Hi Robert, let me give my oppinion on this.
Robert Assimiti a écrit :
Hello,
I was going over the second spin of Draft-IETF-6lowpan-usercases.
I am a bit unclear on the definition of the LoWPAN link. A LoWPAN Link
is coined as:
/“//A low-power wireless link which is shared by a link-local scope in a
LoWPAN. In a LoWPAN, a link can be a very instable set of nodes, for
instance the set of nodes that can receive a packet/
/that is broadcast over the air in a route over LoWPAN, or the set of
nodes currently reachable in an L2 mesh in a mesh under LoWPAN. Such a
set may vary from one packet to the next /
/as the nodes move or as the radio propagation conditions change.”/
It is clear that we are targeting point-to-point and point-to-multipoint
here, but there is nothing that indicates the directionality of the link.
I am not sure what you mean being clear we're targetting ptp and
pt-to-mpt links...
I am aware ROLL WG targets the point-to-multipoint types of traffic (not
the links).
I think 802.15.4 link may be a point-to-point link, or a 'star'
topology, which one may interpret as being a point-to-multipoint link.
Whereas I understand very well running IP over a point-to-point link, I
don't see how would it run over a point-to-multipoint link, never saw
this before.
As for the link-local scope mentioned in the paragraph above, I think it
comes from what a "link-local scope" is for link like an Ethernet link.
But, it is not clear at all what a link-local scope would be on a
802.15.4 star topology made of a point-to-multipoint link: would a
packet sent by the center reach all edges? Or only one? Would a packet
from an edge to another have a dst address the center or the edge? Two
dst addresses?
I prefer to think that a LoWPAN subnet is covered by an IP link-local
scope, has at least one single IPv6 subnet prefix; and that IP packets
addressed to a link-local IPv6 address reaches all nodes in the LoWPAN,
without being 'IP-forwarded'.
If such LoWPAN subnet sit on a 802.15.4 link then that 802.15.4 link
should offer link-layer multicast support to the LoWPAN subnet, such
that the words "link-local scope" to have a meaning for a 802.15.4-based
LoWPAN. This is not the case today.
Is the definition here (since it is a wireless context) considered
unidirectional or bi-directional?
This is a good question. I do suppose 6LoWPAN WG uses links which are
bidirectional and symmetric.
Alex
Also, the definition given in RFC4861 does not really apply here.
Thanks for anyone that could offer a clarification.
*"The nice thing about standards is that there are so many to choose
from." - Andrew S. Tanenbaum *
*Robert Assimiti*
*Executive Staff Engineer*
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