Hi,
I don't think the consensus changed from that 2 contexts is enough.. it
was just mentioned that with more someone may figure out what to do with
them (renumbering). If renumbering is the only case for having a 4-bit
context identifier, then I recommend Jonathan tries to integrate a short
1-2 bit context identifier into the base format as he mentioned is
possible, thus avoiding the 1 byte extension for 4-bit identifiers. 2-4
contexts will be plenty, and thus we wouldn't be using memory on all
nodes, or having to deal with some nodes supporting 16 and some
supporting 2. Considering that we have only a link-local context in
RFC4944, having 2-4 global contexts is already a huge improvement!
So I would give like to see 1-2 context ID bits for source/dest in the
base header, as a priority over supporting a large range of multicast
address types.
- Zach
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.
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FINLAND
mobile: +358 40 7796297
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