RE: iscsi : numerical negotiation wording is ambiguous

["Sanjeev Bhagat (TRIPACE/Zoetermeer)" <sbhagat@tripace.com>]

Julian, Santosh,

Here is what i have to say

In either of the cases reject message is not needed if there is no double
check required.

A reject is needed in both cases to allow some flexibility and i will give
you an example for this

All SCSI devices today available have Sync options for more than 10MB/sec. 

Consider a chip designed which works fine for sync negotiation rate of
upto40MB/sec but misbehaves or behaves illegally for sync options less than
10 MB/sec. In such case a device driver for such a chip will start
negotiating with the SCSI device for 40 MB/sec. If the SCSI device returns a
value of 8MB/sec then in this case the device driver must send a reject
message for sync negotiation. (although it is an illegal condition but it
still allows room for slightly misbehaving devices to operate properly in
Non-SYNC mode). This is my basis of saying that we must have a reject
message in both cases although it is strictly not required. 

Sanjeev
-----Original Message-----
From: Santosh Rao [mailto:santoshr@cup.hp.com]
Sent: Monday, October 01, 2001 8:38 PM
To: ips@ece.cmu.edu
Cc: Sanjeev Bhagat (TRIPACE/Zoetermeer); 'Julian Satran'
Subject: Re: iscsi : numerical negotiation wording is ambiguous


Julian & Sanjeev,

Responding to both your mails......

Julian :

I think you may have mis-interpreted my comments. I believe Sanjeev has
clarified the intent of my suggestions. 

I am *not* suggesting that the responder send back its values and these
be blindly imposed on the originator. On the contrary, my suggestion is
that the computation of the result of the negotiation (higher or lower
of the 2 values) be only performed by the responder and sent back to the
originator.

The result of the negotiation is the same in both cases and there is no
REJECT required in my case nor yours. The difference is the advantages
I've stated in my model. 


Sanjeev, in response to your comment :

" [Sanjeev Bhagat (TRIPACE/Zoetermeer)] Although there is
>  no reject , but it can be a problem in future .
>  Consider your example of DataPDULength in your own
>  message. Suppose offering party sends a value of 16,384
>  (this is also lowest value it can send) and responding
>  party responds with 8,192. In this case the offering
>  party will have to reject the negotiation. So a reject
>  message is needed in this case also. "


There is NO need for any REJECT in the above case. If the initiator
is'nt satisfied with the value returned by the originator and cannot
function with the negotiated values, it can simply close the TCP
connection. There is no need to send any REJECT.


Thanks,
Santosh


> "Sanjeev Bhagat (TRIPACE/Zoetermeer)" wrote:
> 
> Thanks Julian, please find my further comments in the message
> 
>      -----Original Message-----
>      From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
>      Sent: Sunday, September 30, 2001 6:07 PM
>      To: ips@ece.cmu.edu
>      Subject: RE: iscsi : numerical negotiation wording is
>      ambiguous
> 
>      Sanjeev,
> 
>      I am not sure clear I made the tiny diference between what I
>      say and what Santosh said:
> 
>      Santosh says:
> 
>        1. a requester sends A=valuex
>        2. a responder sends B=valuey
>        3. the responder assumes that the value y is the correct
>           value and so does an external observer
>           [Sanjeev Bhagat (TRIPACE/Zoetermeer)] I would rather
>           say it this way the responder computes the value with
>           its own supported values and responds with a value y
>           which the responder thinks is correct and so does an
>           external observer
>        4. the requester checks that valuey is conformant (he will
>           not believe it) and will reject it if not conformant
>           else it will accept it
>           [Sanjeev Bhagat (TRIPACE/Zoetermeer)] Although correct,
>           but it is highly unlikely for the responder to reject
>           the final result because the rule states that (lower or
>           higher of two will be the result) and so the offering
>           party should be able to accept the lower or higher
>           range as defined by rule. In case the key is dependent
>           upon some range of fixed values then the negotiation
>           should be performed as list negotiation and not
>           numerical negotiation.
> 
>           This might be what you "conventionally" do - I don't
>           and that shows that convention like morals are a matter
>           of geography :-)
>           [Sanjeev Bhagat (TRIPACE/Zoetermeer)] :-)
> 
>           The advantage of this set of rules is that it allows an
>           external observer to know what was selected without
>           knowing the rules
>           [Sanjeev Bhagat (TRIPACE/Zoetermeer)] Even in this
>           case, I guess that the external observer has to know
>           the rules to double check the value is correct or not
>           The disadvantage is that messages have to be "built",
>           an additional reject states exists and MOST IMPORTANT
>           you need both messages
> 
>           In what I said:
> 
>           1. The requester sends A=valuex
>           2. The Responder has to send either nothing (if valuex
>           is enough on both sides to compute the result like in
>           the case in which the function is a Boolean AND and the
>           value is NO) or valuey
>           3. Both the requestor and responder have to compute the
>           value (they have to know the rules anyhow) and so does
>           the external observer
> 
>           The disadvantage is that the external observer has to
>           know the rules
>           The advantage is that there is no reject, in binary
>           negotiations you can go away with shorter negotiations
>           and you can set strings at fixed values.
>           [Sanjeev Bhagat (TRIPACE/Zoetermeer)] Although there is
>           no reject , but it can be a problem in future .
>           Consider your example of DataPDULength in your own
>           message. Suppose offering party sends a value of 16,384
>           (this is also lowest value it can send) and responding
>           party responds with 8,192. In this case the offering
>           party will have to reject the negotiation. So a reject
>           message is needed in this case also.
> 
> 
>      Sanjeev
>       "Sanjeev Bhagat
>       (TRIPACE/Zoetermeer)"                    To:        "'Santosh Rao'"
>       <sbhagat@tripace.com>            <santoshr@cup.hp.com>, Julian
>       Sent by: owner-ips@ece.cmu.edu   Satran/Haifa/IBM@IBMIL
>                                                cc:        ips@ece.cmu.edu
>       30-09-01 16:32                           Subject:        RE: iscsi :
>       Please respond to "Sanjeev       numerical negotiation wording is
>       Bhagat (TRIPACE/Zoetermeer)"     ambiguous
> 
> 
> 
>      All,
> 
>      I agree with Santosh that the responding party must respond
>      the result of
>      the negotiation as compared with the value from offering
>      party. All
>      negotiations in SCSI like (sync, disconnect etc) are also
>      done the same way.
>      I also object to Julian's reason of a simple minded target
>      which wants to
>      send certain fixed values only. In case a simple minded
>      target identifies a
>      value which it cannot support or is less than the value a
>      target can
>      support, then there should be a method for target to reject
>      such a
>      negotiation and the default values be accepted on both side
>      as a result of
>      negotiation.
> 
>      1 Because even if simple minded target sends its fixed value
>      which is
>      greater than the value sent by offering party then the final
>      result of
>      negotiation will be taken as ( lesser of the two) and in
>      this case target
>      which which cannot support the lower value will produce some
>      illegal
>      results.
> 
>      2. if simple minded target wants to send its own value and
>      wants it to be
>      accpeted then the responding party is not negotiating but
>      forcing the result
>      on initiator(this method should not be allowed unless
>      explicitly mentioned).
> 
>      however if there is another proposal of numeric negotiation
>      in which the
>      responding party can force its result to be over ridden by
>      the offering
>      party's result then it is acceptable for offering party and
>      responding party
>      to send there own supported key-value result and it can then
>      be computed at
>      offering party's end.
> 
>      IMP: (May be I am missing something here) I do not see how a
>      numeric
>      negotiation can be rejected. Is it possible to reject such
>      kind of
>      negotiaion?
> 
>      Sanjeev
> 
>      -----Original Message-----
>      From: Santosh Rao [mailto:santoshr@cup.hp.com]
>      Sent: Friday, September 28, 2001 11:15 PM
>      To: Julian Satran
>      Cc: ips@ece.cmu.edu
>      Subject: Re: iscsi : numerical negotiation wording is
>      ambiguous
> 
>      Julian & All,
> 
>      I request the group to take a close look at this negotiation
>      process
>      again and [re-]evaluate the alternative being proposed.
> 
>      Further, it appears that the login stage negotiation  is
>      also following
>      the same algorithm as the login key negotiation, wherein
>      originator &
>      responder offer their respective values and both sides need
>      to determine
>      the result of the negotiation. i.e. both initiator and
>      target need to
>      compare their NSG with the other party's NSG and pick the
>      lower of the
>      2.
> 
>      I suggest that both the login key negotiation and the login
>      stage
>      negotiation follow the policy that the originator offers a
>      value and the
>      responder picks the result of the negotiation based on (the
>      offered
>      value & its own value). The value picked by the responder is
>      sent back
>      to the originator.
> 
>      This model has the following advantages :
> 
>      1) Only one side picks the result of the negotiaton. Hence,
>      the 2 sides
>      cannot go out of sync on the value picked.
> 
>      2) The originator knows the negotiated result at the the
>      responder since
>      the responder sends back the result of the negotiation.
> 
>      3) This model is easier to debug because of (1) & (2).
> 
>      4) Less code since only 1 party (responder) needs to perform
>      the
>      computation to pick the result of the negotiation.
> 
>      5) This scheme leaves less room for interop problems and
>      mis-interpretation since it is the more familiar negotiation
>      technique
>      that is in use in most other mass storage protocols. (ex :
>      FC PLOGI, FC
>      PRLI, etc). From a first reading of the current negotiation
>      scheme, it
>      is'nt readily apparent that the currently defined model is
>      different
>      from the above and requires both sides to be picking the
>      result of the
>      negotiation, instead of just the responder.
> 
>      Comments ?
> 
>      Thanks,
>      Santosh
> 


-- 
##################################
Santosh Rao
Software Design Engineer,
HP-UX iSCSI Driver Team,
Hewlett Packard, Cupertino.
email : santoshr@cup.hp.com
Phone : 408-447-3751
##################################