Subject: [rddp] A consensus call and a poll

From: [email-masked]
Date: Mon, 16 Dec 2002 19:29:45 -0500

In the attempt to accomplish something that looks like
progress the WG chair has the following to say ...

(1) Having seen no defenders of a prohibition on packing
	multiple ULPDUs into a TCP segment, I believe the
	rough consensus of the RDDP WG that packing of
	multiple ULPDUs into a TCP segment MUST be supported.
	Anyone who disagrees should post that fact to the list
	along with a technical rationale.

This applies primarily to receivers.  Senders have some
leeway to decide how much to send, but need to avoid
doing silly things like sending lots of small packets
when one larger one was feasible based on what was in
the transmit queue at the time.  See Sections 1.3.5 and
6.1 of RFC 2960 (SCTP) for more on what this means for
senders, as well as the Bulk Transfer discussion in
Section 4.2.3.11 of RFC 1122.

(2) I want to try to establish some direction on the approach
	to sender alignment (do TCP segments in general start on
	ULPDU boundaries under normal/reasonable conditions?).
	For now, I'm looking to set general direction, with the
	caveat that there may be exceptions (e.g., due to MTU,
	EMSS, or RWIN shrinkage) for which a design may or may
	not break alignment -- i.e., I'm deferring setting
	direction on alignment in exceptional cases now.
	
	Since I believe that many of the list members prefer
	an aligned approach, I want to gauge the level of
	alternate views and make sure I understand the technical
	reasoning behind them.  From what I recall of traffic
	to the list, Somesh Gupta and Shridhar Mukund oppose
	requiring alignment, and Jim Williams would prefer
	not to require alignment, but could accept that as a
	compromise that omitted other more objectionable features.

	So, let me ask those three people, plus anyone else
	who is opposed to a general approach of requiring
	sender alignment to send me a brief email off the list
	summarizing their viewpoint and the reasoning behind it.
	While I'd like to see these emails this week, I recognize
	that the holidays are coming, and hence won't post a
	proposed rough consensus on direction until after January
	1st. 	Please limit the reasoning to technical points - I'd
	prefer to keep IETF process considerations out of this
	to the extent possible, even though I'm well aware that
	TSVWG and TSV AD approval will be necessary for whatever
	we do in this area, and I will exercise my judgment to
	try to avoid setting a direction that would have no
	chance of gaining these two required approvals.

This is somewhat risky - under other circumstances, I'd defer a
decision on a topic with this level of divergent viewpoints to
the next IETF meeting, but I'm concerned that failure to set a
direction here risks stalling work on the TCP mapping.  Even if
an alignment direction results, it is still the case that the
onus is on the WG to provide strong assurance that a changed
(aligned and framed) TCP talking to an unmodified TCP cannot
lead to confusion about whether the bytestream is framed or not
- I'm reminded that our Area Director used the word "prove" in
describing what he expects of the WG in this area at our
meeting in Atlanta, so people should not take this lightly.

Thanks,
--David

----------------------------------------------------
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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