Subject: [6tsch] Re: Resend in HTML: Re: TSCH with multiple DAGroots

From: Tom Phinney <[email-masked]>
Date: Thu, 14 Feb 2013 15:25:27 -0700

Qin,

Your question implies a misunderstanding. Nodes do not HAVE slot
durations; nodes USE slot durations. A node that uses duocast for a
specific class of transmissions (e.g., 4 Hz process state publishing)
uses unicast or broadcast for all remaining transactions.

Existing industrial systems that use duocast employ duocast only for
state reporting for high-speed control loops. Those devices are, in the
absence of router failure, just one hop off the backbone, which is
typical for similar-usage devices in WirelessHART systems. Emerson and
Honeywell and other vendors of such high-loop-rate control devices agree
that one-hop placement is needed in most cases to support the control
requirements of the underlying process.

Unicast and broadcast are used by all the other nodes in that system for
all messaging, and by the nodes that use duocast for messaging needs
other than high-frequency process state publishing where delivery
reliability per transmission attempt is paramount.

FYI, I was one of the designers of both WirelessHART and ANSI/ISA
100.11a, and have had these discussions with the other designers of each
protocol.

-Tom
=====

On 2013.02.14 15:06, Qin Wang wrote:
> Hi Tom,
>
> Thank you for your explanation. It is very clear.
>
> I have one further question: Is there any constraint or assumption for
> nodes with different slot duration? For example, the nodes with different
> slot duration should belong to different DL network, or.....
>
> Thanks
> Qin

---

From: "Qin Wang" <[email-masked]>
Date: Thu, 14 Feb 2013 15:18:43 -0800

Tom,

I understand the application scenario you described. My concern is that it
is challenge for DL to deal with multiple slot durations simultaneously,
especially if collision-free is required. How do you think?

Qin

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