On the subject of forward and backward compatibility, I think the
dispatch codes for fragmentation (FRAG1, FRAGN) should be changed to
values that are currently reserved if we move to sending the
datagram_size and datagram_offset as compressed and uncompressed values.
This will mean that during the transition period, it will be much
easier to sort out interoperability problems where some nodes use
compressed values and some nodes are running older code using
uncompressed values.
I don't think the new nodes should support both compressed and
uncompressed offsets / sizes but should simply reject fragments that
don't have the dispatch codes they are expecting.
The existing dispatch codes would not be lost forever as they could be
strongly deprecated and then recycled in a future RFC.
Daniel.
Jonathan Hui wrote:
It would be helpful to know what people's expectations are relative to
what this specific draft should include relative to an acceptable
timeline of getting a document out. Few comments:
- The WG currently does not have a proposal for TCP header compression,
let alone one that we have built some consensus around.
- The RPL protocol mechanisms and headers are still in flux. It is
difficult to propose a concrete way of compressing them without knowing
what they will look like. For example, within ROLL, we will be
proposing ways to "pack" lists of addresses such that common prefixes
are only carried once within the datagram.
- The general 6lowpan-hc format is generic enough to be used on top of
other fragmentation mechanisms and/or frame sizes. Do we really want to
limit its capabilities to a particular fragmentation and frame size?
There always seems to be a tension between splitting functionality
across different drafts vs. delaying the current draft to "sneak" in new
functionality. I'm all for sneaking in fixes to RFC 4944 (i.e. simple
changes to fragmentation) or additional functionality for expediency if
we can realize that expedience. But waiting until we design a TCP
header compression mechanism that we can build consensus around probably
isn't the best approach, in my opinion, and should be left to a separate
draft.
So what do others think?
(I will start a new thread specifically on fragmentation +
forward-compatibility so that we drive towards closure on that specific
issue).
--
Jonathan Hui
On Feb 24, 2010, at 10:55 PM, Robert Cragie wrote:
Hi Geoff,
I concur with Joseph's statements and thus do not support forwarding
the draft to IESG yet.
Robert
Robert Cragie (Pacific Gas & Electric)
Gridmerge Ltd.
89 Greenfield Crescent,
Wakefield, WF4 4WA, UK
+44 (0) 1924 910888
http://www.gridmerge.com
Reddy, Joseph wrote:
Hi Geoff,
I do not support forwarding this doc to IESG yet. I would like the
following issues addressed
** Investigate possible TCP header compression scheme
** Explain strategy for compressing RPL headers ( I understand this
could be done in the ROLL group, but I have not seen a definite
statement either way )
** Resolve the "forward compatability" issue ( ideally, while
maintaining backwards-comptability )
-Regards, Joseph
----------------------------------------------------------------------
Message: 1
Date: Sat, 13 Feb 2010 00:56:31 -0700
From: Geoff Mulligan <[email protected]>
Subject: [6lowpan] WGLC for 6lowpan HC draft
To: 6lowpan <[email protected]>
Message-ID: <1266047791.3643.48.ca...@dellx1>
Content-Type: text/plain
Folks,
I realized that I have made a huge slip-up. The HC draft has
languished for the past few months.
At the meeting in Hiroshima we said that we would last call this
draft, but I failed to send out the actual last call. So...
This note formally starts the WG Last Call for comments on
draft-ietf-6lowpan-hc-06, "Compression Format for IPv6 Datagrams in
6LoWPAN Networks".
The document can be found at:
http://www.ietf.org/id/draft-ietf-6lowpan-hc-06.txt
The document is intended to be submitted by this Working Group to the
IESG for publication as a Standards Track document.
Please review the document carefully (one last time), and send your
comments to the 6lowpan list. Please also indicate in your response
whether or not you think this document is ready to go to the IESG.
Because of my gaffe this Last Call will end Wednesday February 24
2010 at 2359 UTC.
Thanks,
Geoff
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