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    New iFCP draft



    With regards to the new iFCP draft
    
    5.3        Trailing iFCP CRC
    
        This original Fibre Channel CRC shall not be encapsulated into the
        iFCP message.  Rather, iFCP MAY use a 32-bit field containing a CRC
        calculated over the data contained in the frame from the iFCP
        AUGMENTED DATA to the iFCP Payload (inclusive).  This includes the
        Fibre Channel header and payload.  The iFCP CRC follows the iFCP
        payload, and the CRC algorithm is the same used for the Frame Check
        Sequence (FCS) of IEEE 802.3 Ethernet frames.  A bit in the iFCP
        FLAGS field in the iFCP header indicates the presence or absence of
        this 32-bit trailing CRC. 
    
    I would suggest "Rather, iFCP MUST use a 32-bit field containing a CRC ..."
    unless ethernet provides an equivalent CRC elsewhere.  The reason is that I
    believe gigabit ethernet uses the same physical layer as fibre channel.
    This physical layer is specified for fibre channel to have a data bit loss
    rate of 1 in 10^12 or less, and is not "perfect".  I think the CRC is
    designed to throw out these imperfect frames instead of resulting in data
    corruption.  Without the CRC, physical layer imperfections within
    fibre-channel specificaiton may lead to data corruption.
    
    Also, I am not intending to show preference for iSCSI or iFCP with this
    email.  I just was skimming over the standard and thought this feedback
    might be helpful.
    
    Stephen Elliott
     
    


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Last updated: Tue Sep 04 01:05:53 2001
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