For many of the same reasons, early versions of the improved hc draft
(before it became a WG doc) did not make use of the PAN ID to create
an Interface ID and left it to all zeros. If you really wanted
something other than all zeros (e.g. the 'symbolic' PAN ID), then use
context information with a longer prefix to indicate what those non-
zero bits are.
Including this within the next rev of 6lowpan-hc is worth discussion.
It certainly is related, but not limited to HC.
--
Jonathan Hui
On Mar 5, 2010, at 7:39 AM, Colin O'Flynn wrote:
Hello,
Hmm, makes sense to me. Would it be possible to get a recommendation
in
hc-06 before WGLC, or where else would it make sense?
As it's difficult to use hc06 with 16-bit addresses unless you
decide on
which way this will work.
Regards,
-Colin
-----Original Message-----
From: Richard Kelsey [mailto:[email protected]]
Sent: March 5, 2010 2:39 PM
To: Colin O'Flynn
Cc: [email protected]
Subject: Re: [6lowpan] 6lowpan 16-bit PAN-ID Field
From: "Colin O'Flynn" <[email protected]>
Date: Thu, 4 Mar 2010 22:59:22 -0000
RFC4944 has the quote:
First, the left-most 32 bits are formed by concatenating 16 zero
bits to
the
16-bit PAN ID (alternatively, if no PAN ID is known, 16 zero bits
may be
used). This produces a 32-bit field as follows:
How does a receiving node know if zero's have been used there to
recreate
the IP addresses? Unless I'm missing something, this seems to be a
ambiguous
case. It seems unlikely a node will know it's short address but not
PAN-ID.
I am not sure what to make of this either. The PAN ID
may change if a PAN ID conflict is detected, in which
case it would be a nuisance if all of the interface IDs
had to change. To me, the only time where it might make
sense to to use the PAN ID in the interface ID would be
if a lowpan was spread across multiple PANs that did not
coordinate 16-bit address assignment. Even in that case,
it would be better to use a 'symbolic' PAN ID in the
interface IDs, to avoid the need to change later.
In a lowpan With only a single PAN ID it makes much more
sense to use zeros and avoid problems if the PAN ID has to
change.
-Richard Kelsey
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