Re: iSCSI: new draft

[David Robinson <David.Robinson@EBay.Sun.COM>]

Are we again presuming that you can do anything to a TCP stream
out of order? If you miss a segment there is not much you
can do with the segments that may follow out of order. Although
you can buffer them, you might as well throw them away as they
WILL be resent. So even if you know the next message boundary
it gives you NO useful information until the entire
contents of the message arrives.  The easy way to minimize
tempory storage is to just drop it if you are memory
constrained.

	-David

julian_satran@il.ibm.com wrote:
> 
> JP,
> 
> No. If a packet arrives very late and others precede it, or a packet is
> lost and recovered with SACK later
> you end up having to pile-up a lot of data in an adaptor or a separate
> memory area until you can figure where to put it. The amount can be
> minimized if you can rapidly figure out where the next boundary is.
> Obviously you do not really hand the data to the user until you have it all
> but you gain by having a place to store it sooner and minimize the amount
> you have to keep in "temporary storage".
> 
> Julo
> 
> Raghavendra Rao <jpr@divyaroot.India.Sun.COM> on 08/11/2000 03:23:50
> 
> Please respond to Raghavendra Rao <jpr@divyaroot.India.Sun.COM>
> 
> To:   Julian Satran/Haifa/IBM@IBMIL
> cc:
> Subject:  iSCSI: new draft
> 
> Julian
> 
> I've trouble in interpreting this in the new draft
> 
> >   Unfortunately, when relying solely on the "message length in the
> >  iSCSI message" scheme to delineate iSCSI messages, a missing TCP
> >  segment that contains an iSCSI message header (with the message
> >  length) makes it impossible to find message boundaries in subsequent
> >  TCP segments. The missing TCP segment must be received before any
> >   following segments can be processed.
> 
> This suggests that TCP might deliver a stream with a missing segment !
> TCP will not deliver to session layer until the missing segment arrives
> to satisfy the streaming protocol it defines.
> 
> Have I misread something ?
> 
> Thanks
> 
> -JP