Should SIP require detection of duplicate tags?

Steve Finch TFINCHS%A1.VAX2T.mrouter at vax2t.tus.ssi1.com
Wed Apr 13 08:56:58 PDT 1994


Currently, SAM states that the requirement to detect duplicate tags is 
determined by the appropriate protocol standard.  The reason is that for 
some protocols the set of possible tags is enormous.

How bit is enormous?  SIP can have 15 initiators and up to 256 tags per 
initiator, for a total of 65,280 possible tags.  Is this enormous enough?

There are only two conditions that duplicate tags will ever be issued:  a 
broken host computer, or a qualification program designed explicitly to 
test duplicate tag detection by a target.

The real question is:  should a target device be REQUIRED to protect the 
system from an errant host who is issuing duplicate tags?  Yes, this 
capability would help detect strange errors like the host picking or 
dropping bits in hardware as it assigned tag numbers.  But if this is a 
concern, maybe we should add a command verification phase to SIP to make 
sure that the write he just issued was really to block 1354 and not 1350 
with a bit error. 

Why burden a target with the requirement to add a capability that is only 
needed if the system is broken?  No sane host ever issues duplicate tags, 
and insane hosts can do a lot worse things than sending duplicate tags.

Since SAM does not require duplicate tag detection, let's not require it in 
SIP.

Comments?





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