iSCSI: new state diagrams for rev09

["Mallikarjun C." <cbm@rose.hp.com>]

All:

Consequent to the feedback I received both online and
offline, iSCSI state diagrams are considerably revamped.
Thanks to all those who provided the feedback.  The new
state diagrams are posted at:

	http://storage-arch.hp.com/iscsi_states_rev09.pdf

The ASCII forms of the above are currently part of rev 08-90
draft that Julian posted on his web.

The major changes are -

- The initiator and target state machines are split for 
  both standard connection diagram and session state 
  diagram.  It is hoped that this separation makes it
  easier to follow.

- Several (informative, but) non-essential states were
  eliminated, since they were waiting for internal events 
  (like acquiring resources) that are likely non-existent 
  in good implementations.  That leaves us with a 7-state
  machine for both initiator and target.

- The reduction of states has a salutary effect on the ASCII
  representation.  I was able to translate all the diagrams
  into ASCII!

- The state descriptions are more descriptive now, specifically
  calling out the event(s) that the state machine is waiting 
  for in that state.

- The transition descriptions are also more descriptive,
  listing the set of events that causes the given transition
  for each of the roles.

- The "connection recovery state diagram" has been renamed 
  as "connection cleanup state diagram" since the word "recovery"
  was inadvertently overloaded.  Connection recovery (the 
  act of reassigning the task allegiance to a different connection)
  happens outside the scope of this state machine depending on
  the operational ErrorRecoveryLevel - all this diagram
  specifies is the dynamics of gracefully closing an active 
  iSCSI connection, perhaps replacing with a new connection.

- Consequent to the above and for general clarity, some 
  states have been renamed to reflect the "wait reason" better.

- Certain missing/incorrect transitions are now fixed -
  like the "close the session" Logout handling etc.

- I added some text on the first slide that describes the
  design philosophy behind the current model, perhaps also 
  can be called design assumptions.


I have only one (likely) open issue on my list.  I received
feedback from one reviewer that the _description_ of the diagrams 
is not "traditional" - for example, the current tabular format 
captures the transitions (each caused by a set of events) in 
a state-state matrix, but does not describe them in terms of 
an event-state matrix for each state (which would run into 
several pages).  The current description scheme seemed quite 
acceptable to myself (and also to Julian among others) - but 
I am open on this.  Please comment if you strongly feel about 
this issue.

Thanks! 
-- 
Mallikarjun 


Mallikarjun Chadalapaka
Networked Storage Architecture
Network Storage Solutions Organization
MS 5668	Hewlett-Packard, Roseville.
cbm@rose.hp.com