I.1

1
Distributed Systems Prof. Dr. Alexander
Schill Dresden Technical University Computer
Networks Dept. http//www.rn.inf.tu-dresden.de
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Motivation and development tendencies

• Desktop PC
• multitasking
• networking
• direct manipulation, graphical interface
• high performance (CPU, transfer)
• large primary and secondary storage
• Areas of application
• management / development (CASE Computer Aided
  Software Engineering)
• team working (CSCW Computer Supported
  Collaborative Work)
• group communication
• process control (CIM Computer Integrated
  Manufacturing)

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Sample topology
LAN
WAN
L
V.A.N.
L
LAN (for instance high performance network)
Value added network
A
A
N
N
DistributedOS

• networked workstations, also organizationally
  integrated
• super-proportionally increasing communication
  performance

Distributed DB
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Distributed System

• physical computer nodes (processor storage)
• direct / indirect computer coupling
• local networks (Ethernet (CSMA/CD), Token Ring,
  Token Bus)
• high-performance networks (Gigabit Ethernet, ATM)
• gateways / bridges
• radio networks (GSM, UMTS)
• transport-oriented comm. protocols (TCP/IP,
  UDP/IP, IPng)
• communicating processes
• complete logical connection
• no complete physical connection (communication
  via inter-components)
• system oriented resources (file system, threads,
  system programs)
• distributed storage, decentralized, co-operative
• distributed applications (area specific) on top
  of distributed systems

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Example distributed application
LAN
WAN
L
V.A.N.
L
LAN for instance high performance network)
Value added network
A
A
N
N
DistributedOS
Logical communication path
Process
Distributed DB
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Distribution Purposes

• data, function and load distribution
• decentralization and co-operation
• locality properties and efficiency
• integration of partial applications
• remote resource access
• fault tolerance reliability and availability

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Application example
Client (for instance Point of Sale)
Server (for instance account server)
Server (for instance database)
Client (for instance Automated Teller Machine)
Requirements - decentralized system
structure - Internet/Intranet-integration - scal
ability - security concepts - transaction
processing - heterogeneity of systems
Client (for instance Home Access)
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Network infrastructure examples
ISDN / X.25Fast Ethernet / Token Ring
Client (for instance Point of Sale)
Fast Ethernet /Token Ring
Server (for instance account server)
Server (for instance database)
ATM
Client (for instance Automated Teller Machine)
X.25
Modem / ISDN / ADSLInternet-access

• required bridging between
• heterogeneous networks,
• system platforms and
• applications
• Middleware

Client (for instance Home Access)
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N-tier-architectures
Client (for instance Point of Sale)
Server (for instance account server)
Server (for instance database)
Client (for instance Automated Teller Machine)
Data management
Application logic
3-tier three-level structure preferable for
complex applications 2-tier two-level
structure (user-interface lt-gtHost) simpler,
but less flexible
Client (for instance Home Access)
User interface, if necessary pre-processing
(thin client vs.fat client)
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Middleware and Client/Server coordination
Application interaction
Object interaction
Def. of Middleware Infrastructure services for
distributed applications for bridging of
heterogeneity of different systems and networks
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Middleware Basic technologies
Java (Sun and others) - programming language,
applets - Remote Method Invocation (RMI) -
Enterprise JavaBeans (EJB) Components CORBA
(Common Object Request Broker Architecture) -
object-oriented, language independent relatively
low-level - standard of Object Management Group
(OMG) .NET / COM (Component Object Model) -
object-oriented, COM relatively proprietary,
.NET more open - development of
Microsoft Further approaches - MOM (Message
Oriented Middleware) - SOAP (Simple Object
Access Protocol), Web Services - transaction
monitors, Application Servers
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Middleware general overview
Application Server / Enterprise Appli- cation
Integration
Integrity
Usability by application developer
Component-Frameworks (CORBA, EnterpriseJavaBeans
, .NET, WebServices)
Transaction monitors Message Oriented Middleware
Object TransactionMonitor
Client/Server, Remote Procedure Call (RPC) (for
instance DCE - Distributed Computing Environment)
CORBA-/ RMI-/.NET/SOAP-Object-oriented Basic
comm.
Flexibility
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System models
Client/Server (Remote Procedure Call)
Client Call Result
Server Offered procedures
Control thread and data transfer
Separate address spaces
Object-oriented communication
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01
02
04
07
03
Computer 1
Computer 2
05
Computer 3
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provide document (Document 1)
Client A
Copy Document 1
generate index (Document 1)
Client B
Client C
provide document (Document 3)
Copy Document 3
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D1 Server.provideDocument (Document
1) D1.move (here) D1.ltoperationgt
Client-Object A
Document Server
Document 1
Document 1
D2 Server ... D2.generate Index ()
Document 2
Client-Object B
Document 2
. . .
Document n
Client-Object C
Document 3
D3 Server.provideDocument (Document
3) D3.ltoperationgt
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Comparison of system models
higher transparency grade and improved influence
on distribution with object-oriented model