Re: [Roll] DIS for given parent in draft-thubert-roll-eliding-dio-information

[Rahul Jadhav <[e-mail]>]

Please find my comments below.

On Thu, 21 Nov 2019 at 09:03, Li Zhao (liz3) <[e-mail]> wrote:
>
> Hello Rahul,
>
> Node can store preferred parent's info when outage.

[RJ] Storing parent info in persistent storage seems costly. But let's
go with this premise for this discussion.

> But after reboot, it still need DIO from this parent to confirm whether this parent is alive. Because parent may be outage too.

[RJ] In case of outage if the child node sends multicast DIS with the
parent address, the parent node itself may not have attached to the
network and may be still trying. So the DIS may have to be repeated
till the point where parent node is attached as well. All the other
nodes would be trying to do the same with their DIS as well.

> Reset trickle timer can let parent inform all children and accelerate the network recovery. Otherwise, all nodes need to run unicast DIS request and unicast DIO response. It wastes too much of time.

[RJ] If we let the trickle time reset then we wouldn't be solving the
problem. Let me give an example:
a. Assume 20 nodes using parent P
b. there's an outage
c. all 20 nodes sending DIS(with P address) and resetting P's trickle timer.
P keeps on resetting the trickle because of high child density and
never is able to dole out DIO.

>
> Does it make sense?

[RJ] It is good to know the options assuming that the preferred parent
is stored in persistent storage. But making design choices based on
this (use of storage) assumption may not be the right way. Note that
there could be multiple preferred parents and the parent info is much
more dynamic and thus may require frequent updates to persistent
storage.

>
> Best regards,
> Li
>
>
> On 2019/11/20, 11:52, "Roll on behalf of Rahul Jadhav" <[e-mail] on behalf of [e-mail]> wrote:
>
>     Thanks Li for elaborating.
>
>     Regarding the warm boot use-case you mentioned, the nodes certainly do
>     not know whether they have individually rebooted or rebooted because
>     of mass-outage.
>     What I don't get is, if the child node already knows who the parent is
>     why would it want to reset its Trickle timer?
>
>     On Wed, 20 Nov 2019 at 11:31, Li Zhao (liz3) <[e-mail]> wrote:
>     >
>     > Hello Rahul,
>     >
>     > This is about " we need other nodes sending DIS to backoff on hearing other node's DIS ".
>     > The use case is for warm boot case when hundreds of nodes power outage at the same time.
>     > 1. Child nodes send DIS to inform given parent to reset its trickle. (unicast or multicast DIS both work)
>     > 2. Child nodes suppress or backoff sibling nodes' DIS. Only multicast DIS works.
>     >     And we need enhance Solicited Information option to identify this kind of DIS.
>     >
>     >
>     > Best regards,
>     > Li
>     >
>     > On 2019/11/19, 18:20, "Roll on behalf of Rahul Jadhav" <[e-mail] on behalf of [e-mail]> wrote:
>     >
>     >     Hi Li,
>     >
>     >     What is the use-case where the child node needs to inform the parent
>     >     to reset its trickle unilaterally when it already knows the parent's
>     >     address?
>     >     Please find my comments below.
>     >
>     >     Best,
>     >     Rahul
>     >
>     >     On Tue, 19 Nov 2019 at 13:34, Li Zhao (liz3) <[e-mail]> wrote:
>     >     >
>     >     > Hello all,
>     >     >
>     >     >
>     >     >
>     >     > As we discussed today, there is a requirement that node sends out multicast DIS to only reset given parent’s Trickle.
>     >
>     >     [RJ] We discussed today that we need other nodes sending DIS to
>     >     backoff on hearing other node's DIS. We also discussed that we need
>     >     parent node to not keep on resetting the trickle timer all the time on
>     >     hearing DIS.
>     >     I am not sure we discussed about sending a multicast DIS to reset a
>     >     given parent's Trickle. Or may be I didn't get it correctly. Can you
>     >     please elaborate? Thanks
>     >
>     >     >
>     >     >
>     >     >
>     >     > Can we enhance Solicited Information option to add a flag to identify given parent’s address as following?
>     >     >
>     >     >
>     >     >
>     >     >         0                   1                   2                   3
>     >     >
>     >     >         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>     >     >
>     >     >        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>     >     >
>     >     >        |   Type = 0x07 |Opt Length = 19| RPLInstanceID |V|I|D|P| Flags |
>     >     >
>     >     >        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>     >     >
>     >     >        |                                                               |
>     >     >
>     >     >        +                                                               +
>     >     >
>     >     >        |                                                               |
>     >     >
>     >     >        +                            DODAGID                            +
>     >     >
>     >     >        |                                                               |
>     >     >
>     >     >        +                                                               +
>     >     >
>     >     >        |                                                               |
>     >     >
>     >     >        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>     >     >
>     >     >        |Version Number | Parent Address     (16bytes)                  |
>     >     >
>     >     >        +-+-+-+-+-+-+-+-+                                               +
>     >     >
>     >     >        +                                                               +
>     >     >
>     >     >        |                                                               |
>     >     >
>     >     >        +                                                               +
>     >     >
>     >     >        |                -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>     >     >
>     >     >        +-+-+-+-+-+-+-+-+
>     >     >
>     >     >
>     >     >
>     >     > P flag: One Bit, indicates DIS request response from given parent
>     >     >
>     >     >
>     >     >
>     >     >
>     >     >
>     >     > Best regards,
>     >     >
>     >     > Li
>     >     >
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