Subject: Re: [Tsvwg] FW: I-D ACTION:draft-culley-iwarp-mpa-00.txt

From: Joe Touch <[email-masked]>
Date: Fri, 27 Sep 2002 12:47:22 -0700

Teisberg, Robert wrote:
> 
>>-----Original Message-----
>>From: Joe Touch [mailto:[email-masked]]
>>
>>Agreed. However, if the data is placed to the application and the 
>>connection closed before TCP receives the data in the gap, it CANNOT 
>>EVER be acked. That's why it -breaks- TCP.
> 
> Only if placing data in the buffer and delivering it to the application
> are considered synonymous.  If TCP places data, subsequently finds itself
> unable to ack it, and consequently chooses not to notify the application
> (i.e., deliver it), TCP isn't broken.

Agreed. But placing it in a buffer shared by an application requires 
in-order placement. Otherwise, there need to be locks that prevent the 
application from getting at data _until_ the TCP has ACK'd it.

> Now I agree that it's extremely tricky at best (maybe impossible) to
> specify the behavior of MPA in isolation in a way that clearly disallows
> broken implementations' passing themselves off as TCP.  This exchange
> between you and Paul last week:
> 
>>>This would need to be a requirement of the MPA draft, or the multiple 
>>>component drafts would need to require concurrent use.
>>><prc> I happen to agree with you, but some of the other authors believe
>>>that it is inappropriate to -ever- place a hard requirement on a ULP.
> 
> looks like a start at addressing that problem.

It depends on the ULP. If the ULP is considered part of MPA-TCP, then 
the suite together still has to enforce the in-order visibility, or 
provide locking, as per above.

Can this be done with a particular ULP? Sure. At that point, MPA-TCP+ULP 
starts to recapitulate the structure of zero-copy TCP stacks. A 
standardization of that might indeed be useful, but my impression from 
previous emails was that the overarching WG (RDDP?) was specifically 
opposed to such bundling.

Joe

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From: "Teisberg, Robert" <[email-masked]>
Date: Fri, 27 Sep 2002 14:25:41 -0500