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    RE: new iSCSI draft - 02.txt



    The problem is: at that layer there is simply not a byte stream. The data
    is contained in socket buffers which are most likely mbuf clusters for most
    implementations. To "simply insert a few extra bytes" requires mbuf
    manipulation.
    Mbuf manipulation can processing intensive. Depending on how the mbuf data
    is
    packaged a small DMA operation may occur for these few extra bytes also.
    Dave
    
    -----Original Message-----
    From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
    Matt Wakeley
    Sent: Wednesday, January 03, 2001 7:21 PM
    To: IPS Reflector
    Subject: Re: new iSCSI draft - 02.txt
    
    
    David Peterson wrote:
    >
    > I believe there was agreement to remove the Urgent-Pointer framing
    mechanism
    > but don't recall any agreement to replace it with an in-stream marker. For
    a
    > software implementation it would be hard to support this type of framing
    > mechanism. I believe a TCP option indicating the message boundry or a
    > fixed-length PDU at a granularity to minimize overhead are much better
    > solutions and are workable for both software and hardware implementations.
    I
    > have not seen an agenda but I would hope this issue would be discussed at
    > the upcoming meeting in Orlando.
    > Dave
    
    What is so difficult for software to insert a few extra bytes in the byte
    stream?  It's simply a layering problem:
    
    iSCSI layer <-> marker layer <-> TCP
    
    Normally, the marker layer simply transfers the bytes from the iSCSI layer
    to
    the TCP. Every X number of bytes, the marker layer inserts the marker into
    the
    byte stream.
    
    Since your software will probably not benefit from the receipt of the
    markers,
    it would negotiate not to receive the markers.  It would only send markers
    *IF* the remote node requested them to be sent.
    
    -Matt Wakeley
    Agilent Technologies
    
    


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Last updated: Tue Sep 04 01:05:58 2001
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