the prefix of the frame. If a
collision occurs after the first 64 bytes, it is a "late collision"
in that by definition, if the network is to IEEE specifications, you
should be able to detect a collision within the first 64 bytes. The
"fragment free" avoids runts generated from collisions and the
associated jam packets generated when a collision is detected so that
they are not propagated.
However, fragment free does nothing to check the IP CRC or TCP checksum
(really only the former is relevant to a switch) so late collisions and
CRC errors can still be propagated.
Jeff Kell <[EMAIL PROTECTED]>
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