Subject: [Tsvwg] TCP Framing for ULP (TUF)

From: Douglas Otis <[email-masked]>
Date: Tue, 11 Dec 2001 10:08:02 -0800 (PST)

There is a basic problem using this structure for
transforming TCP into a datagram transport.  As the
ULP attempts to build segments, there are many
opportunities for this segment to be restructured. 
There is a 48 bit key and a 16 bit length to detect
framing.  Should there be an error caused by
re-segmentation, there is no assurance that such will
not cause a false header to be found.  As each segment
arrival is expected to extract and place this
information prior to seeing the prior length value
with the additional placement occurring as a result of
extraction of the ULP (RDMA as example) further
processing this information.  This placement is NOT
done above TCP but rather below.

Once an error is discovered, there is no means to
recover as the damage will have been done unless you
require a copy of old data to be made so there is no
means to recover.

This below the transport function (RDMA) causes this
shim to sit both above and below the transport (TCP). 
TCP becomes this stuff in the middle of the packet
placement protocol then created.  At that point, TCP
becomes meaningless with respect to how this packet
placement protocol (TUF) works.

This packet filtering together with data placement
happening from data information in the headers
implanted in the hopefully aligned TCP segments means
that applications are now executing below the
transport.  This means that security becomes far more
difficult and any concept of network layers goes out
the window.

If direct placement is desired, use SCTP and add an
offset definition using Payload Protocol Identifier. 
Now you have total assurance that the segment is
aligned, there is a CRC-32c assuring the segment is
correct, and the stream acts as the token for what
vector this offset is to be applied.

This SCTP scheme is simple enough to allow NIC
manufactures to employ this scheme once IANA has
defined the PPI.  This scheme can be used for SCSI,
RDMA, RPC, etc.  It could be used broadly, take
advantage of introduction of SCTP Offload Engines,
(SOEs) where this function would then blow the doors
off of any TCP alternative.

Put away the sharp instruments aimed at fixing TCP, it
looks like you will be doing serious damage.

Doug

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