Subject: [rddp] RE: changes to TCP?

From: [email-masked]
Date: Mon, 28 Oct 2002 06:21:37 -0500

Caitlin,

> 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*).

IFT does not change TCP, and is quite explicit about that.

Between never packing ULP PDUs into TCP segments and requiring
that TCP segments start/end on ULP PDU boundaries, MPA changes
TCP sender behavior rather dramatically (same sequence of application
sends results in very different packets on the wire, even after
accounting for MPA's added data [length, markers, pad, CRC]).  Among
the issues here is that the resulting behavior is clearly is at
odds with the spirit (and probably the letter) of this text
from Section 4.2.3.11 of RFC 1122:

                 Experience has shown that a TCP
                 implementor needs to verify the design on two extreme
                 traffic patterns:

[... Single-character Segments text snipped ...]

                 o    Bulk Transfer

                      When TCP is used for bulk transfer, the data
                      stream should be made up (almost) entirely of
                      segments of the size of the effective MSS.
                      Although TCP uses a sequence number space with
                      byte (octet) granularity, in bulk-transfer mode
                      its operation should be as if TCP used a sequence
                      space that counted only segments.

Likewise, forbidding use of the Nagle optimization in all cases (no
matter what the ULP) is also problematic.  Both of these are tsvwg
issues, and all further discussion should be on that list, not rddp.

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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