Subject: [Roll] Does LLN node in the goal host set have to be ROOT?

From: Joakim Eriksson <[email-masked]>
Date: Tue, 01 Jun 2010 18:27:57 +0200

Hello,

I have assumed that it is possible to have a DODAG where some of the
nodes in the DODAG are part of the application-defined set of hosts
that needs to be reached (Goal). But reading the below section in
5.3.3.2 it might not be possible:

   "An LLN node that is a goal for the Objective Function is the root of
    its own grounded DODAG, at rank ROOT_RANK."

Is this a MUST requirement - or just a MAY?

Two examples:

1. Assuming that I have one node that store data on a SD card but has
a small amount of storage for route-entries. One working solution for
the DODAG would be something like this:

    ROOT -- [The rest of the DODAG]
    /
Storage
  node

In this case the Storage node will not need to store any route entries
and not need to route for other nodes. In fact, it might be a RPL-host.

2. Assuming that I have multiple nodes in the LLN that will all end up
in the same DODAG and that all of them are important for the application
to work. In this case only one of these will be the root and the other
would be routers / hosts in the DODAG. This is not possible with the
above requirement (in 5.3.3.2).

My feeling is that it would be ok to have more than one LLN node in the
"Goal" defined by the application. Am I missing some critical issue?

Best regards,
-- Joakim Eriksson, SICS