Subject: RE: [rddp] RDDP Atlanta agenda

From: [email-masked]
Date: Sun, 27 Oct 2002 09:59:16 -0500

> I'm confused whether Framing protocols are discussed by RDDP 
> or TSVWG? Pls advise.

The answer is "both" because it depends on what is meant by
"Framing".  MPA and IFT should both be on the TSVWG agenda and TSVWG
should meet before RDDP.  IFT will also be on the RDDP agenda
as it appears to be a good start on the following RDDP work item:

  4) A mapping of the direct data placement protocol onto TCP, for
  informational, because TCP's service is a less good match to RDDP,
  including an applicability statement of the issues regarding the
  service available from the mapping. 

MPA cannot be taken up in RDDP because it makes changes to TCP,
specifically TCP sender behavior.

Thanks,
--David
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David L. Black, Senior Technologist
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953 **NEW**     FAX: +1 (508) 293-7786
[email-masked]        Mobile: +1 (978) 394-7754
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---

From: Caitlin Bestler <[email-masked]>
Date: Sun, 27 Oct 2002 10:10:56 -0600

On 10/27/02, [email-masked] wrote:

>> I'm confused whether Framing protocols are discussed by
>> RDDP or TSVWG? Pls advise.
>
>The answer is "both" because it depends on what is meant
>by "Framing".  MPA and IFT should both be on the TSVWG
>agenda and TSVWG should meet before RDDP.  IFT will also
>be on the RDDP agenda as it appears to be a good start on
>the following RDDP work item:
>
> 4) A mapping of the direct data placement protocol onto
> TCP, for informational, because TCP's service is a less
> good match to RDDP, including an applicability statement
> of the issues regarding the service available from the
> mapping. 
>
>MPA cannot be taken up in RDDP because it makes changes to
>TCP, specifically TCP sender behavior.
>

How does MPA (or IFT for that matter) change TCP? Nothing
that either sends cannot be accomplished with existing TCP
stacks. (I wouldn't implement that way, but you *could*).

I think a more valid distinction between the roles of RDDP
and TSVWG is that RDDP is only interested in solving this
problem for one protocol, whil e TSVWG is presumably looking
for a general solution.

The RDDP-specific solution might have problem-specific
features, such as enabling out-of-order processing and
providing greater error checking than TCP alone does.

In that sense MPA has either one or two features that are
probably not of wider TSVWG interest (out-of-order and CRC32
protection). IFT has split CRC32 protection. While not
explicitly for DDP, it has hard to imagine a use for
splitting header/payload CRC protection in a wire protocol
other than enablilng cut-through direct placement of the
payload.

Despite the fact that both of these proposals solve problems
that might not be viewed as universal to all protocols, they
are both still very simple. It might make sense to deploy
them for more applications that just DDP.

Caitlin Bestler
http://asomi.com/CaitlinBestler/
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