Zach Shelby a écrit :
Hi,
Alexandru Petrescu wrote:
Zach Shelby a écrit :
Alex,
Alexandru Petrescu wrote:
one-interface routers and links (again)
Let me first describe one-interface routers as I understand are
proposed in 6LoWPAN:
+------------------------+---------------+ |
| | 2001:db8:1::1/128 2001:db8:1::2/128
2001:db8:1::3/128 _|eth0 _|eth0
_|eth0 |R1 | |R2 | |R3 | ---
--- ---
R1 sends an IP packet to R3 but this reaches only R2. R2 picks
the packet, looks at the dst address, finds it's not for self,
consults routing table, finds a host-based route and sends it
to R3. This can work ok.
Exactly, you pictured this nicely. This is how LoWPAN Routing
works. I'll get back to the definition of that in your other
thread.
Ok...
If we say the dashed line is The Link then we're in the ND case,
any node can talk to any other node at link-layer, no IP routing
throughout.
But if it is not The Link, and it is not two times The Link - then
what is it?
What is the link definition needing a LoWPAN single-interface IP
router?
The definition used in the other thread for a LoWPAN link, which in a
wireless network may be non-transient, I think covers this case.
The definition in the thread, inheriting from rfc4861 and other rfcs, is
_not_ a non-transitive link. That link is clearly defined as linking
all nodes in the medium: all nodes communicate at link-layer,
one-by-one, any node to any node:
link - a communication facility or medium over which
nodes can communicate at the link layer, i.e.,
the layer immediately below IP (each node can
communicate to each other in this medium).
Examples are Ethernets (simple or bridged), PPP
links, X.25, Frame Relay, wireless links or ATM
networks as well as Internet-layer (or
higher-layer) "tunnels", such as tunnels over
IPv4 or IPv6 itself.
This is a slightly modified definition of the link
defined in RFC4861, in order to cover also the wireless
links. Wireless links may be non-transitive (node A
communicates at link layer to both B and C yet B and C
are not on the same link). Hidden terminal problem in
wireless communications is described in [reference to
individual draft in AUTOCONF]
draft-baccelli-multi-hop-wireless-communication-02
This says that a wireless link is also a link. The fact that "wireless
link_s_ may be non-transitive" is alleviated by the fact that "link -
... each node can communicate to each other in this medium".
Maybe we shouldn't use "Wireless links" above but "Wireless media"
because "link" is the term being defined.
Because the link is non-transient R1 and R2 can communicate, R2 and
R3 can communicate, but R1 and R3 can't.
A 'non-transitive' link is different from the Link definition we
mentioned above, because nodes on that link can all communicate to each
other at link-layer. That Link is not non-transitive, it is transitive.
How would one define a 'non-transitive' link? As two serially connected
Links? This implies the middle router has two interfaces - which we
don't want.
So, what is the definition of a 'non-transitive' Link?
(I'm not sure how to explain this better, but we don't seem to agree).
Alex
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