Zach Shelby a écrit :
[...]
Multicast with link-local scope, is simply a link-layer broadcast and is
not retransmitted.
I am not sure what you mean (in general? 802.15.4 in particular?) but
multicast with link-local scope maps into link-layer multicast, and is
not simply link-layer broadcast. Some link-layers do support link-layer
multicast and it is all an advantage to ND.
For example to each IP link-local multicast address corresponds a MAC
link-layer multicast address (like 33:33::1). Moreover, IPv6 stacks
simply don't work with link-layer addresses which use MAC broadcast
addresses (48 1 bits).
Alex
So the above does not occur. Thus this kind of
multicast used by RAs and NSs is not a big problem. We should still keep
the frequency of these down.
If you try to do a multicast with scope > 2, then you have a flooding
problem unless multicast is implemented in some other way. This is why
we use the Whiteboard approach in 6lowpan-nd, to avoid the need to flood
the LoWPAN.
Medium access control schemes of wireless link-layers are able to
deal with extra transmissions from multihop forwarding.
I agree MAC schemes could alleviate the B transmits back to A problems.
And these schemes are part (supposedly?) of the Mesh-Under concept.
Which makes think that Route-Over wouldn't work without Mesh-Under at
the same time.
This has nothing to do with mesh-under. Every wireless link-layer
implements medium access control, for example CSMA in the case of IEEE
802.15.4.
Of course because you are forwarding with a single interface, your
channel capacity decreases with more hops (this is the multihop
penalty of all such schemes, including Mesh Under).
Ok.
Otherwise nodes should have a means to know on _which_ link-local
scopes are they, and send data on only one scope. But I think
there's only one link-local address per interface, and only a
scope_id field in the respective C struct.
Not needed, the link-layer deals with this using MAC addressing and
the MAC algorithm. A node just tracks who are its neighbors.
Ok. Some questions rest about how does the link layer deal with
link-layer multicast addresses, when they are used by RS and NS, such
that to avoid noise amplification on non-transitive links.
You use link-local scope and it is not a problem (RS and NS are
link-local messages). You of course want to keep the amount of ND
signaling on a whole as low as possible - which is a goal of 6lowpan-nd.
Alex
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