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Observer josesmn
Observer
8,287 Views
Registered: ‎07-29-2008

CRC of Jumbo Frames used in Gigabit Ethernet

does any body know how is the CRC of jumbo frames (in Gigabit Ethernet)of size greater than 9K is found? What algorithm is used for that?

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3 Replies
Xilinx Employee
Xilinx Employee
8,259 Views
Registered: ‎08-01-2007

Re: CRC of Jumbo Frames used in Gigabit Ethernet

Hello,

 

I believe CRC for jumbo frames is calculated the same way as a standard frame (CRC32).  Specifically, using the method described in sec 3.2.8 of IEEE 802.3-2002.  As paraphrased in UG194:

 

"The value of the FCS field is calculated over the destination address, source address,
length/type, data, and pad fields using a 32-bit Cyclic Redundancy Check (CRC), as
defined in IEEE Std 802.3-2002 para. 3.2.8:


G(x) = x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 + x2 + x1 + x0


The CRC bits are placed in the FCS field with the x31 term in the left-most bit of the first
byte, and the x0 term is the right-most bit of the last byte (i.e., the bits of the CRC are
transmitted in the order x31, x30,..., x1, x0)."

 

http://www.xilinx.com/support/documentation/user_guides/ug194.pdf

 

 

-Kyle 

 

 

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Visitor santosh321
Visitor
8,174 Views
Registered: ‎07-30-2008

Re: CRC of Jumbo Frames used in Gigabit Ethernet

hi,

 

It has been found in studies that the efficiency of CRC-32 remains same for frame sizes from 1500 to 9016 (approx). However, implementation of frame sizes bigger than this doesnt make sense, because the effciency of CRC-32 decreases and errors creep in. Hence, using conventional CRC-32 for frame sizes bigger than 9K wont work. 

 

So incase u are looking in terms of experimenting with jumbo frames greater than 9000 which is presently being pushed through, then u will also have to think in terms of implementing a bigger CRC-32 genrator polynomiial, for which yu will again voilate the frame format, which seems unlikely in near future.

 

regards

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Explorer
Explorer
6,980 Views
Registered: ‎10-01-2008

Re: CRC of Jumbo Frames used in Gigabit Ethernet

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