At 11:31 PM 2/8/01, Jeremy Dumoit wrote:
> I think I'm unclear on some of the protocols here... for what purpose
>would a protocol detect errors, but not correct them?
A protocol detects errors so it can throw a bad frame out rather than pass
it to the next layer up. Most data-link-layer protocols have a CRC that
does error detection. The sender adds up all the bits and does some bizarre
calculation on them. The sender places the result in the CRC field of the
frame. The receiver does the exact same algorithm. If the result is
different than the CRC in the frame, the recipient throws out the frame.
IP also has a checksum. If the frame arrives OK but gets damaged before IP
gets it, then IP throws it out. How could that happen, you may wonder?
Software bugs, memory overflows, other bad things like that. TCP also has a
similar checksum for the same sorts of reasons.
Hope that helps. There's no such thing as a dumb question. Seriously. No
matter what you ask to this group, there will be lots of useful answers
(and some not so useful answers. &;-)
Priscilla
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Priscilla Oppenheimer
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