Subject: [tsvwg] draft-tuexen-sctp-udp-encaps-03.txt

From: "Phelan, Tom" <[email-masked]>
Date: Tue, 5 Jan 2010 10:25:55 -0500

Hi All,

Resending this -- I haven't seen it show up in the tsvwg stream, maybe
it fell victim to the SpamAssasin 20XX bug.  Sorry if it gets
duplicated.

Tom P.

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Hi Michael,

Your UDP encapsulation method for SCTP seems elegant to me.  As we've
discussed before, our ADs would like us to keep the SCTP and DCCP
encapsulation methods as aligned as possible so I'd like to comment on
the similarities and differences between this and
draft-phelan-dccp-natencap-03.

At the high level, our approaches are the same -- insert a UDP "shim"
header between the IP header and the "real" transport header.  The ports
in the UDP header indicate the communicating encap/decap services.  The
ports in the real transport header indicate the real transport
connection/service.

My draft doesn't include a diagram similar to yours with the encap/decap
points, but I feel that my approach is compatible with that diagram.
I'll review whether or not including that diagram in my draft would be
useful.

The differences in the drafts seem to me to all be due to the
differences in the protocols being encapsulated.  SCTP was wise enough
to not include an IP pseudo-header in its checksum, it doesn't support
partial checksums, and its native checksum is stronger than the UDP
checksum.  This allows you to directly encapsulate the SCTP payload
without change.  There is a little bit of inefficiency in first
verifying the UDP checksum which covers the entire packet, and then
verifying the SCTP checksum too.  However since the SCTP checksum is
stronger but doesn't cover the UDP header, this seems to be the only
solution possible.

DCCP, on the other hand, does include an IP pseudo-header in its
checksum, supports partial checksums, and uses the same checksum
algorithm as UDP.  Therefore dccp-natencap contains procedures for
dealing with these checksum issues that are not necessary for SCTP.
Also, the changes in the checksum procedures open up a few other
optimizations, and dccp-natencap includes those optimizations.

Tom P.