Unlike a store-and-forward switch, a cut-through switch will not hold onto
the frame while calculating the checksum. The frame will pass through the
switch--bad or not.
A CRC checksum cannot be calculated on the first X-bits of the frame. A
checksum is performed to determine if that value agrees with the value
contained in the frame received. Since the original CRC references the
length of the frame, it would be impossible to compute a CRC checksum on a
portion of the frame to determine its validity.
Hope that helps explain things (but I think Howard and Peter did a good job
already).
-- Leigh Anne
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Phil Barker
Sent: Friday, August 17, 2001 4:40 AM
To: [EMAIL PROTECTED]
Subject: Certificationzone White Paper ? [7:16354]
Just reading "Layer 2 Switching and Bridging" by Leigh
Anne Chisholm.
Cut-Through
"Since the port does not wait to receive the CRC at
the end 'if/of' the frame, it cannot determine the
integrity of the data received"
Happy with that.
"Cut-through switches CAN perform a CRC check as the
frame passes through the switch, keeping track of the
number of bad frames the port receives".
I'm Confused.
I'm guessing that some form of CRC checksum can be
calculated on the first X-bits of the frame before the
cut-through process is allowed rather than the entire
frame.
Any ideas ?
Phil.
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