Hi Jonathan and Zach; That's again my bad wording I guess; We can have up to 16 contexts both directions. Does not mean that all deployments will use 16 context. For a given deployment, there might be 3 of each. In that deployment, all nodes are required to allocate memory for 3. Some nodes might be physically incapable to join a network that requires more contexts than they can allocate.
Is that acceptable? I like Zach's proposal to make the additional context fully optional (for nodes not routers). But then, the source must know that the destination does not support it, and we need to describe that. Then again, I see that the spec needs edition to be clearer but not a change in the formats. What do you think? Pascal >-----Original Message----- >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jonathan Hui >Sent: vendredi 10 octobre 2008 18:11 >To: Zach Shelby >Cc: 6lowpan >Subject: Re: [6lowpan] Fwd: New Version Notification fordraft-ietf-6lowpan-hc-01 > > >Hi Zach, > >On Oct 10, 2008, at 5:58 AM, Zach Shelby wrote: >> 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? > >[jhui] The number of contexts is an issue I raised on the list a few >weeks ago. Many seemed to think that two contexts was okay. However, I >wanted us to be sure that 2 was enough and as a result there was no >change in the number of contexts from hc-00 to hc-01. With an extra >bit (13 bits total) we can certainly support 2 contexts without a >context identifier extension. With two extra bits (14 bits) we can >support 3 contexts. Any more would require an extra byte, I think. Of >course, we can stick with the current encoding but we can limit use to >X < 16 contexts. What do people think? > >> 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'? > >[jhui] Those that are arguing for more than 2 contexts see it useful >for renumbering. If that is the case, then SAA must have the >flexibility for use with contexts other than the default. For now, I >think it's best to consider having a context identifier included with >the 6LoWPAN Prefix Information Option. > >-- >Jonathan Hui > >> >> >> - 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. >>>> >>>> >>> _______________________________________________ >>> 6lowpan mailing list >>> [email protected] >>> https://www.ietf.org/mailman/listinfo/6lowpan >> >> -- >> >> Zach Shelby >> Head of Research >> Sensinode Ltd. >> Kidekuja 2 >> 88610 Vuokatti >> FINLAND >> >> mobile: +358 40 7796297 >> >> This e-mail and all attached material are confidential and may >> contain legally privileged information. If you are not the intended >> recipient, please contact the sender and delete the e-mail from your >> system without producing, distributing or retaining copies thereof. > >_______________________________________________ >6lowpan mailing list >[email protected] >https://www.ietf.org/mailman/listinfo/6lowpan _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan
