Subject: [6tsch] cell load balancing and 6tus monitoring

From: Thomas Watteyne <[email-masked]>
Date: Thu, 23 May 2013 11:53:19 -0700

Qin, all,

Xavi raises an interesting point about load balancing. [1] describes how
6tus can trigger a soft link maintenance procedure by using "traffic load
statistics" on the soft cells in a bundle. Slide 8 in [2] indicates that
this can be for example done by comparing the PDR of the different cells in
a bundle.

Does this mean that, for being able to compare all cells of a bundle need
to be used the same number of time?

Thomas

[1] http://tools.ietf.org/html/draft-wang-6tsch-6tus-00#section-2.8
[2]
https://bitbucket.org/6tsch/ietf86-orlando/src/2fb6792bd0f9ada8356bdc0df56f61e053551493/wednesday/05-draft-wang-6tsch-6tus-00.ppt?at=master

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From: "Qin Wang" <[email-masked]>
Date: Fri, 24 May 2013 02:49:58 -0700

Hi Thomas,

In the 6tus monitoring, there are two kinds of factors being monitored.

One is "cell quality", which may trigger soft cell maintenance procedure,
i.e. replacing the bad cell with a new cell.

Another one is "traffic load". For a given bundle, the average length of
its queue can be used to indicate traffic load on the bundle, which may
trigger a soft cell Reservation process or a soft cell Remove process,
i.e. adding more cells or deleting some cells.

Thought?

Qin

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From: Thomas Watteyne <[email-masked]>
Date: Fri, 24 May 2013 19:05:49 -0700

Qin,

I like the idea of using the traffic load on a bundle to trigger
adding/removing cells. Some hysteresis might be needed to avoid
instability, though. I don't know whether you had any ideas on the type of
algorithm for that?

The point I was trying to make in my previous e-mail is that, if you use
the cell quality to trigger a reschedule of a bad cell, you need to be able
to compare apples to apples. This might require you to have all cells used
pretty much the same amount of times, which might in turn require some form
of load balancing across the several cells in a bundle. If you choose to do
this, you will for sure have worse latency and buffering.

We discussed this on the ML, and the general feeling was that this might
not be a real problem at this point. We agreed to keep this in mind if we
stumbled across a related problem in the future.

Thomas