[T11.3] FCP-4: Continuously Increasing SEQ_CNT

Claudio DeSanti cds at cisco.com
Fri Nov 3 13:38:08 PST 2006

Craig, Bob, Dave,
there are functions defined in FCP-4, such as data overlay or certain 
bi-directional commands, that are simply not implementable in Class 3 
without the use of CISC. I bet that the devices you are referring to do 
not implement these functions. I recommend to identify these functions 
in FCP-4 and either:
a) obsolete them; or
b) clearly state that use of CISC is required to implement them in Class 3.
In addition, the usage of CISC greatly simplifies error recovery in 
Class 3. We should encourage this behavior moving forward. I recommend 
that FCP-4 mandate the support of CISC to FCP-4 compliant devices, but 
not its use. CISC should be mandatory to support and optional to use in 
FCP-4. In this way we set a good path for the future, while allowing 
complete interoperability with FCP-3 and older devices that do not 
support CISC. To ease this interoperability FCP-4 may also recommend to 
not use CISC by default. But mandating its support in FCP-4 devices, we 
achieve that when connecting FCP-4 only devices CISC may be turned on 
and used, with all its advantages.
Craig W. Carlson wrote:
> I’d have to agree with Bob on this one. We are aware of devices which 
> cannot support CISC, and which would seriously break if presented with 
> it. A change such as this (either a or b) could create havoc with 
> device interoperability.
> +Craig
> On 10/13/06 6:08 PM, "Bob.Nixon at Emulex.Com" <Bob.Nixon at Emulex.Com> wrote:
>     Dave,
>     Despite the potential value of CISC to FCP operation in Class 3,
>     we must advise against requiring or even recommending it.
>     In our interoperability testing, we have discovered there are
>     devices with significant installed base that do not behave
>     properly when actually presented with CISC. Unfortunately, they do
>     not reject an N_Port Login that offers CISC, so this problem is
>     not discoverable.
>     Even recommending CISC in a standard would therefore increase the
>     incidence of interoperability problems with use of Fibre Channel.
>     - Bob Nixon, Emulex alternate representative
>     -----Original Message-----
>     *From:* t11_3-bounces at listserve.com
>     [mailto:t11_3-bounces at listserve.com]
>     <mailto:t11_3-bounces at listserve.com%5D>*On Behalf Of *David Peterson
>     *Sent:* Sunday, October 08, 2006 12:34 PM
>     *To:* t10 at t10.org
>     *Cc:* t11_3 at t11.org
>     *Subject:* [T11.3] FCP-4: Continuously Increasing SEQ_CNT
>     Howdy All,
>     At the last FCP-4 working group meeting I presented a proposal to
>     request the use of continuously increasing SEQ_CNT (CISC) for
>     Class 3 service.
>     While most believe requiring continuously increasing SEQ_CNT for
>     Class 3 service is a good idea, one vendor indicated that none of
>     their implementations support CISC, and another vendor was
>     concerned about the requirement.
>     As such, we have the following options:
>     a. require CISC for Class 3 service. This means that existing
>     implementations can claim compliance to a prior standard (e.g.,
>     FCP-3);
>     b. specify that CISC should be used for Class 3 service;
>     c. no change (i.e., CISC is not required except for streamed
>     Sequences).
>     My preference would be option a.
>     What say ye?
>     ...Dave
>     (no disclaimer)
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> ------------------------------------------------------------------
> Craig W. Carlson mailto:craig.carlson at qlogic.com
> QLogic Corporation (952) 932-4064
> 6321 Bury Drive
> Eden Prairie, MN 55346
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