Subject: [Roll] ROLL-NSA extension for PRE

From: Rahul Jadhav <[email-masked]>
Date: Sun, 24 Feb 2019 23:11:02 +0530

Hello All,

Following is my review of draft-ietf-roll-nsa-extension-00:

PRE could be an interesting technique that can be applied to subset of
traffic which is critical or requires low-latency. The draft talks
about extending NSA to send the node's parent-set in the DIO such that
the receiving child node could use this information to choose the
alternate paths appropriately.

1. Section 3 talks about three policies for alternative parent
selection. As i understand different nodes could use any of the
policies (strict, medium, relaxed) without having to worry about
interop. Also it will be optimum to choose strict policy followed by
medium and relaxed respectively. Is this correct?

2. Regarding compression, i didnt find a dispatch-like bit identifying
whether the PS addresses are compressed or not. Isn't it required for
the recipient to know whether the PS is compressed?

3. Most of the text is 6tisch specific and specifically says 6tisch
nodes whilst explaining the technique. I believe the technique is
generically applicable to non-6tisch scenarios as well. True?

4. I think a section on reparenting is needed. How would the child
node behave when its parent is reparenting? During reparenting, the
parent might send its updated DIO with its new parent set. The
implications of using CA strict policy in this case might result in
child choosing a different AP which certainly is not desirable if the
parent still has connectivity to its old parent and the reparenting is
done based on metric changes.

5. I am wondering if it is possible to attach a field "such as
min-priority [1]" field which is a derivative of the metric
calculation in context to every parent in the parent-set. This greatly
helps the child nodes in deciding the CA policy to use even though as
I understand that the parent-set is already attached in NSA in the
decreasing preference order.

Regards,
Rahul

[1] draft-richardson-6tisch-roll-enrollment-priority-01