Hi Julien,
So here's the tension that we have now: From what I saw on the list,
most people were happy with just two contexts. Adding support to the
*base* encoding (i.e. without need of using a context identifier
extension) would require adding yet another bit to the base encoding.
This is in addition to whatever bits we may add depending on whether
you convince us of those additional cases :-)
Regarding 8 bits to encode address compression, I agree with Pascal in
that you should compare against what is in ietf-6lowpan-hc-01 (6
bits). If we find need in supporting your cases, then we should
compare to what I sent out to the mailing list (7 bits). I think the 7-
bit version covers all the cases you were asking for, but maybe I
missed some? Anyways, looking forward to see your 8-bit proposal.
Thanks.
--
Jonathan Hui
On Oct 13, 2008, at 1:24 AM, Julien Abeille (jabeille) wrote:
Hi Zach,
I second your concern
There was recently a discussion specifically about the number of
contexts needed.
There seemed to be a consensus that multiple contexts was useful for
renumbering only, which is rare, and that 2 contexts was enough.
Was there new input since then which justifies the use of 4-bit
contexts?
Cheers,
Julien
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Zach Shelby
Sent: vendredi 10 octobre 2008 14:58
To: Jonathan Hui
Cc: 6lowpan
Subject: Re: [6lowpan] Fwd: New Version Notification
fordraft-ietf-6lowpan-hc-01
Hi,
Here are my comments on hc-01. Overall I think we are quite close with
the comments from Pascal and Julien.
I found the DDF name confusing. Now it has been renamed CTX in the
latest formats on the list, great.
As Pascal pointed out, nodes need to be able to decode all these
options. One thing that worries me in having 16 contexts, is that
nodes
are forced to store them all. That is worst case 272 bytes of memory
consumption. Worth it? Is it possible that an ultra-simple node would
only have to understand the default context?
The default context identifier '0000' could be clarified more in the
draft. When CTX is '10' then the default context identifier '0000' is
used. It should be made clear that this is the prefix advertised in
RAs
as useable for SAA.
Regarding the ND for 6lowpan draft, HC-01 means we need to add a 4-bit
context identifier flag to the 6LoWPAN Prefix Information Option. To
make things clear that should always be '0000' if the A flag is '1'?
- Zach
Jonathan Hui wrote:
http://tools.ietf.org/html/draft-ietf-6lowpan-hc
This new version reflects the recent discussions on the list. The
changes are:
- HC back to 1 byte by default by stealing a few bits from the
dispatch field.
- Added better support for multicast address compression.
- Fixed alignment for UDP port compression.
- Better support for Traffic Class and Flow Label compression.
- Pascal joined as an author.
Happy reading!
--
Jonathan Hui
Begin forwarded message:
From: IETF I-D Submission Tool <[EMAIL PROTECTED]>
Date: October 8, 2008 7:15:35 PM PDT
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]
Subject: New Version Notification for draft-ietf-6lowpan-hc-01
A new version of I-D, draft-ietf-6lowpan-hc-01.txt has been
successfuly submitted by Jonathan Hui and posted to the IETF
repository.
Filename: draft-ietf-6lowpan-hc
Revision: 01
Title: Compression Format for IPv6 Datagrams in 6LoWPAN
Networks
Creation_date: 2008-10-09
WG ID: 6lowpan
Number_of_pages: 15
Abstract:
This document specifies an IPv6 header compression format for IPv6
packet delivery in 6LoWPAN networks. The compression format relies
on shared context to allow compression of arbitrary prefixes. This
document specifies compression of multicast addresses and a
framework
for compressing next headers. This framework specifies UDP
compression and is prepared for additional transports.
The IETF Secretariat.
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--
Zach Shelby
Head of Research
Sensinode Ltd.
Kidekuja 2
88610 Vuokatti
FINLAND
mobile: +358 40 7796297
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