Hi Gabe,
I have some questions regarding the M bit in lowpan.
The draft says in pg 5:
The LoWPAN payload (e.g., an
IPv6 packet) follows this encapsulation header. Alternatively, if
the 'M' bit is on, before this actual payload, a "Final Destination"
field will be present (Section 9).
On pg 6
M: This bit is used to signal whether there is a "Final Destination"
field as used for ad hoc or mesh routing. If set to 1, a "Final
Destination" field precedes the IPv6 packet (Section 9).
Q1: What is meant by 'used for adhoc or mesh routing' ? I assume that it
means M bit is used for both control and data path for multihop routing -
is it correct?
If it's used for data routing in mesh-network, then I see why the draft
wanted to keep original MAC source address field unchanged. But I beleive
the MAC implementation sets its own MAC address anyway when it transmits
a packet. ( I don't know of all implementations though).
It seems if we can come up with a IEEE address format for lowpan, then
it can be compressed easily over a LowPAN network to include both
originator address and final address.
----------------------------------------
9. Packet Delivery in a Link-Layer Mesh
A device that wishes
to send a packet may, in such cases, use other intermediate devices
as forwarders towards the final destination. In order to achieve
such packet delivery using unicast, it is necessary to include the
final destination in addition to the hop-by-hop destination. This
final destination may be expressed either as a layer 2 or as an IP
(layer 3) address.
In the latter case, there is no need to provide any additional header
support in this document (i.e., at the sub-IP layer). The link-layer
destination address points to the next hop destination address while
the IP destination address points to the final destination (IP)
address (that may be multiple hops away from the source). Thus,
while forwarding data, the single-hop destination address changes
hop-by-hop pointing to the "best" next hop, while the destination IP
address remains unchanged.
----------------------------------------------
Does the above paragraph mean we could have M bit set and final destination
address could be a 16 byte IPv6 address?
I wonder why do we need IPv6 address
in M bit case? Shouldn't the final IP destination be extracted from the
IPv6 header in the payload? Not sure, what it means by 'any additional
header support'.
I wonder what is the need for supporting a L3 address in final destination
field (when it talks about packet delivery in the link-layer)?
Thanks,
-Samita
_______________________________________________
6lowpan mailing list
[email protected]
https://www1.ietf.org/mailman/listinfo/6lowpan
