Re: CRC of an out-of-order arrival data.

The issue is system need buffer arrival data until they were all
received since they could come out-of-order, even it is rare as you
mention. Then system need read them out to verify CRC, which took
memory bandwith too.

It will be great if storage system only save each packet's contribution
to the final CRC and commit this packet's data immediately. Util all
packets were received, verify over all CRC. No intermediate buffer for
data in this approcah. This is the point.






Maxim S. Shatskih wrote:
> Out of order arrival is usually a sign of a packet being lost, which is -
> in TCP - usually due to congestion on the router. Such things are very rare on
> iSCSI.
>
> --
> Maxim Shatskih, Windows DDK MVP
> StorageCraft Corporation
> maxim@xxxxxxxxxxxxxxxx
> http://www.storagecraft.com
>
> "alpha" <zhg.liu@xxxxxxxxx> wrote in message
> news:1124150106.352296.268030@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > Hi;
> >
> > I figured out a method to calculate accumulated CRC of data when its
> > packet arrival is out of order without large intermediate data buffer.
> > In aother word, I can calculate each packet's contribution to the final
> > CRC using each packet's CRC which could be give by hardware or protocal
> > chip. The overhead is little and the complexity is O(N), where N is the
> > packet number. By this method, what ever implemented in software or
> > hardware, it can potentially save lot of buffer space, CRC engine and
> > huge memory bandwidth. I thought iSCSI storage system could be a ideal
> > application candidate. I do not know if this one has some real value or
> > be implemented alreday. Any comment or feedback is welcome!
> >

.

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