[6lo] SCHC HC over IEEE 802.15.4: 2. Multihop route-over approaches

[Carles Gomez Montenegro <[e-mail]>]

Dear 6lo WG,

As you may have noticed, there are currently 3 approaches to enable
route-over multihop in draft-ietf-6lo-schc-15dot4. A preliminary analysis
of pros and cons of each one is provided in Appendix B of the draft, in -02
[1].

Summarizing:

- “Straightforward Route-Over” incurs the lowest header overhead, as it
only requires the SCHC Dispatch (1 byte). However, it is the most demanding
approach in terms of memory usage, since all network nodes (including
intermediate nodes) need to store all the Rules in use in the network.
Therefore, it will be suitable for rather static, small networks and/or
where nodes have sufficient memory.

- “Tunneled, RPL-based Route-Over” incurs greater header overhead (with
some cases in the order of 12-16 bytes, although it may be more depending
on e.g. the number of hops), but only the endpoints need to store Rules,
and only those Rules used for the end-to-end communications such endpoints
are involved in. It requires the use of RPL, in its non-storing mode.

- “Pointer-based Route-Over approach” also only requires the endpoints to
store the Rules they will need to communicate with other endpoints. The
header overhead contains a fixed 3-byte part and a variable one. The latter
depends on the kind of interactions between endpoints: a) in special cases,
it could be even zero, b) in intranetwork communication it could be 2-8
bytes (depending on how IPv6 addresses are built) and c) if interactions
with various possible external networks it could be up to 16 bytes. This
approach does not require the use of RPL, and is also compatible with RPL
storing mode.

There may be further subtleties to consider.

A question that has been raised is whether we might want to keep all three
route-over approaches in the document or reduce the number of such
approaches. As authors we are in favor of enabling all of them, since they
may be complementary, and the most suitable one can be chosen for each
deployment.

Thoughts? Would you have any preference?

Thanks,

Carles and Ana (document authors)

[1]
https://datatracker.ietf.org/doc/html/draft-ietf-6lo-schc-15dot4-02#name-analysis-of-route-over-mult