Gabriel,
You are correct that you can use prot_type to allow extensibility above
both the mesh and fragmentation layer. However, I was trying to get at
extensibility at layers between the mesh and fragmentation. IPv6
suggests that hop-by-hop options (e.g. a sequence number for
broadcast/multicast) and routing headers (for source route) should come
after addressing but before fragmentation. If these hop-by-hop/routing
headers help determine how a packet is routed, then this allows
individual fragments to be routed without having to do any form a
reassembly at each hop and without requiring nodes to keep state for a
stream of IP packet fragments. This advantage could be especially useful
for mesh networks with memory constrained devices. It was unclear to us
how you would support such functionality cleanly in the current 6lowpan
format because the prot_type field turns into the datagram_offset field
in subsequent fragments.
Does that clear things up a bit?
--
Jonathan Hui
[EMAIL PROTECTED]
gabriel montenegro wrote:
Jonathan,
I'm confused by your paragraph below. I'm not sure what you mean by
this. The prot_type field disappearing in subsequent packets has no
bearing on extensibility as I understand it. For example, if you were
to in the future decide to carry, say, RNP ("random network protocol")
over the current lowpan encapsulation, you'd have a prot_type value
assigned for RNP. This would allow you to send RNP over lowpan even if
you had a mesh configuration underneath (the mesh delivery header being
a general lowpan layer service), or if your RNP packets were large
(by using the fragmentation service, again a general lowpan layer
service). If a receiving station were to receive, say, a fragment
for an packet, it might not be able to know that it is RNP until
more fragments arrive. But it wouldn't be able to do anything until
the entire RNP packet arrives anyways. Just like in IPv4 or v6
fragmentation.
Or did you have something else in mind?
tnx,
-gabriel
----- Original Message ----
In the current 6lowpan proposal, the prot_type field disappears in
packets that are subsequent fragments. Thus, the prot_type field in the
current proposal only allows extensibility in upper layer protocols and
possibly in packets that do not require fragmentation. In the current
6lowpan proposal it wasn't clear to us how a new mesh protocol that
wanted to add a field to the header would do so in a clean way. Also,
what we were trying to convey with the "piggybacking" capability with
the stacked headers was that it was possible, not that we should promote
it.
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