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D7024E: DISTRIBUTED & MOBILE COMPUTING SYSTEMS
Lecture 01: Introduction to distributed and mobile computing. Architectural models for mobile & distributed computing systems.
Coulouris Dollimore and Kindberg
Characterization of Distributed Systems
Coulouris, Dollimore and KindbergDistributed Systems: Concepts and Design
Edition 4, © Pearson Education 2005
MDCS: What we will cover ?MDCS: What we will cover ?
Introduction to Distributed SystemsBird’s eye view on mobile/pervasive/wireless y /p /computing
Why mobile revolution is inevitableWhy mobile revolution is inevitableAdvanced applications for mobile computing
A hit t d t f di t ib t d tArchitectures and components of distributed systemsConcepts and terminology
D7024E MDCS: Introduction
Recommended ReferencesRecommended References
Coulouris, Dollimore, Kindberg, “Distributed Systems”, 4th Ed, Addison-Wesley, 2005
A. Tanenbaum, Van Steen, “Distributed Systems”, Pearson, 2007A. Tanenbaum, Van Steen, Distributed Systems , Pearson, 2007
T.Imielinski, H. Korth “Mobile Computing”, Kluwer Academic publishers, 1996
G. Forman & J. Zahorjan “The challenges of mobile computing”, IEEE Computer, April 1994, pp.38-47
Deitel H Deitel P Nieto T Steinbuhler K "Wireless Internet & Mobile Deitel, H, Deitel, P., Nieto, T., Steinbuhler, K. Wireless Internet & Mobile business", Prentice Hall, 2001, ISBN 0-13-062226-5
D7024E MDCS: Introduction
What is a True Distributed SystemWhat is a True Distributed System
“A system that runs on a collection of machines that do not have shared memory, yet looks to its y, yusers like a single computer”
Eg Amoeba, Sprite, Chorus, CloudsSingle set of System calls on each nodeSingle set of System calls on each nodeAll machines run the same kernelMachines communicateEach kernel controls its own resources (?)
Definition of a Distributed System (2)Definition of a Distributed System (2)
Figure 1-1. A distributed system organized as middleware. The middleware layer extends over multiple machines, and offers each application the same interface
Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5
same interface.
Figure 1.1A typical portion of the Internet
intranet
ISP
backbone
desktop computer:
satellite link
server:network link:
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 1.2A typical intranet
Desktopemail server pcomputers
print and other servers
email server
Web serverLocal areanetwork
email serverprint
th t f
File server
other servers
the rest of
router/firewall
the Internet
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
What is a Distributed Mobile Computing System
M bil i i i d M bil i i i d Mobile computing is associated Mobile computing is associated with mobility of with mobility of hardware, users, hardware, users, data and softwaredata and software in computer in computer ppapplications. applications. Specialised class of distributed Specialised class of distributed computing systems where some computing systems where some nodes can move in physical space, nodes can move in physical space, ad hocad hoc connecting/ disconnecting connecting/ disconnecting ad hocad hoc connecting/ disconnecting connecting/ disconnecting while remaining part of a while remaining part of a distributed system and perhaps distributed system and perhaps
ti i ti i l b l ti i ti i l b l participating in global participating in global computational activitiescomputational activities
Figure 1.3P bl d h dh ld d i i di ib d Portable and handheld devices in a distributed system
Internet
Host intranet Home intranetWAP Wireless LAN gateway
Mobilephone
LaptopPrinterCamera Host site
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 1.4Web servers and web browsers
BrowsersW b
www.google.comhttp://www.google.comlsearch?q=kindberg
Internet
BrowsersWeb servers
www.cdk3.nethttp://www.cdk3.net/
www.w3c.org
http://www.cdk3.net/
Protocols
A ti it ht l
http://www.w3c.org/Protocols/Activity.htmlFile system ofwww.w3c.org
Activity.html
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Cluster Computing SystemsCluster Computing Systems
Figure 1-6. An example of a cluster computing system.
Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5
Grid Computing SystemsGrid Computing Systems
Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5
Figure 1-7. A layered architecture for grid computing systems.
Figure 1.5Computers in the Internet
Date Computers Web servers
1979, Dec. 188 0
1989, July 130,000 01999, July 56,218,000 5,560,8662003, Jan. 171,638,297 35,424,956
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 1.6Computers vs. Web servers in the Internet
Date Computers Web servers Percentagep g
1993, July 1,776,000 130 0.008
1995 July 6 642 000 23 500 0 41995, July 6,642,000 23,500 0.41997, July 19,540,000 1,203,096 61999 July 56 218 000 6 598 697 121999, July 56,218,000 6,598,697 12
2001, July 125,888,197 31,299,592 2542,298,37142,298,371
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Th i l d t h llTh i l d t h llThe wireless data challengeThe wireless data challenge
To enable people to communicate/compute effortlessly, where they want, when they
want, without “Wires”
Mobile Computing: Problems and Assumptions
Location is dynamically changing informationCost of communication is asymmetricySevere power restrictions on mobile hostsLi it d t il bl bil h tLimited storage available on mobile hostsVolatility of information increases with the change of locationFrequent and foreseeable disconnectionsqSecurity issues due to mobility of hosts
Distributed Pervasive SystemsDistributed Pervasive Systems
Requirements for pervasive systemsRequirements for pervasive systems
• Embrace contextual changes.• Encourage ad hoc composition.Encourage ad hoc composition.• Recognize sharing as the default.
Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5
Pervasive computingPervasive computing
Th id th t t h l i i b d th l t tThe idea that technology is moving beyond the personal computer to everyday devices with embedded technology and connectivity as computing devices become progressively smaller and more powerful. Also called ubiquitous computing pervasive computing is the result ofcalled ubiquitous computing, pervasive computing is the result of computer technology advancing at exponential speeds ‐‐ a trend toward all man‐made and some natural products having hardware and software. Pervasive computing goes beyond the realm of personal computers: it isPervasive computing goes beyond the realm of personal computers: it is the idea that almost any device, from clothing to tools to appliances to cars to homes to the human body to your coffee mug, can be imbedded with chips to connect the device to an infinite network of other deviceswith chips to connect the device to an infinite network of other devices. The goal of pervasive computing, which combines current network technologies with wireless computing, voice recognition, Internet capability and artificial intelligence, is to create an environment wherecapability and artificial intelligence, is to create an environment where the connectivity of devices is embedded in such a way that the connectivity is unobtrusive and always available
http://www.webopedia.com/TERM/P/pervasive_computing.html
User ExpectationsUser Expectations
The user does not wish to beThe user does not wish to beconsidered exclusively as considered exclusively as Home Office
Ph
All-in-one device: convergence or divergence of applications?
considered exclusively as considered exclusively as a consumer.a consumer.
OfficeComputer
Phone
g g ppQuality of Experience: devices with intuitive, flexible, interactive and enabling interfaces, active guidance, personalised services, context awareness, price not an issue if the service proposition is compelling. Life assistant services: citizens wish to remain independent and mobile even in advanced Life assistant services: citizens wish to remain independent and mobile even in advanced years.Privacy safeguarding: requirements will increase in reaction to the growing possibilities of information interception and user profiling (location awareness and identity).Security technology: is demanded by users to cope with tracking services and Security technology: is demanded by users to cope with tracking services and surveillance systems
Challenges:Challenges:Bridging the gap from technological availability to actual market takeBridging the gap from technological availability to actual market take--upupBridging the gap from technological availability to actual market takeBridging the gap from technological availability to actual market take--upupCreating opportunities for userCreating opportunities for user--based innovationbased innovation
The following few slides are borrowed from J.DaSilva’s presentation at MDM’05, Cyprus, May, 2005
The world of Convergence
CECEMOBILEMOBILE BROADCASTBROADCASTBROADBANDBROADBAND
The world of Convergence
CECEPre-Recorded
ContentPersonal Media
MOBILEMOBILECommunication,Entertainment,
Pictures and Video
BROADCASTBROADCASTServices,
Entertainment
BROADBANDBROADBANDCommunication,Entertainment,
E-Business
Simple Networks Service Enabled Networks
Each island offers numerous Each island offers numerous services on distinct devicesservices on distinct devices
A converged archipelago offers A converged archipelago offers all services on all devicesall services on all devices
Challenges:Challenges:Providing endProviding end--toto--end service at minimal OPEX and CAPEXend service at minimal OPEX and CAPEXEnsuring the creation and management of convergenceEnsuring the creation and management of convergenceEnsuring the creation and management of convergenceEnsuring the creation and management of convergenceMoving from product supply to solution provisionMoving from product supply to solution provision
Services convergenceServices convergenceServices convergenceServices convergence
Anywhere
gamesgames
HDTVHDTVHome
gateway Any device
3
gamesgames
M bil
SatelliteSatellite
I i iMusic
AVprogram
ContentContent
3D TVComputerComputer Anytime
Mobileterminal
CableCableTerrestrialTerrestrial
Interactive serviceMultimedia
program
HDTVPC
Wired/wirelessWired/wireless3D A/V
DVB-H terminal
Networking convergenceNetworking convergence
DMBDVB-H (IP based core network) New radioNew radioNew radioNew radio
DTVDTV
Wire -linexDSL
Wire -linexDSL
CellularGSM-3G 4G WLAN
interfaceinterfaceinterfaceinterface
Satellite
T e le v is io n
B rid g eG a te w a y
WPAN
P D A Health sensor
C o m m . T o w e r
Home sensorL a p to p
P rin te r
V id e o
P D A
P D A
Cargo
Highway Nuclear
C o m m . T o w e r
C o m m . T o w e rP B X
C o m m . T o w e r
C o m m . T o w e r
Cargo sensor
River sensor
Bridge sensor
sensorOcean sensor
sensor
InteroperabilityInteroperability
At the Network/Device Level At the Network/Device Level Wireless/Mobile/Fixed/Cable/ISP/Broadcasting networks need to interoperate
At the Service/application LevelAt the Service/application LevelServices need to run across homogeneous or Services need to run across homogeneous or heterogeneous networks
At the Media/Content LevelAt the Media/Content LevelDiff t di f t t i tDifferent media formats must coexist
Challenges:Challenges:ggEnsuring smooth technological transitionsEnsuring smooth technological transitionsCreating opportunities for disruption and innovationCreating opportunities for disruption and innovationContributing to setting the right collaborative standardsContributing to setting the right collaborative standardsOptimising for innovation through a more agile IP regimeOptimising for innovation through a more agile IP regimeCoping with the trend towards the “patenting of software”Coping with the trend towards the “patenting of software”
Interoperability at Home
Internet, Music andInternet, Music and VoDVoD, Video, Video
PDAVideo walkman
Web TabletLaptop
Internet, Music and Internet, Music and TV/video everywhereTV/video everywhere
VoDVoD, Video , Video streaming, music streaming, music download, storagedownload, storage
Bluetooth andWi-Fi Phones
Users want their devices to work togetherand share contentHome Home
Media CentrePrinter
automation and automation and ControlControl
Media Centre
Game Console IP STB and PVRTeleworkTelework
Voice and video Voice and video conferencingconferencingTelemedicineTelemedicine
Challenges:Challenges:Ensuring content management interoperabilityEnsuring content management interoperabilitySt iki th i t b l b t i ht h ld d i htSt iki th i t b l b t i ht h ld d i htStriking the appropriate balance between right holders and consumers rightsStriking the appropriate balance between right holders and consumers rights
Explosion of Devices and DataExplosion of Devices and Data
Amount of data received or transmitted (in Petabytes/Day)
Information explosion and overload Information explosion and overload
Petabytes/Day)
1,000,000
1,200,000
IndustrialAutomobile
Number of communicating data Number of communicating data devices growing from 2.4 billion to 23 devices growing from 2.4 billion to 23 billion in 2008 and one trillion by 2012billion in 2008 and one trillion by 2012600,000
800,000
Automobile
Entertainment
billion in 2008 and one trillion by 2012billion in 2008 and one trillion by 2012
400,000
,Mobile
0
200,000
2003 2004 2005 2006 2007 2008
Computers
Challenges:Challenges:Designing and managing an information infrastructure where all devices communicate Designing and managing an information infrastructure where all devices communicate
ith d d t d thith d d t d th
2003 2004 2005 2006 2007 2008
with and understand one anotherwith and understand one anotherCreating an advanced digital ecoCreating an advanced digital eco--system for the agile enterprisesystem for the agile enterprise
The scale of networkingg
The wide area networks of The wide area networks of yesterday (eg: GSM)
> A Million nodes @ $50k
The Nomadic local area networks f d ( WiFi)of today (eg: WiFi)
> Millions of Nodes @ $100
The Sensor and Personal area network of tomorrow
@ $> Billions of Nodes @ $1Challenges:Challenges:
Removing social, geographical, economic and capacity Removing social, geographical, economic and capacity impediments impediments through the provision of through the provision of cost effective cost effective infrastructuresinfrastructures, allowing an “Always on” network existence., allowing an “Always on” network existence.Contributing to accrued facilities based competition.Contributing to accrued facilities based competition.
Ubiquitous computingUbiquitous computing
Suppose that you could get a 0 1$ “computer” Suppose that you could get a 0.1$ computer . What would you do with it?
Play, Work, Sense, ActuateC i t C t ACommunicate, Compute, AccessSearch for info, Find directionsExtend your perception of the worldT k t t d l tiTrack content and location
How would you configure it?In a stand alone mode I fi d k d iIn a fixed networked environmentIn ad-hoc networked environment
Should it be visible?How do you interface with it?How do you power it?
Content ExplosionNo shortage of content, either from private, corporate or public sourcesAggregation of content its structuring and indexing are key issuesExabyte (EB)
Content ExplosionAggregation of content, its structuring and indexing are key issuesFive exabytes of information is equivalent in size to the information contained in half a million new libraries the size of the Library of Congress print collections.
Exabyte (EB)1,000,000,000,000,000,000 bytes OR 10*18 bytes
2 Exabytes: Total volume of information generated in 1999.5 E b t All d k b h b i
% Change 1999-20001999-20002002 Terabytes2002 TerabytesStorage Medium
ScannedScanned CompressedCompressed
5 Exabytes: All words ever spoken by human beings.
Upper Estimates
Lower estimateUpper estimateLower estimateUpper estimate
36%2401,2003271,634Paper
-3%58,209431,69076,69420,254Film
80%2,073,7602,779,7603,416,2304,999,230Magnetic
69%69%2,132,2382,132,2383,212,7313,212,7313,416,2813,416,2815,421,2215,421,221TotalTotal
28%298151103Optical
36%2401,2003271,634Paper
Source: http://www.sims.berkeley.edu/research/projects/how-much-info-2003/printable_report.pdf Migrating to digital media
Wireless Evolution F Wireless Evolution Focus: UserUser--contentcontent
Focus: BandwidthBandwidth
Subscribers
Focus:
>QoE> Simplicity
> Performance
>Broadband
>New ServicesF
GrowthGrowth > Service Richness
>Security/trust
>Price
>EfficiencyFocus: CoverageCoverage
>Voice Quality >Scalability
>Ubiq it
>Coverage
>Mobility
>Portability
>Capacity
>Ubiquity
>Price
Voice
Mobile Ubiquitous NetworkingMobile Ubiquitous NetworkingUbiquitousUbiquitousMobile WorldMobile World
Broaden communication parties, networking, and business opportunities
Ubiquitous Ubiquitous WorldWorld
Networks with low performance devices(e.g. RF tags and sensors)
Mobile WorldMobile World
(Real World)
B3G Radio Access
B3G Mobile NetworkB3G Mobile Network
Networks with high performance Networks with high performance devices(e.g. home appliances)
Mobile NW Ubiquitous Local NW
Mobile EdgeMobile Edge
Mobile-Ubiquitous NW
Deep NetworkingSmall, inexpensive, lowSmall, inexpensive, low--powered sensors and actuators, deeply embedded into the physical powered sensors and actuators, deeply embedded into the physical
Deep Networking
environment in very large numbers, interacting and forming wired and wireless networks to environment in very large numbers, interacting and forming wired and wireless networks to communicate, adapt, act, respond, and coordinate highcommunicate, adapt, act, respond, and coordinate high--level tasks.level tasks. (e.g. Monitor the state of devices and provide necessary online diagnostics, maintenance support, etc.)
As these micro devices are networked the Internet will be pushed deeper than the current network As these micro devices are networked the Internet will be pushed deeper than the current network As these micro devices are networked, the Internet will be pushed deeper than the current network As these micro devices are networked, the Internet will be pushed deeper than the current network edge. This will enable a hundredfold increase in the size of the Internet.edge. This will enable a hundredfold increase in the size of the Internet.
Challenges:Challenges:New methods of networking devices to one another and to the Internet must New methods of networking devices to one another and to the Internet must b d l db d l dbe developed.be developed.
Smart dustSmart dust
D7024E MDCS: Introduction http://www-bsac.eecs.berkeley.edu/~warneke/SmartDust/index.html
Context aware devicesContext aware devices
Typical Mobile Computing ApplicationTypical Mobile Computing Application
DS: Challenges & design issues
TransparenciesTransparencies
•Access transparency: enables local and remote resources to be accessed using identicaloperations.•Location transparency: enables resources to be accessed without knowledge of their physical
t k l ti (f l hi h b ildi IP dd )or network location (for example, which building or IP address).•Concurrency transparency: enables several processes to operate concurrently using shared resources without interference between them.•Replication transparency: enables multiple instances of resources to be used to increase Replication transparency: enables multiple instances of resources to be used to increase reliability and performance without knowledge of the replicas by users or application programmers.•Failure transparency: enables the concealment of faults, allowing users and application programs to complete their tasks despite the failure of hardware or software components.•Mobility transparency: allows the movement of resources and clients within a system without affecting the operation of users or programs.P f t ll h b fi d i f •Performance transparency: allows the system to be reconfigured to improve performance as
loads vary.•Scaling transparency: allows the system and applications to expand in scale without change to the system structure or the application algorithms
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
the system structure or the application algorithms.
Architectural models & paradigms
D7024E MDCS: Introduction
Layered View on a Distributed System Layered View on a Distributed System
Applications & servicespp
DBMS, TPS, ...
Distributed OSMiddleware
m
Hardware Plat
form
Distributed Computing: System architecturesDistributed Computing: System architectures
The client/server modelPeer-to-peerpVariations to the 2 above
Figure 2.2Clients invoke individual servers
Client i ti Server
Server
Client invocation
result
Serverinvocation
resultServer
ClientClient
Process:Key:
Computer:
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.3A di ib d li i b d A distributed application based on peer processes
Peer 2
Application
ApplicationPeer 1
Application
Peer 3Sharableobjects
Peer 4
Peers 5 .... N
Application
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.4A service provided by multiple servers
Service
ServerServer
Client
Server
Client
Server
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.5Web proxy server
WebClient
Proxy
Web
server
server
server
Web Clientserver
Client
Caching
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.6Web applets) li t t lt i th d l di f l t da) client request results in the downloading of applet code
Web serverApplet code
Client
b) client interacts with the applet Mobile code
ClientWeb
AppletClient serverApplet
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.7Thin clients and compute servers
Network computer or PCCompute server
Thin Application
Network computer or PC
networkThinClient
ApplicationProcess
network
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
DS: Design IssuesDS: Design Issues
Must be transparentProvide flexibilityyHeterogeneityR li bilit /d d bilitReliability/dependabilityGood performanceSecurityScalableScalable
DS: ReliabilityDS: Reliability
Availability is a related factorDesign should not require the simultaneous g qfunctioning of a substantial number of critical componentspMore redundancy greater availability and greater inconsistencyinconsistencyFault tolerance, the ability to mask failures from the user
DS: Performance IssuesDS: Performance Issues
The rest are useless without thisHard to measure, benchmarks are meaningless, gBalance number of messages and grain size of distributed computationsdistributed computations
DS: ScalabilityDS: Scalability
A maxim for developing distributed systemsAvoid centralised components, tables and p ,algorithmsOnly decentralised algorithms should be usedOnly decentralised algorithms should be used
Scalability ProblemsScalability Problems
Figure 1-3. Examples of scalability limitations.
Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5
Scalability ProblemsScalability Problems
Characteristics of decentralized algorithms:No machine has complete information about the system state.Machines make decisions based only on local information.Failure of one machine does not ruin the algorithm.gThere is no implicit assumption that a global clock exists.
Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5
Pitfalls when Developing Distributed SystemsPitfalls when Developing Distributed Systems
False assumptions made by first time developer:The network is reliable.The network is secure.The network is homogeneous.gThe topology does not change.Latency is zeroLatency is zero.Bandwidth is infinite.Transport cost is zeroTransport cost is zero.There is one administrator.
Tanenbaum & Van Steen, Distributed Systems: Principles and Paradigms, 2e, (c) 2007 Prentice-Hall, Inc. All rights reserved. 0-13-239227-5
Fundamental models
D7024E MDCS: Introduction
Fundamental modelsFundamental models
InteractionSynchronousAsynchronousEvent orderingg
FailureS itSecurity
D7024E MDCS: Introduction
Figure 2.8Real-time ordering of events
d i isend receive
1 4X
receive
m2
m1
receive
send2 3Y Physical
time
receivem2
Zreceive receive
send
m1 m2A
m3
receive receive
Areceive receive receive
t1 t2 t3
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.9Processes and channels
process p process q
send receivem
Communication channel
Outgoing message buffer Incoming message buffer
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.10Omission and arbitrary failures
Class of failure Affects DescriptionFail-stop Process Process halts and remains halted. Other processes may
detect this state.Crash Process Process halts and remains halted. Other processes may
not be able to detect this state.Omission Channel A message inserted in an outgoing message buffer never
arrives at the other end’s incoming message buffer.Send-omission Process A process completes a send, but the message is not put
in its outgoing message buffer.R i i i P A i i ’ i i Receive-omission Process A message is put in a process’s incoming message
buffer, but that process does not receive it.Arbitrary(B ti )
Process orh l
Process/channel exhibits arbitrary behaviour: it mayd/t it bit t bit ti(Byzantine) channel send/transmit arbitrary messages at arbitrary times,
commit omissions; a process may stop or take anincorrect step.
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.11Timing failures
Class of Failure Affects DescriptionClock Process Process’s local clock exceeds the bounds on its
rate of drift from real time.Performance Process Process exceeds the bounds on the interval
bbetween two steps.Performance Channel A message’s transmission takes longer than the
stated bound.
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.12Objects and principals
invocationObjectAccess rights
resultClient
Serverresult
NetworkPrincipal (user) Principal (server)
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.13The enemy
Copy of m
The enemym’
Communication channelProcess p Process qm
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
Figure 2.14Secure channels
P i i lA PrincipalBPrincipal A
S h lP P
Principal B
Secure channelProcess p Process q
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4, © Pearson Education 2005
DMCS: ConclusionsDMCS: Conclusions
ArchitecturesConcepts and terminologyp gyProblems of distributed & mobile computingD i i i lDesign principles
What’s next ? - Enabling technologiesWhat s next ? Enabling technologies
Radio-based communicationsWireless LANsEtc