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CIS 505: Software Systems
Introduction to Distributed Systems
Insup Lee
Department of Computer and Information Science
University of Pennsylvania
CIS 505, Spring 2007
CIS 505, Spring 2007 Distributed Systems 2
Distributed Systems
๎˜Why distributed systems?
oavailability of powerful yet cheap microprocessors (PCs,
workstations, PDAs, embedded systems, etc.)
ocontinuing advances in communication technology
๎˜What is a distributed system?
oA distributed system is a collection of independent
computers that appear to the users of the system as a single
coherent system.
CIS 505, Spring 2007 Distributed Systems 3
Examples
๎˜The world wide web โ€“ information, resource
sharing
๎˜Clusters, Network of workstations
๎˜Distributed manufacturing system (e.g.,
automated assembly line)
๎˜Network of branch office computers -
Information system to handle automatic
processing of orders
๎˜Network of embedded systems
๎˜New Cell processor (PlayStation 3)
CIS 505, Spring 2007 Distributed Systems 4
Advantages and disadvantages
๎˜Advantages
oEconomics
oSpeed
oInherent distribution
oReliability
oIncremental growth
๎˜Disadvantages
oSoftware
oNetwork
oMore components to fail
oSecurity
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1

Introduction to Distributed Systems CIS 505: Software Systems

Insup Lee

Department of Computer and Information Science

University of Pennsylvania

CIS 505, Spring 2007

CIS 505, Spring 2007

Distributed Systems

2

 Distributed Systems

Why distributed systems?

o availability of powerful yet cheap microprocessors (PCs, workstations, PDAs, embedded systems, etc.)

o continuing advances in communication technology

What is a distributed system?

o A distributed system is a collection of independent coherent system.computers that appear to the users of the system as a single

CIS 505, Spring 2007

Distributed Systems

3

Examples

sharingThe world wide web โ€“ information, resource

Clusters, Network of workstations

automated assembly line)Distributed manufacturing system (e.g.,

processing of ordersInformation system to handle automaticNetwork of branch office computers -

Network of embedded systems

New Cell processor (PlayStation 3)

CIS 505, Spring 2007

Distributed Systems

4

Advantages and disadvantages

Advantages

o Incremental growtho Reliabilityo Inherent distributiono Speedo Economics

Disadvantages

o Securityo More components to failo Networko Software

CIS 505, Spring 2007

Distributed Systems

5

Organization of a Distributed System

Note that the middleware layer extends over multiple machines. A distributed system organized as middleware.

CIS 505, Spring 2007

Distributed Systems

6

Goals of Distributed Systems

Transparency

Openness

Reliability

Performance

Scalability

CIS 505, Spring 2007

Distributed Systems

7

Transparency

appear as a single computer.how to make a collection of computersHow to achieve the single-system image, i.e.,

2) at a lower level, make the system look1) hide the distribution from usersachieved at two levels:well as the application programs can beHiding all the distribution from the users as

transparent to programs.

1) and 2) requires uniform interfaces such as access

to files, communication.

CIS 505, Spring 2007

Distributed Systems

8

Transparency in a Distributed System

Different forms of transparency in a distributed system.

Hide whether a (software) resource is in memory or on disk

Persistence

Hide the failure and recovery of a resource

Failure

usersHide that a resource may be shared by several competitive

Concurrency

usersHide that a resource may be shared by several competitive

Replication

in useHide that a resource may be moved to another location while

Relocation

Hide that a resource may move to another location

Migration

Hide where a resource is located

Location

accessedHide differences in data representation and how a resource is

Access

Description

Transparency

CIS 505, Spring 2007

Distributed Systems

13

Scalability Problems

 Characteristics of decentralized algorithms:

the system state.No machine has complete information about

local information.Machines make decisions based only on

algorithm.Failure of one machine does not ruin the

clock exists.There is no implicit assumption that a global

CIS 505, Spring 2007

Distributed Systems

14

Scaling Techniques (1)

a) The difference between letting:

a server or

b)

a client check forms as they are being filled

CIS 505, Spring 2007

Distributed Systems

15

Scaling Techniques (2)

An example of dividing the DNS name space into zones.

CIS 505, Spring 2007

Distributed Systems

16

Pitfalls when Developing Distributed Systems

 False assumptions made by first time developer:

The network is reliable.

The network is secure.

The network is homogeneous.

The topology does not change.

Latency is zero.

Bandwidth is infinite.

Transport cost is zero.

There is one administrator.

CIS 505, Spring 2007

Distributed Systems

17

Hardware Concepts

computer systems: multiprocessors vs. multicomputersDifferent basic organizations and memories in distributed

CIS 505, Spring 2007

Distributed Systems

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Multiprocessors (1)

A bus-based multiprocessor

o Cache memory, hit rate, coherence, write-through

cache, snoopy cache

CIS 505, Spring 2007

Distributed Systems

19

Multiprocessors (2)

a)

A crossbar switch

b)

An omega switching network

CIS 505, Spring 2007

Distributed Systems

20

Homogeneous Multicomputer Systems

a)

Grid

b)

Hypercube

Tightly coupled vs. loosely coupled

CIS 505, Spring 2007

Distributed Systems

25

Types of Distributed Systems

Distributed Computing Systems

Distributed information systems

Distributed Pervasive/Embedded Systems

CIS 505, Spring 2007

Distributed Systems

26

Cluster Computing Systems

Figure 1-6. An example of a cluster computing system.

CIS 505, Spring 2007

Distributed Systems

27

Grid Computing Systems

systems.Figure 1-7. A layered architecture for grid computing

CIS 505, Spring 2007

Distributed Systems

28

Transaction Processing Systems (1)

Figure 1-8. Example primitives for transactions.

CIS 505, Spring 2007

Distributed Systems

29

Transaction Processing Systems (2)

 Characteristic properties of transactions:

transaction happens indivisibly.Atomic: To the outside world, the

violate system invariants.Consistent: The transaction does not

interfere with each other.Isolated: Concurrent transactions do not

the changes are permanent.Durable: Once a transaction commits,

CIS 505, Spring 2007

Distributed Systems

30

Transaction Processing Systems (3)

Figure 1-9. A nested transaction.

CIS 505, Spring 2007

Distributed Systems

31

Enterprise Application Integration

enterprise application integration.Figure 1-11. Middleware as a communication facilitator in

CIS 505, Spring 2007

Distributed Systems

32

Distributed Pervasive Systems

 Requirements for pervasive systems

Embrace contextual changes.

Encourage ad hoc composition.

Recognize sharing as the default.

CIS 505, Spring 2007

Distributed Systems

37

Desired Trends

Volume &

Diversity Quality &

Unit cost Usability

Maintenance

cost

CIS 505, Spring 2007

Distributed Systems

38

Electronic Health Care Systems (1)

 Questions to be addressed for health care systems:

stored?Where and how should monitored data be

How can we prevent loss of crucial data?

propagate alerts?What infrastructure is needed to generate and

How can physicians provide online feedback?

system be realized?How can extreme robustness of the monitoring

proper policies be enforced?What are the security issues and how can the

CIS 505, Spring 2007

Distributed Systems

39

Electronic Health Care Systems (2)

health care system, using (a) a local hub orFigure 1-12. Monitoring a person in a pervasive electronic

(b) a continuous wireless connection.

CIS 505, Spring 2007

Distributed Systems

40

Background: Sensor Networks

Types of sensors

o Seismic, low sampling rate magnetic, thermal, visual, infrared, acoustic and radar

Conditions to monitor

o Temperature, humidity, (vehicular) movement, lightning condition, pressure, soil makeup, noise levels

o Current characteristics such as speed, direction, and size of ano Mechanical stress levels on attached objectso Presence or absence of certain kinds of objects object

CIS 505, Spring 2007

Distributed Systems

41

Technology Trends: Mote Evolution

CIS 505, Spring 2007

Distributed Systems

42

SN Characteristics

Environment

o connect to physical environment (large numbers, dense, real-time)

o Sensor nodes are prone to failures, non-deterministic

o wireless communication

o massively parallel interfaces (to users and applications)

o management critical)Limited resources: battery, bandwidth, memory, CPU (power

Network

o Topology changes dynamically

o sporadic connectivity

o new resources entering/leaving

o large amounts of redundancy

o self-configure/re-configure

CIS 505, Spring 2007

Distributed Systems

43

SN applications

Infrastructure security, military applications

Environmental and Habitat monitoring

Health applications

Smart space/home applications

Other commercial applications

o Interactive museumso Traffic Control, vehicle tracking and detectiono Industrial Sensing

CIS 505, Spring 2007

Distributed Systems

44

Smart Spaces

Smart School

Smart City

Smart Factory

โ€ข Other Applications

Battlefields/Surveillance

Earthquake areas

Environmental Monitoring

Airport security

Emergency Response

Location Services