Re: Status summary on multiple connections

[Michael Krause <krause@cup.hp.com>]

At 07:28 AM 10/2/00 -0700, Matt Wakeley wrote:
>I think the layering is being blurred.  Remember, whether there is RDMA or
>not, TCP is the layer doing the ACKing, *NOT* iSCSI.  And whether or not there
>is RDMA or not, TCP cannot ACK TCP segments that arrive out of order until the
>missing ones arrive (it can SACK them, but it can't ACK them - and SACK is
>only informative).
>
>iSCSI cannot deliver commands out of order to the SCSI layer.  So even if the
>command is RDMA'd into a buffer, it cannot be delivered to SCSI until the
>previous commands are received.

This last point is still very important.  One can DMA to memory (SEND or 
RDMA semantics) without posting the completion event to the upper layers 
(iSCSI) thus relieving the responder from having to buffer all of this 
within the chip / adapter.   There is a transport level ACK from TCP 
indicating all bytes for a given message have been received and then there 
is a iSCSI response which is a higher-level completion message which is 
generated once TCP has indicated all bytes up to a given value have been 
properly received.

Mike