We actually discussed this a while back with Erik Nordmark in some detail. The
issue is that an IPv6 link
can have several prefixes, and they are not guaranteed to be advertised in any
particular order by the router
or routers on that link. So one could not use a bit pattern easily to refer to:
* "the" global prefix (cuz there may be more than one)
* "the first global prefix" (cuz node A's first might be node B's second)
At the end we did not see a clear and easy way of doing so, so we limited the
header compression scheme
to only the link-local addresses (cuz the "prefix" in that case in
unequivocally known). It also did not seem
like overall, complicating the basic scheme with additional header compression
for global prefixes was
very meaningful as most traffic would probably be link-local anyways.
In case it is not clear, an assumption above (as in all the format document)
was that we wanted to have
support for IPv6, not for some watered-down or somewhat tweaked (even if only
slightly) version of IPv6.
It was also pretty clear that without this we wouldn't have been able to have a
working group.
That was several years ago, so our assumptions may need to change, and it would
be good to hear
that based on folks' experience, of course.
-gabriel
----- Original Message ----
From: David Culler <[EMAIL PROTECTED]>
To: [email protected]
Sent: Monday, July 16, 2007 4:38:26 PM
Subject: [6lowpan] Looking for feedback on HC1g - stateless header compression
for routable prefix
Folks,
We'd like to draw your attention to I-D
http://www.ietf.org/internet-drafts/draft-hui-6lowpan-hc1g-00.txt
that was posted two weeks ago. It generalizes HC1 to provide the same level of
header compression for a PAN-wide global prefix. HC1 only compresses addresses
that use the link local prefix. A global prefix is always used in
communication with endpoints external to the PAN. It may be used as well
within the PAN. In the context of mesh-under, HC1g applies to originator /
final.
Thanks,
David Culler and Jonathan Hui
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