Draft tutorial for IEEE company_id based FC-PH identifiers

Mike Wenzel mw at core.rose.hp.com
Tue Dec 3 11:46:28 PST 1996

* From the SCSI Reflector (scsi at symbios.com), posted by:
* Mike Wenzel <mw at core.rose.hp.com>
Hi Ralph,

I've been closely following the issues surrounding unique identifiers.  Since
Bob hasn't responded yet, here is my take on your question:

At 09:28 PM 12/1/96 -0600, ROWEBER at acm.org wrote:
>If IEEE expects companies to use a single company_id until the number space
>based on that company_id is "substantially exhausted", then will IEEE expect
>SCSI implementations to use substantially all values associated with an
>IEEE Registered Extended format?  Or, will IEEE be generous and allow
>a company to obtain a new company_id when the number space associated
>with the IEEE Registered Name format is substantially exhausted?
>Stated differently, will IEEE (by virtue of their "substantially exhausted"
>requirement) force FC implementations to use the 128-bit format instead of
>the 64-bit format?

The requirement is to demonstrably conserve (at least not waste) the values
in the first 64 bits of these formats--what Bob refers to as the "Vendor
Specific Identifier".  In effect, the requirement is to conserve this 64-bit
value the same way companies have been conserving the 48-bit Ethernet address
values for years.  There is no requirement to use up the values in
the second 64 bits of an identifier (i.e., the Vendor Specific Identifier
Extension).  Also, a vendor can use any means he wants to to create and 
sub-administer fields within the Vendor Specific Identifier (subfields 
known only within the company).  It is in everyone's best interest for a 
vendor to use the 128-bit format for IDs applied to objects that will
proliferate, like floppy disks, tape cartridges, or virtual chunks of 
storage in a large disk array (possibly 1000's of LUNs per box).

It isn't so much IEEE that is really behind this requirement as it is all
of us who strongly feel there is a need for relatively compact, yet unique
identifiers.  NO ONE wants to see the 24-bit company_id space become
exhausted!  As much as possible, each company needs to do as much as it
can with just one company_id value before it gets another.  Otherwise, 
if company self-discipline doesn't work, then the whole basis for compact
uniqueness will be undermined and we'll all have to come up with other
mechanisms, certainly involving MUCH larger byte strings.  It's a somewhat
delicate, engineering balance between uniqueness and tractability.  So far,
this is working pretty well.  In the 15 years(?) or so that Ethernet has been 
around, only about 1000 company_ids have been assigned.  So there is 
sufficient headroom left for these new applications.  I think we all want to
preserve this happy state.

Best Regards,


 ************* |  Mike Wenzel,
 *****   ***** |  Hewlett-Packard - NCD System Interconnect Lab,
 *** /_  _ *** |  Mailstop 5601,
 ** / / /_/ ** |  8000 Foothills Blvd.,
 ***   /   *** |  Roseville, CA 95747-5601
 *****   ***** |  E-mail: mw at core.rose.hp.com
 ************* |  Telephone (916) 785-5609  FAX (916) 785-2875
* For SCSI Reflector information, send a message with
* 'info scsi' (no quotes) in the message body to majordomo at symbios.com

More information about the T10 mailing list