As I said previously, I have difficulty understanding some terms in the
usecases draft.
For example, it defines LoWPAN Host, LoWPAN Router and LoWPAN Node.
However it doesn't say a LoWPAN Node may be a LoWPAN Host or a LoWPAN
Router. (I think, commonly in IPv6, Nodes may be Host or Routers).
It defines Mesh Under and Route Over; however I can't understand the
following: does a "Route-Over" LoWPAN contain the same IP link-local
scope or not? If yes then this is very difficult to udnerstand, next to
impossible.
Also, another problem is that it defines the Route-Over and Mesh-Under
in apple-to-orange terms ("boundaries" vs "radio range"), whereas
Route-Over and Mesh-Under have often been easily compared, ie
redapples-to-greenapples.
Then on the use of 'single radio transmission' to define "Route Over" -
what is single radio transmission more precisely? One is tempted to
believe all nodes reachable by a single radio transmission from a
certain node are all within the same IP link-local scope... which is ok.
Route Over
A LoWPAN configuration where the link-local scope is defined by
those nodes reachable over a single radio transmission. [...]
But because it doesn't say from _where_ are those nodes reachable (from
another single certain node) then one can easily also think this: B is
within a single radio transmission of both C and A, yet it is in two
different link-local scopes, which is of course not the intention.
-----------------------
|radiorange|radiorange|
A B C
Knowing the above, I'm trying to offer my own definitions of terms in
the way I'd have written it. Of course it may not fit all the views,
but I thought I'd share:
PHY repeating
The act performed by a device repeating a packet at PHY level. It
doesn't inspect any field in any packet header. It has one or several
interfaces, they are all in the same IP link-local scope.
MAC forwarding
The act performed by a bridge - inspecting the dst MAC address of
incoming packet, exact-matching it to the first field in a table of
tuples [dst,nexthop]
MAC addresses and transmitting it to the identified nexthop. In the
process, the src and dst MAC address of the packet are potentially
modified. The device may have one or more interfaces but they are all
in the same IP link-local scope.
IP routing
The act performed by a router - inspecting the dst
IP address of an incoming packet,
longest-prefix matching it to the first field of each entry
in a table of triolets
[dst,prefixlength,nexthop] IP addresses and transmitting it to the
identified nexthop. In the process, neither the src nor the dst IP
addresses of the packet are ever modified. It has two ore more
interfaces, each interface of the router has a different IP link-local
scope.
IP link-local scope
The set of IP nodes reachable by an IP packet whose dst address starts
with 0xff02. All nodes on a link are within the same IP link-local
scope, and nodes outside the link are outside the scope. Transmitting
packets in the same link-local scope doesn't involve IP routing but
may involve MAC forwarding.
Radio range of node
The radio range of a node is the set of nodes reachable from it, at
PHY layer. For example, the radio range of a WiFi node is 50m in a
clear-sight atmospheric area, without physical obstacles and in good
weather.
Obviously, all nodes in same radio range of a node could be understood
to be in the same IP link-local scope.
However, a single-interface node can't be part of several IP
link-local scopes even if sits at the intersection of the radio ranges
of several other nodes.
"Mesh-Under" LoWPAN
A LoWPAN configuration where the IP link-local scope is extended to
more nodes (beyond the radio range of a node) by means of MAC
forwarding exclusively. All nodes in a "Mesh-Under" LoWPAN are within
the same IP link-local scope, despite the probable presence of several
PHY radio ranges - this alleviates the non-transitivity aspect.
"Route-Over" LoWPAN
A LoWPAN configuration where the IP link-local scope is extended to
more nodes (beyond the radio range of a node) by means of transmitting
IP packets, using a novel IP routing method. This novel method
runs on a LoWPAN Router (uses a single interface, instead of the
typical 2-interface router) and both interfaces are in the same IP
link-local scope (instead of the typical router having a different IP
link-local scope for each interface).
"Routed" LoWPAN
A LoWPAN configuration where the IP link-local scope is not extended
beyond the radio range. Certain nodes are manually designated as
special. The radio range of each special node contains the set of
nodes in the same IP link-local scope, and each such range forms a
unique link. Connecting two such links is performed by means of a
typical IP router (multiple interfaces, different link-local scope).
Comments anyone?
Alex
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