Re: exactly the same protocol ??

[Matt Wakeley <matt@rtl.rose.agilent.com>]

David,

FC-SW and FC-AL are completely different beasts.  FC-SW "specifies tools and
algorithms for interconnection and initialization of Fibre Channel switches to
create a multi-switch Fibre Channel Fabric."  whereas FC-AL defines a protocol
of communication between two or more nodes on a FC loop.

Are you referring to the difference between FC-AL and FC-PH (also known as
N_Port or old port mode)? (I fail to understand why EMC would be connecting
storage boxes up as a fabric switch element.)

If that is the case, this is the definition of how the data is transferred
across the wire, not the definition of the protocol of the data itself.  It's
like comparing ethernet to token ring.  These are two different wire
protocols, but they can (and do) carry the same "data protocol" (TCP/IP, etc).

-Matt Wakeley
Agilent Technologies

Black_David@emc.com wrote:

> With my WG co-chair hat off, it seems that Robert
> Snively and I have different notions of what
> "exactly the same protocol" means.  It would have
> been nice if FC-AL and FC-SW  were exactly the
> same protocol, as it would have saved EMC and a
> number of other companies a considerable amount
> of software/firmware development time and effort.
>
> FC-AL and FC-SW are different protocols at the FC-2
> level that do not interoperate - a device that only
> speaks FC-AL cannot communicate with a device that
> only speaks FC-SW and vice-versa.  FCP (which
> encapsulates SCSI for Fibre Channel) is an FC-4 level
> upper layer protocol that runs over both FC-AL and
> FC-SW.  I don't believe that there are any disk
> drives that speak FC-SW.
>
> --David
>
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> David L. Black, Senior Technologist
> EMC Corporation, 42 South St., Hopkinton, MA  01748
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