Robert Assimiti a écrit :
Hello Alex. I think this definition needs to be revised in order to
accommodate not only the context of a 802.15.4 PAN but also the
context of wireless subnets in general.
I agree. The definition in question is the following:
LoWPAN Link
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.
At least the formulation "link shared by a link-local scope" is
confusing. Maybe a "link connecting nodes which are part of the same
link-local scope"(?)
Then it says "broadcast over the air in a route over LoWPAN" which is
less understandable again...
Then there are more definitions which are less understandable. The
Route Over is some of the less clear:
Mesh Under
A LoWPAN configuration where the link-local scope is defined by
the boundaries of the LoWPAN and includes all nodes within.
Forwarding and multihop routing functions are achieved at L2
between mesh nodes.
Route Over
A LoWPAN configuration where the link-local scope is defined by
those nodes reachable over a single radio transmission.
What is a single radio transmission? Is it that non-link-local scope
implies several radio transmissions?
Due to the time-varying characteristics of wireless communication,
the neighbor set may change over time even when nodes maintain the
same physical locations.
Excuse-me but I really don't understand this: time-varying
characteristics of wireless communications - do you mean TDD?
> Route Over [...] Multihop is achieved using IP routing.
Multihop with IP routing means also that the router forwards between two
different links (each with its own link-local scope). However, the
"Route Over" definition above uses a single link-local scope.
I'll write separately about mesh under.
Alex
-----Original Message----- From: Alexandru Petrescu
[mailto:[email protected]] Sent: Wednesday, April 22, 2009
11:13 AM To: Robert Assimiti Cc: [email protected] Subject: Re:
[6loWPAN] 6loWPAN Design and Application Spaces for 6loWPANs - 02-
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*
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