RE: FCIP: A question about framing

["Douglas Otis" <dotis@sanlight.net>]

Murali,

Thanks for the history lesson.  Is there a reason for not moving SOF and EOF
to a prefix rather than placed within two 32 bit fields positioned at both
at the beginning and end?  The end field will not be as easy to find as a
prefix would be.  Is this design based on this historic chip.  Do you have
any specification for this chip?

Doug

> 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
> >
>
>