Target-initiated ABTS in FCP

Kurt Chan kc at
Mon Jun 20 09:58:39 PDT 1994

| I do not think this requirement should be eliminated.
| There are many reasons FCP requires ambiguous exchanges to be aborted,
| but one of them is in the following case:
| 1. The initiator has given sequence initiative to the target and the
| target has been sending data frames to the initiator and some of the
| frames are unacknowledged.
| 2. The Initiator sends a Clear Task Set.
| 3. If the target does not abort the exchange, then the initiator may
| assume that it can reuse the exchange and sequence ID in a new
| exchange.
| 4. Later, the frames from the ambiguous sequence may reappear and
| cause a data integrity problem.
| For this case and other reasons, I do not believe that FCP should be
| changed. Targets must continue to be required to terminate exchanges
| in ambiguous states.
|                                  Giles Frazier
|                                  IBM Austin

There are two valid topologies where (4) above will never happen:

- closed loops
- fabrics which are enforcing sequential delivery in conjunction
  with Targets which will not retry frames on BSY.

The FCP requirement is therefore unnecessary for a broad range of
cost-reduced systems.


   Kurt Chan               Hewlett-Packard        System Interconnect Lab 
   kc at     Voice: 916-785-5621    Fax: 916-785-2875       
   8000 Foothills Blvd     MS R5NF                Roseville, CA 95747     

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