Subject: [Tsvwg] Intel Forum presentation of RDMA

From: "Douglas Otis" <[email-masked]>
Date: Thu, 28 Mar 2002 12:11:35 -0800

FWIW: Intel Developer Forum Conference, Spring 2002 Feb, 27th.

James (Jim) Pickerton presenting for Microsoft endorsed TUF-TCP/RDMA as the
solution for the future and stated TUF was winning approval within the IETF.
When I asked why TUF rather than SCTP, Jim responded that SCTP was too new
and buggy and would not be ready for at least five years.  He also added
that TUF could be implemented by changing as few as 105 lines of code within
the TCP stack.  The 'call to action' was all applications should incorporate
TUF within their next generation.

TUF is not enough.  This draft does not elucidate what lines of code are to
be changed within TCP.  The transport must be seen as the means of accessing
the IP layer.  How this layer is accessed should be included in a document
adding additional mechanisms for either the IP or TCP layer.  From this
draft it is not clear what layer is even being modified.

The presentation referenced Bernard Aboda's web site for further
information:
http://www.drizzle.com/~aboba/RDMA/rdma-faq.html

Once again a touted RDMA FAQ mis-information that should be corrected.

"2.3 What about SCTP? Can’t SCTP be used to solve the problem?
SCTP addresses the head-of-line blocking issue. SCTP chunking does not solve
the header alignment problem because only the first chunk will be
self-describing. SCTP also does not provide RDMA semantics, for example
random access memory operations.

SCTP streams (or TCP connections) can not be used to effect header data
splitting because ULPs generally require in-order delivery between headers
and data."

The SCTP TLV structure is the type of structure used in IPv6 as an effective
way of bundling objects.  Within SCTP these objects are aligned to 32 bit
boundaries as well.  The benefit is consistent packet size.  I would also
hope that the SCTP-DDP shim draft makes the issue of header/payload
splitting clear.  Each packet within this scheme is independent of the next
and does not require ordered delivery to incorporate DDP headers.  The
number of exceptional conditions created by the TUF scheme together with a
tacit recommendation of improved error checking makes hardware
implementations of TUF-TCP problematic and application specific.  RDMA was
presented as an ultimate general transport of which other protocols must
adopt.  When asked from the audience about the relative lack of security
offered by TCP/RDMA, "It is no worse than TCP and one could always use
IPSEC."

Doug

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