iSCSI - Change proposal Removing the X bit

["Julian Satran" <Julian_Satran@il.ibm.com>]

Dear colleagues,

We intend to publish very soon version 09 of the draft in its current
format (not many changes) and postpone the editorial changes (already under
way) for 10.

One of the latest change proposal involves removing the X bit.

The X bit has been used in several types of restart/replay but is somewhat
made redundant by the removal
of the command replay.

This involves removing the X bit from request byte 0 and either making it
reserved or "shifting left" the rest of the general-use bits (I and the
direction bit).

It also involves mandating a cleaning NOP.

The cleaning NOP is needed in order to "flush out" old command PDU that can
be left over by simple sequences like the one in the following scenario:

2 connections

On connection 1 I->T c1,c2,c3
On connection 2 I->T c4,c5,c6

Targets receives everything and acts on commands but responses are sluggish
and initiators sees only an ack for
c1.  It then retransmits c2, and c3 while there answer are in flight back
after which the connection is almost dead and not used by initiator.

After a complete wrap around, involving only connection 2,  the target
suddenly gets c2, c3 in a correct window and acts on them.

The need to clean-up old PDUs is common to all protocols that use a
sequence that wraps and we suggested cleaning up using a NOP.  We will
mandate a cleaning NOP only on connections that had at least one "retry".

It looks like we might e able also to abandon the task management -
reassign function and do it with a reissue (with the same NOP cleanout
implication) since retiring the replay function makes the reassign
unambiguous (reissuing a command, after logout, on a new connection -
implies reassign).

Please comment - I need your input urgently.

Julo