Hi Jonathan, all,
Sorry for the long email, tell me if not clear:
*******************************************************
I agree with the status and the three possibilities:
- 6 bits, most important cases compressed
- 7 bits, all cases I mentionned compressed
- 8 bits, all cases I mentionned compressed, simpler?
Time I propose something for 8-bits as you say :-) :
*****************************************************
8 bit proposal:
*****************************************************
- about contexts: 3 contexts stored, LL context (00), global prefix
context 1 (01), global prefix context 2 (10, used for renumbering)
- encoding:
| SAC | SAM | DAC | DAM |, 2 bits each, as in initial draft.
- meaning
SAC:
00 context 00
01 context 01
10 context 10
11 no context
SAM:
If SAC = 00, 01, 10 prefix fetched from context number "SAC"
00 64 bits compressed
01 16 bits compressed
10 0 bits compressed
If SAC = 11
00: unspecified
01: 128 bits inline
DAC:
00 context 00
01 context 01
10 context 10
11 no context
DAM:
If DAC = 00, 01, 10 prefix fetched from context number "DAC"
00 unicast 64 bits compressed
01 unicast 16 bits compressed
10 unicast 0 bits compressed
11 multicast unicast prefix based FFxx::xxxx:plen:prefix:xxxx:xxxx
If DAC = 11
00: 128 bits
01: FF02::xx
10: FF0x::00xx:xxxx
11: FF0x::00xx:xxxx:xxxx
******************************************
Comparison of 7 -bit and 8- bit is attached as csv, should open ok in
Excel
******************************************
instead of pseudo code, I do the following:
- list all cases supported for src and dest formats (A to E for src, 1
to 9 for dest)
- tell which combination of both are possible (e.g. A1, A2 ... Because
not all combinations are accepted by IP)
- for each combination, tell values of CTX and M bit for 7-bit, SAC,
SAM, DAC DAM for 8-bit. I group the 64/16/0 IID cases to be more
concise.
i.e. for src link local unicast and dest link local unicast CTX 00,
M 0
- based on this, for each src and dest case splitted again, I give
values of CTX, M
i.e. if dest is FF0X::00XX:XXXX, CTX is ...
What you can see:
- with 8 bit, each individual case (A, B,... For src and 1,2... For
dest
) corresponds to a unique value of SAC, SAM...
- with 7 bits, some src cases corresponds to multiple values because
they depend on the dest case, and vice versa
For me, merging src and dest context add a lot of complexity.
******************************************
Comparison of 6-bit and 8- bit
******************************************
I does not make a lot of sense on the complexity side, as they do not
provide the same features.
However, the binding between src and dest context in the 6 bit case
creates the same problem as with 7 bit
Cheers,
Julien
-----Original Message-----
From: Jonathan Hui [mailto:[EMAIL PROTECTED]
Sent: lundi 13 octobre 2008 17:36
To: Julien Abeille (jabeille)
Cc: Zach Shelby; 6lowpan
Subject: Re: [6lowpan] Fwd: New Version Notification
fordraft-ietf-6lowpan-hc-01
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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<hc.csv>
