Hi all,
To be sure I understand: is the lowpan link concept different from the link
definition in IPv6?
link - a communication facility or medium over which nodes can
communicate at the link layer, i.e., the layer
immediately below IP. Examples are Ethernets (simple
or bridged), PPP links, X.25, Frame Relay, or ATM
networks as well as Internet-layer (or higher-layer)
"tunnels", such as tunnels over IPv4 or IPv6 itself.
Best,
Julien
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Alexandru Petrescu
Sent: jeudi 23 avril 2009 15:53
To: Robert Assimiti
Cc: [email protected]
Subject: Re: [6lowpan] [6loWPAN] 6loWPAN Design and Application Spaces for
6loWPANs - 02-
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*
>>
>> *Executive Staff Engineer*
>>
>> *Office: [678]-202-6859*
>>
>> *Mobile: [404]-578-0205*
>>
>> *[email protected]*
>>
>>
>>
>>
>>
>>
>>
>>
>>
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