Subject: [6tisch] OTF allocation policies

From: Nicola Accettura <[email-masked]>
Date: Thu, 20 Mar 2014 21:21:00 +0100

Dear all,
after reading again all the discussions on the ML about pre-allocation,
post-allocation and hybrid allocation in OTF, I found that it could be
possible to include all these possibilities by introducing a Threshold
parameter. In this case, distinguishing among pre, post, hybrid would be
redundant, thus some terminology simplification can be obtained in the OTF
draft.

Considering the default Bandwidth Estimation Algorithm in OTF, there are
two conditions that can trigger a change in the bundle size:

1. if [outgoing - (incoming+self) < 0] is true: add some outgoing cells,
depending on the allocation policy
2. if [outgoing - (incoming+self) > 0] is true: delete some outgoing cells,
depending on the allocation policy

The specific allocation policy is used to delete or add cells. This means
that if 1. is true, cells could also not be added, depending on the
allocation policy. A similar reasoning can be done for 2.

Let's introduce a configurable positive THRESHOLD value. The previous
conditions become:

1. if [outgoing - (incoming+self) < -THRESHOLD] is true: add X outgoing
cells
2. if [outgoing - (incoming+self) > THRESHOLD] is true: delete X outgoing
cells

where X is strictly related to the value [outgoing - (incoming+self)
+THRESHOLD] and Y is strictly related to the value [outgoing -
(incoming+self) -THRESHOLD].

In this new version, a THRESHOLD beforehand set to 0 translates in a pure
post-allocation policy. Otherwise, the allocation policy is hybrid.
Actually, a pure pre-allocation policy would imply that cells are allocated
once for all in advance, without the possibility to enlarge or decrease the
bundle size.

In some way, the threshold introduces hysteresis, thus reducing requests
for adding/deleting cells. In addition, the threshold value can be a fixed
parameter or a variable that would depend on the standard deviation of the
traffic or on the difference between avarage and peak traffic.

These are only thoughts aiming to simplify (or complicate?) the draft
terminology.
What do you think?

Cheers
Nicola

---

From: Thomas Watteyne <[email-masked]>
Date: Sun, 23 Mar 2014 23:43:25 -0700

Nicola,
+1 on the idea of adding some hysteresis. We don't want a system operating
at the equilibrium point to constantly add/remove a cell.

Diego,
What do you think of the idea of removing the concepts of pre- and
post-allocation by a more homogeneous view such as the one proposed by
Nicola?

Thomas

On Thu, Mar 20, 2014 at 1:21 PM, Nicola Accettura
<[email-masked]>wrote:

> 2. if [outgoing - (incoming+self) > 0] is true: delete some outgoing
> cells, depending on the allocation policy
>
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