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    RE: FCIP: A question about framing



    Doug:
    
    These codes were derived from an early implementation of a Fibre Channel
    Chip.
    There is no algorithm involved as far as I know in creating these
    byte-encoded
    codes.
    
    On the alignement point,I was refering FC standards which like to align on
    word
    boundaries. We picked these codes from FC-BB and would like to adhere to
    similar
    mapping the FC Frames both in IETF and FC-BB2. Beyound that there is no
    other
    reason to use 4-bytes.
    
    Hope this historical commentary clears the reasons for 4-bytes of SOF/EOF.
    
    -Murali
    
    -----Original Message-----
    From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
    Douglas Otis
    Sent: Wednesday, November 01, 2000 5:34 PM
    To: Murali Rajagopal; Merhar, Milan; ips@ece.cmu.edu
    Subject: RE: FCIP: A question about framing
    
    
    Murali,
    
    I fully understand a need for alignment.  TCP however will not provide any
    alignment!  With respect to the FC frame bytes, an encapsulation process
    could easily move both SOF and EOF into a prefix to aid in processing these
    bytes.  This prefix could include a timestamp as well.  Do you know the
    algorithm for creating these byte codes?  For alignment, you should review
    RFC 2960.
    
    You can see an example at:
    http://search.ietf.org/internet-drafts/draft-otis-fc-sctp-ip-01.txt
    
    Doug
    
    > Doug/Milan:
    >
    > Although there are 4 bytes specified, only a single byte is really used.
    > The reason for using 4 bytes instead of one was word boundary alignement
    > previously discussed in FC-BB T11 WG.
    >
    > Hope this helps.
    >
    > Murali Rajagopal
    >
    > -----Original Message-----
    > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
    > Merhar, Milan
    > Sent: Wednesday, November 01, 2000 10:11 AM
    > To: ips@ece.cmu.edu
    > Subject: FCIP: A question about framing
    >
    >
    > I was pleased to see the new draft for FC over IP
    > ( draft-ietf-ips-fcovertcpip-00.txt ) but something
    > in it left me a bit puzzled.
    >
    > The encapsulation that is described envelops the
    > entire FC frame, including its SOF and EOF delimiters,
    > and then transports it over TCP.  The draft correctly
    > points out that in FC the SOF and EOF sequences
    > are encoded at the 8b10b level starting with a "comma"
    > character, which is a reserved 10-bit code, which does not
    > correspond to any 8 bit value.  But, it then says
    > that SOF and EOF are encoded in TCP as 4 byte sequences.
    >
    > This is where I get confused.  Don't you then have to
    > prohibit the appearance of the SOF and EOF sequences
    > (which are now just a set of four regular bytes)
    > in the normal payload stream, using a processing-intensive
    > technique like escape sequence insertion, etc?
    >
    > The only other alternative that comes to mind is to use
    > the presence of a valid CRC as a gate to on accepting an EOF
    > sequence.  And that, I believe, is patented technology.
    >
    > - milan
    >
    
    
    


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Last updated: Tue Sep 04 01:06:32 2001
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