RE: iSCSI: Flow Control

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

Pierre,

Perhaps we should break-out flow control from encapsulation.  Within a draft
to illustrate use of SCTP, is included a flow control as part of the
encapsulation prefix.  As each stream essentially is sitting upon a
connection to SCSI medium, flow control must ensure the depth of this
connecting FIFO.  Thus the appropriate control would be Buffer-to-Buffer
(Class 3).  As time is critical, even 8 MB can represent 1 second of delay.
It should be up to the initiator to decide what has priority within each
stream, but this proposal also allows a higher priority stream connection so
that the application could bypass buffers should there be a significant
queue at the initiator or portal.  As the network connection may represent
less than a normal rate, such priority may prove helpful in cases such as
index retrieval or other information that must come ahead of other
information within the application process.  As buffer depth is the
parameter controlled, it makes little sense to control data and commands
separately.  Dropping data as a method of control remains possible using
just FCP encapsulation and perhaps is a valid selective discard, but this
should be used as a last resort but no discards are required within normal
events.

see:
http://search.ietf.org/internet-drafts/draft-otis-fc-sctp-ip-01.txt

Doug