RE: ISCSI: Urgent Flag requirement violates TCP.

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

Y.P.

> > -----Original Message-----
> > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
> > Silvano Gai
> >
> > >For example, if the following iSCSI messages are sent:
> > >
> > >Command A sent to target  ->
> > >Command B sent to target  ->
> > ><- target sends data/status for command A
> > ><- target sends data/status for command B
> >
> > In the previous example, if Command A and Command B are
> > transmitted in the same segment, do you care to specify if the
> > urgent pointer points to the first or second command?
>
> Always points to the first.

Unless you wait for each PDU to be acknowledged before sending the next,
there would not be a practical means to assure a pointer within the TCP
segment even if there were dozens of PDUs contained.  For your TOE to work,
extensive logging of possible PDUs would be required where each could skew
potentially over dozens or hundreds of segments.  Unless you can be sure all
off-the-shelf TCPs will provide an accurate pointer, no pointer can be
relied upon.  This is a good reason for making this feature optional.  Also
you may wish to fully document this behavior to flush out all of these
operational issues.

Doug

> The urgent pointer is to help the iSCSI implementation to
> identify the iSCSI
> message.  Once we know the boundary for command A, it does not take rocket
> science to determine where command B starts.
>
> Y.P.