RE: FCIP/iFCP : Guarantee In-Order delivery for FC N/NL_ports

[Black_David@emc.com]

> > Beyond this, FCIP may have framing issues (identification and placement
> > of inbound data in the presence of drops) that are similar to iSCSI
depending
> > on how the FCIP nodes are implemented.
> > 
> The issue wrt. to framing in an FCIP device is a bit puzzling to me.
Framing
> for an iSCSI HBA for implementing zero-copy DMA semantics I can
understand.
> The notification of delivery and the delivery of data is de-coupled, so
order is
> preserved in this case.

> But, aggressively forwarding through drops in an FCIP bridge is not only
> dangerous, it violates TCP layering. Forwarding around dropped PDU's
> will introduce all sorts of ordering issues. It seems like an FCIP device 
> would want to take the conservative approach and allow TCP to recover
> and deliver the PDU's in the order that they were sent. Hence, I don't see
> a need to specify a framing method for an FCIP-type device.

Depending on the implementation approach to memory management, an
FCIP device may have issues similar to an iSCSI HBA, and this is still
the case even though an FCIP device MUST NOT perform the sort of
aggressive forwarding described in the above paragraph.  YMMV depending
on the physical configuration and software management of memory in
the specific implementation.

--David
---------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
+1 (508) 435-1000 x75140     FAX: +1 (508) 497-8500
black_david@emc.com       Mobile: +1 (978) 394-7754
---------------------------------------------------