Post on 31-Mar-2015
University of Amsterdam, Distributed Systems 1
Distributed Systems
DOAS
Marinus Maris
University of Amsterdam, Distributed Systems 2
Centralized versus distributed systems
Centralized Distributed
device
Hostcomputer
device
device
devicedevice
device
Hostcomputer
device
device
devicedevice
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Intelligent Distributed Systems
NID
NID
NID
NID NID
NID
Hostcomputer
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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
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Embedded
Systems
Smar
t
Senso
rs
Actuat
ors
NetworksAlgorit
hmsNIDs
To create distributed NID networks, synergie between technologies is required
NIDs
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Typical NID architecture
Reactieve laag
Deductieve laag
Sensor/actuator
input output
Reactieve laag
Deductieve laag
Sensor/actuator
input output
NID1 NID2
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Typical Distributed System Architecture
central
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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.
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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
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(Some) Distributed Intelligence Methods
• Rule Based• Fuzzy Logic• Neural Networks• Bayesian Networks • Gradient method• Demand-supply method
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Example case: Chilled Water System on a Ship
Zone 2
Zone 1
users
seawater
seawater coolingfluid
coolingfluid
coolingwater
coolingwater
users
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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
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Assign states to the subsystems
(voorbeelden)
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Network Architecture
Ethernet
LonWorks
Sensorsand
actuators
Router Bridge
Ship ControlCenter
Hub
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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
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2. Bayesian Network (voor probleem-analyse)
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Adding evidence: “kleppenKW gesloten”
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Adding evidence: “CoolingVIT1”=false
Waar zit nu de grootste kans op het defect
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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
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
11 13 18 23
19 24
2 10 91
105
211
552211 1
552
1
11
Seawater (zone 1) Cooling fluid (zone 1) Cooling water (zone 1)
Cooling water (zone 2)Cooling fluid (zone 2)Seawater (zone 2)
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
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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
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Comparison Methods (chilled water system)
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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:
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Voorbeeld: Gebouw beveiliging “Compound security”
compound
buffer zone
hek
w eg
intelligentesensordevices
centralebew akings
post
pan/tilt/zoomcamera
onveiliggebied
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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:
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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)
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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
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A possible future….