I would definitly be in favor of fewer contexts and agree with your
reasons.  I liked the scheme in HC-00 where you could always use CP or link
local.  That seems to cover the common case very well.

Steve

On Tue, Sep 23, 2008 at 9:43 AM, Jonathan Hui <[EMAIL PROTECTED]> wrote:

>
> In moving the HC draft from -00 to -01, we added support for multiple
> compression contexts so that more than one prefix (other than link-local)
> can be compressed.
>
> The obvious question now is how many contexts are enough? It is clear that
> two contexts are useful (one for the 6LoWPAN and another for the common
> destination that all nodes may be sending to). But should we add more?
>
> Some thoughts:
> - Fewer contexts allow the HC encoding to use fewer bits in identifying the
> context in use.
> - Specifying support for X contexts requires nodes to allocate enough
> memory to maintain X contexts (ip addresses, timers, etc.).
> - Additionally, we cannot simply say that we will change X to some larger Y
> at some future date since the nodes that only support X will not be able to
> support Y > X contexts.
> - One argument for supporting more contexts is that it allows network
> renumbering while allowing all nodes to communicate with compressed
> addresses. My thought, however, is that renumbering of 6LoWPAN networks
> should be rare and when they do occur it is okay to incur some extra cost
> and communicate with full addresses during that time.
>
> So my thought is to keep the number of supported contexts small (2). What
> do other people think?
>
> --
> Jonathan Hui
>
>
>
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