Distributed
Systems
Architectures
IS301 – Software Engineering
Lecture # 15 – 2004-10-04
M. E. Kabay, PhD, CISSP
Assoc. Prof. Information Assurance
Division of Business & Management, Norwich University
mailto:[email protected]
V: 802.479.7937
1
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Objectives
 To explain the advantages and disadvantages
of different distributed systems architectures
 To discuss client-server and distributed
object architectures
 To describe object request brokers and the
principles underlying the CORBA standards
 To introduce peer-to-peer and serviceoriented architectures as new models of
distributed computing.
2
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Topics covered
 Multiprocessor architectures
 Client-server architectures
 Distributed object architectures
 Inter-organizational computing
Today we will use 27
of Prof. Sommerville’s
slides in class
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Distributed systems
 Virtually all large computer-based systems
are now distributed systems.
 Information processing is distributed over
several computers rather than confined to a
single machine.
 Distributed software engineering is therefore
very important for enterprise computing
systems.
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System types
 Personal systems that are not distributed and
that are designed to run on a personal
computer or workstation.
 Embedded systems that run on a single
processor or on an integrated group of
processors.
 Distributed systems where the system
software runs on a loosely integrated group
of cooperating processors linked by a
network.
5
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Distributed system
characteristics
 Resource sharing
Sharing of hardware and software resources.
 Openness
Use of equipment and software from different
vendors.
 Concurrency
Concurrent processing to enhance performance.
 Scalability
Increased throughput by adding new resources.
 Fault tolerance
The ability to continue in operation after a fault
has occurred.
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Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Distributed system
disadvantages
 Complexity
Typically, distributed systems are more
complex than centralized systems.
 Security
More susceptible to external attack.
 Manageability
More effort required for system
management.
 Unpredictability
Unpredictable responses depending on the
system organization and network load.
7
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Distributed systems
architectures
 Client-server architectures
Distributed services which are called on by
clients. Servers that provide services are
treated differently from clients that use
services.
 Distributed object architectures
No distinction between clients and servers.
Any object on the system may provide and
use services from other objects.
8
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Middleware
 Software that manages and supports the
different components of a distributed system.
In essence, it sits in the middle of the system.
 Middleware is usually off-the-shelf rather than
specially written software.
 Examples
Transaction processing monitors;
Data converters;
Communication controllers.
9
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Multiprocessor architectures
 Simplest distributed system model.
 System composed of multiple processes
which may (but need not) execute on different
processors.
 Architectural model of many large real-time
systems.
 Distribution of process to processor may be
pre-ordered or may be under the control of a
dispatcher.
10
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
A multiprocessor traffic
control system
Sensor
processor
Sensor
contr ol
process
Tr aff ic flow
processor
Display
process
Tr aff ic light cont r ol
processor
Light
contr ol
process
Tr aff ic light s
Trafficflowsensorsand
cam er as
11
Opera tor c onsoles
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Client-server architectures
 The application is modeled as a set of
services that are provided by servers and a
set of clients that use these services.
 Clients know of servers but servers need not
know of clients.
 Clients and servers are logical processes
 The mapping of processors to processes is
not necessarily 1 : 1.
12
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
A client-server system
c3
c2
c4
c1 2
c1 1
Ser v er p ro ce ss
s4
s1
c1
c1 0
c5
Clien t pr o cess
s2
c6
c7
13
s3
c9
c8
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Computers in a C/S network
c1
CC1
c2
CC2
c3 , c4
CC3
Net wo rk
s1, s2
s3, s4
SC2
Ser v er
co m pu ter
SC1
Clien t
co m pu ter
c5 , c6 , c 7
c8 , c9
CC4
14
CC5
c1 0 , c1 1 , c1 2
CC6
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Application layers
16
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Thin and fat clients
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A client-server ATM system
AT M
AT M
Account ser ve r
Teleprocessing
m onit or
Cust om er
account
dat abase
AT M
AT M
21
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A 3-tier C/S architecture
23
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An internet banking system
Client
Client
HT T P int erac tion
Dat abase ser ver
W eb server
S QL query
Account ser vice
provision
S QL
Client
Client
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Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Cust om er
account
dat abase
Distributed object
architecture
o1
o2
S ( o1)
o3
S ( o2)
o4
S ( o3)
S ( o4)
Object request br oker
o5
S ( o5)
27
o6
S ( o6)
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
A data mining system
Dat abase 1
Re por t gen.
I nt eg r ator 1
Dat abase 2
Visualiser
I nt eg r ator 2
Dat abase 3
Display
30
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
CORBA application structure
Applic ation
object s
Dom ain
f acilities
Horizonta l C OR BA
f acilities
Object request br oker
COR BA ser vice s
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Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
ORB-based object
communications
o2
o1
S ( o1 )
S ( o2 )
IDL
stub
IDL
skelet o n
Object Requ est Br ok er
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Inter-ORB communications
o1
o2
o3
o4
S ( o1)
S ( o2)
S ( o3)
S ( o4)
IDL
stub
I DL
skele ton
IDL
stub
IDL
skele ton
Object Request Br oker
Object Request Br oker
Net work
40
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Decentralized p2p
architecture
n4
n6
n8
n7
n2
n1 3
n1 2
n3
n1 3
n9
n1
45
n1 0
n1 1
n5
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Semi-centralized p2p
architecture
Disc over y
server
n4
n1
n3
n6
n5
n2
46
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
Web services
49
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Automotive system
53
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Homework
Names etc.
on upper
right, please
 Required
By 11 Oct 2004
For 20 points, answer in detail
12.3, 12.8 (@10) [use computer-drawn
diagrams for these two]
For 5 points, answer in detail 12.5
 Optional
By 18 Oct 2004
For a maximum of 8 additional points,
answer any or all of
12.1, 12.2, 12.4, 12.6 (@2)
56
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
DISCUSSION
57
Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.
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Distributed Systems Architectures