SpeckZone Formation and Maintenance in Specknets

About This Presentation

Title:

Description:

Number of Views:18

Avg rating:3.0/5.0

Slides: 22

Provided by: Andr909

Category:

Tags: speckzone | formation | kilobytes | maintenance | specknets

Transcript and Presenter's Notes

Title: SpeckZone Formation and Maintenance in Specknets

1
SpeckZone Formation and Maintenance in Specknets

2
Overview

3
The need for speckZones

An individual speck does not have enough memory
or processing power to be useful.
We can only run very simple programs in a few
Kilobytes of memory.
It is impossible to route between thousands of
individual specks with the current memory
constraint.
An individual speck moves around, is unreliable
and spends a lot of its time sleeping.

4
The need for speckZones

5
The need for speckZones

We can now program a speckZone rather than an
individual speck.
This gives us increased memory, processing power
and reliability.
We only have to route messages between a few
hundred zones rather than a few thousand
individual specks.

6
Constraints for the speckZone algorithm

The algorithm should be fully decentralised.
It should not rely on a single speck to manage
each speckZone, as specks are unreliable.
Synchronisation should not be required.
The speckZone must continue to operate if some of
its specks move away or run out of power.
The size of the speckZone must be maintained
despite the unreliability and mobility of specks.

7
The algorithm

The algorithm is decentralised, leaderless and
uses only local information.
Each speck has a state (or colour) that is
initially random.
Specks exchange colour information with their
one-hop neighbours.
If more than half of the surrounding specks have
a different colour from a given speck, that speck
will change colour.
The new colour is chosen according to the
distribution of colour in the local area.
Specks like to be the same colour as most of
their neighbours.

8
Simulation (sparse network)
9
Simulation (dense network)
10
A good speckZone

SpeckZones will have an optimum size
Large zones have more memory/processing power.
But if the zone is too large, it will be
expensive to manage.
The members of a zone should be close together
to reduce power required for communications
within the zone.
Applications that require a large amount of
communication between the zone may benefit from a
large surface area along zone boundaries.

11
Controlling the size of a speckZone

As we have just seen, there is a relationship
between the density of the network and the
natural size of the zones.
The density of the network determines the average
number of one-hop neighbours.
Using position information from Ryans Algorithm,
we can control the number of one-hop neighbours
and therefore the size of the zone.

12
Controlling the size of a speckZone

Specks start with a communication range of zero.
If the zone size is below the specified minimum,
the communication range is increased.
If the zone size is above the specified maximum,
the communication radius is reduced.
The amount of alteration is proportional to the
difference between the required and actual zone
size.

13
Preventing zones becoming too large

Before a speck changes state, it must check if it
will make the new zone too large. If so, it
should not change state.
If we have a maximum zone size of 20, the blue
speck must not change to green, as this would
create one large zone.
If the zone is too large, the specks on the edge
of the zone should change state with an increased
probability.

14
Counting the number of specks in a zone

15
The simple counting method

Each speck periodically sends a message
containing its ID and a sequence number.
Specks store these ID, sequence number pairs
and broadcast them on every iteration of the
algorithm.
Any specks that have not been heard from for a
few iterations are removed from the zone count.
A disadvantage of this approach is that messages
must be sent when there are no changes in the
zone.

16
The efficient counting method

Only changes to the members of a zone are
broadcast throughout the zone.
This significantly reduces the amount of
information that is sent in static networks.
If a new speck joins a zone, a message saying
that it has been added propagates throughout the
zone.
When a speck leaves the zone, a message saying
that it has left propagates throughout the zone.

17
Joining and leaving zones

When a speck changes state, it must
Inform the old zone that it has left (if
possible)
Inform the new zone that it has joined
If a speck does not hear from a neighbouring
speck for a few iterations, it should broadcast a
message advising that the neighbouring speck has
left the zone.
If a speck receives a message saying that it
should be removed from the zone, it must still be
in the zone.

18
Maintaining accuracy when specks leave a zone

A will now over-estimate the zone size at 3, as
it thinks C and D are still in the zone.
When B is removed, any other specks whos only
source is B should also be removed (C and D in
this case).

19
Simulation (controlling the zone size)