On 07/12/10 04:47 AM, Zach Shelby wrote:
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.
What happens when the 6LBR later needs to advertise a second prefix?
Does it first have to emit ABROs with Context flag= false and wait for
some unknown amount of time until the implicit CID=0 information is no
longer used? It clearly doesn't want to retire the PIO by setting its
Valid Lifetime to zero.
Perhaps something like the above can be made to work, at the cost of
more complex implementation in the hosts and routers and with some
operational constraints on when and how a 2nd prefix can be added to the
network.
Question is how to compare that added complexity with the savings of
bytes on the wire. My takes is less complexity wins in this case.
Erik
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