University of Amsterdam, Distributed Systems1 Distributed Systems DOAS Marinus Maris

University of Amsterdam, Distributed Systems 1

Distributed Systems

DOAS

Marinus Maris


Centralized versus distributed systems

Centralized Distributed

device

Hostcomputer

device

device

devicedevice

device

Hostcomputer

device

device

devicedevice


Intelligent Distributed Systems

NID

NID

NID

NID NID

NID

Hostcomputer


Networked Intelligent Devices

Every sensor and actuator is equipped with local intelligence and a network connection

NIDs can:– Analayze their

environment– Communicate– Negotiate– Take decisions and

actions autonomously


Embedded

Systems

Smar

t

Senso

rs

Actuat

ors

NetworksAlgorit

hmsNIDs

To create distributed NID networks, synergie between technologies is required

NIDs


Typical NID architecture

Reactieve laag

Deductieve laag

Sensor/actuator

input output

Reactieve laag

Deductieve laag

Sensor/actuator

input output

NID1 NID2


Typical Distributed System Architecture

central


Why distributed?

Distributed monitoring and control enables:• Local intelligence, so fast and appropriate response• Good scalability• Hierarchical decomposition into sub-control groups. This

lowers the computational complexity since the groups need only partial knowledge

• Sub-groups can be optimized for space and (response) time

• Graceful degradation. Failure of one device won’t lead to total system failure.


Typical use: Robust Control Networks for complex systems

shipsships process industryprocess industry offshoreoffshore

• Increase the robustness of such control systems• Improve the reaction time in case of calamities• Reduce required manpower for emergency recovery


(Some) Distributed Intelligence Methods

• Rule Based• Fuzzy Logic• Neural Networks• Bayesian Networks • Gradient method• Demand-supply method


Example case: Chilled Water System on a Ship

Zone 2

Zone 1

users

seawater

seawater coolingfluid

coolingfluid

coolingwater

coolingwater

users


Decomposition into subsystems

Zee-water

1

Koel-middel

1

Koelwater

vóór

crossover

1

Koelwater

na

crossover

1

VIT1 NVIT1

Crossoverkoel-

middel

Crossoverkoelwater

Zee-water

2

Koel-middel

2

Koelwater

vóór

crossover

2

Koelwater

na

crossover

2

VIT2 NVIT2


Assign states to the subsystems

(voorbeelden)


Network Architecture

Ethernet

LonWorks

Sensorsand

actuators

Router Bridge

Ship ControlCenter

Hub


Method 1: Rule-based

• Knowledge of system is represented in rules, such as:

– if pipe leaks then close valves

Rules are simple however…• Difficult to maintain• So make a hierarchy of rules (e.g. define for each

subsystem a small set of rules):

– If koelmiddel1 defect then close it and open cross-over


2. Bayesian Network (voor probleem-analyse)


Adding evidence: “kleppenKW gesloten”


Adding evidence: “CoolingVIT1”=false

Waar zit nu de grootste kans op het defect


3. Gradient Method: Determines the shortest path in a network (in this case pipes)

Seawater (zone 1) Cooling fluid (zone 1) Cooling water (zone 1)

Cooling water (zone 2)Cooling fluid (zone 2)Seawater (zone 2)

VU11

1

4 8

14 19

181332 6

6 8 13 18

14 19

2 3 41

105

211

552211 1

552

1

11



VU11

1

4 8

14 19

181332 6

11 13 18 23

19 24

2 10 91

105

211

552211 1

552

1

11



VU11

1

14 19

181332

23 28

24 29

2 101

105

211

552211 1

552

1

11

20 189

4 86

• Scales very well• Cannot exploit multiple sources for cooling


4. Demand Supply Control Method

• Free market principle• Negotiation between suppliers and demanders• Cooling is the product• Priority determines which party will deliver the

product

• Scales well• Can exploit multiple sources• Due to the inertia of the medium (water) the lack of

cooling may be discovered rather late


Comparison Methods (chilled water system)


Hybrid Approach

Reactive layer

Deductive Layer

Rule-based

Demand-supply

Isolates defects

Exploits multiple sources

Creates a path betweensource and destination

Gradient method

All methods have their own specific advantages and drawbacks, so use a hybrid approach, for example:


Voorbeeld: Gebouw beveiliging “Compound security”

compound

buffer zone

hek

w eg

intelligentesensordevices

centralebew akings

post

pan/tilt/zoomcamera

onveiliggebied


Compound Security, User-interface

Node is (nog) niet actief

Node niet meer actief

Node actief, geen detectie

Node actief, detectie

Node actief, Geen detectie, voorheen wel detectie

Mogelijke toestanden:


Distributed Systems, general advantages

• Scalable• Quick response times• Lower communication bandwidth required• Robust (graceful degradation)• Autonomous decision making through negotiation• Reduces false alarm rate through combining

different sensor information• Low power requirements• Cheap• Quick and easy installation (sensors can be

thrown out)


Typical disadvantages / challenges

• Localization • Ad-hoc networking• Sensor-fusion • Security • Lower power• More computing power required per node • Communication and processing are more complex• The intelligence layer


A possible future….

Documents

University of Amsterdam, Distributed Systems1 Distributed Systems DOAS Marinus Maris