Subject: [rddp] Comments on draft-stewart-rddp-sctp-00.txt

From: "Hilland, Jeff" <[email-masked]>
Date: Thu, 3 Oct 2002 10:36:44 -0500

First, a general observation:  RDMA does not work without DDP beneath
it.  One of the LLP requirements of RDMA is that DDP be the layer that
does the Direct Data Placement.  RDMA does not place the data, but it
does make cool features like RDMA Read and the STag invalidate
operations work.  Since the charter has declared a separation between
RDMA and DDP exist and RDMA requires DDP, we cannot do just RDMA.  Or,
more correctly, we will not.

So the Adaptation Indication of both RDMA and RDMA+DDP is inappropriate,
since RDMA cannot function without DDP.  There are some who would argue
the list should be DDP and DDP+RDMA.  I personally am not one of them. 

Comments on your questions:

>>1.  Do we need to have a control channel, stream 0 for instance?
To me, this is a ULP (Upper Layer Protocol) issue.  It is not required
by RDMA, by design.  RDMA is expected to run on a single stream.  We
will see examples of ULPs in the near future that may use multiple
streams, but an RDMA features/parameters are negotiated and set by the
ULP and not RDMA.  So neither RDMA nor DDP require control streams.

>>2.  Do we need to dictate control messages that can be sent back to
negotiate different aspects?
Again, this is something ULPs do.  RDMA is architected not to negotiate
anything.  ULPs are expected to pass back and forth STags, number of
outstanding RDMA resources, Flow Control of Untagged Buffers, etc.  So I
don't believe there is any need for this.

>>3.  If we do this do we even need DDP, just have RDMA and then
negotiate things from there?
I think I answered this one in the general observation.  

>>4.  Do we need to better describe how to use unordered data with the
TSN and the CUM-ACK out of the sockets-api?
DDP & RDMA get out of some of the unordered issues by requiring the
Stream be ordered.  And then go into how you might do it if the layers
got muddled.  They try to be transport independent, but it is obvious
that they are TCP oriented - or rather that implementing DDP & RDMA on
TCP have been well thought out.  
So I guess the answer to my question is yes, any informational text that
indicates how to handle ordering issues properly or any other LLP issue
would be welcome (informational?) text.

Regards,
Jeff

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] 
Sent: Thursday, October 03, 2002 6:11 AM
Cc: [email-masked]
Subject: [rddp] I-D ACTION:draft-stewart-rddp-sctp-00.txt

A New Internet-Draft is available from the on-line Internet-Drafts
directories.

	Title		: Stream Control Transmission Protocol (SCTP)
Remote 
                          Direct Memory Access (RDMA) Direct Data
Placement 
                          (DDP) Adaption
	Author(s)	: R. Stewart
	Filename	: draft-stewart-rddp-sctp-00.txt
	Pages		: 11
	Date		: 2002-10-2
	
This document describes a method to adapt Direct Data Placment (DDP) and
Remote Direct Memory Access (RDMA) to Stream Control Transmission
Protocol (SCTP) RFC2960 [2] using a generic description found in
[RDMA-Draft] [4] and [DDP-Draft] [3] This adaption provides a method for
two peers to know that each side is performing DDP or RDMA thus enabling
hardware acceleration if available.

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