On Jul 9, 2010, at 10:42 AM, 6lowpan issue tracker wrote: > #88: Space optimization in RS/RA > --------------------------------+------------------------------------------- > Reporter: z...@… | Owner: z...@… > Type: enhancement | Status: new > Priority: minor | Milestone: > Component: nd | Version: > Severity: - | Keywords: > --------------------------------+------------------------------------------- > Several space optimizations have been suggested for the information > carried in RAs, in particular the combination of ABRO, PIO and 6CO is > getting very large (already requires fragmentation). Can we avoid or > minimize fragmentation by optimizing these somewhat? Current suggestions > on the table: > > 1. PIO in classic ND only allows to set option length to 4 and there > are 8 bytes you don’t use. Could we set it to 3 to save 8 bytes? The > problem with this suggestion is that the last 8 bytes are used with the R > bit is set.
Looks like this shouldn't be done, so as not to loose RFC4861 compatibility. > 2. Allowing for a default CID=0 using information in the > PIO and/or ABRO options. Currently the prefix is carried in all 3 options: > ABRO, PIO and 6CO. How to reduce the overlap? I have a proposal here. We can elide the 6CO in cases where there is an RA with an ABRO and a single PIO. This can be done with a new flag in the ABRO (Context Flag) which indicates that the PIO in this message is used to form the CID=0 context information. The elided 6CO fields are implied as: Context Prefix = Prefix from PIO Length = Length from PIO CID = 0 C = true if valid lifetime > 0, false if valid lifetime = 0 Valid Lifetime = Valid Lifetime from PIO This is actually going to be the setup in most 6LoWPAN networks, where a CID is assigned only to a single default prefix. This would typically save 16 bytes. Thoughts? Zach > > 3. Colin suggested ICMPv6/ND optimization using HC next-header > compression. Would it require us to add a work item for that in a future > charter? > > -- > Ticket URL: <http://wiki.tools.ietf.org/wg/6lowpan/trac/ticket/88> > 6lowpan <http://tools.ietf.org/6lowpan/> > -- Zach Shelby, Chief Nerd, Sensinode Ltd. http://zachshelby.org - My blog "On the Internet of Things" http://6lowpan.net - My book "6LoWPAN: The Wireless Embedded Internet" Mobile: +358 40 7796297 _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan
