Subject: [Roll] Upstream and downstream flows (was Unique destinations and the protocol survey draft)

From: <[email-masked]>
Date: Mon, 24 Nov 2008 11:18:54 +0100

I have had a couple of offlist exchanges with Phil on this issue.

Here is a reformulation of my concern.

Many LLNs are I think characterised by an asymmetry in the upstream and
downstream flows.
The upstream flows of many LLN applications are characterised by small
D.
However even for these applications the downstream flows do not
necessarily share this property.

Thus a criterion that applies to upstream does not necessarily apply to
downstream.

Madhu

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From: "Omprakash Gnawali" <[email-masked]>
Date: Mon, 24 Nov 2008 03:39:51 -0800

On Mon, Nov 24, 2008 at 2:18 AM,
<[email-masked]> wrote:
> The upstream flows of many LLN applications are characterised by small D.
> However even for these applications the downstream flows do not necessarily
> share this property.
>

In one of the research networks we have built and deployed for
structural health monitoring using accelerometers, we used
network-wide dissemination to command and control the sensors. The
instances when we had to command/control a single sensor were so few
and rare that we used network-wide dissemination and filter the
messages at higher layers to simulate a single destination for the
command and control. If D starts to become too large, perhaps the
system can switch to network-wide messaging to prevent D from becoming
too large and avoid having to store too much state. So, yes the
network could have a large number of unique destinations but that does
not necessarily imply a large number of destinations at the network
layer.

- om_p