Chapter1:Introduction to
Distributed System
Topic of Contents
• Distributed systems
• Definitions,
• Basic Concepts,
• Examples
• Advantages Distributed systems
• Characteristics Distributed systems
• Challenges
System
• Definition
Collection of components that are organized for a common purpose.
Computer System
Education System
Human Body System,etc
History
Centralize System Characteristics
• Single Computer Resource to handle of request
• Single Computer Resource shared by users all the time
• All resources accessible by user all the time
• Software runs in a single process
• Single point of control
• Single point of failure
Distributed systems
• Definition
A distributed system consists of a collection of autonomous
computers, connected through a network and distribution middleware,
which enables computers to coordinate their activities and to share the
resources of the system, so that users perceive the system as a single,
integrated computing facility.
Why DS:Availibility of powerful yet cheap microprocessor,continue advancement in communication technology
Distributed systems Characteristics
• Multiple autonomous components
• Components are not shared by all users
• Resources may not be accessible
• Software runs in concurrent processes on different processors
• Multiple Points of control
• Multiple Points of failure
Examples of Distributed Systems
• Local Area Network and Intranet
• Database Management System
• ATM Network
• Internet/World-Wide Web
• Mobile Computing
• Cloud Computing
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DBMS:Examples of Distributed Systems
Automatic Teller Machine Network(ATM)
Advantage of Distributed System
• Resource Sharing :Ability to use any hardware, software or data anywhere in the system. .
• Scalability :More nodes can easily be added to the distributed system i.e. it can be scaled as required.
• Fault tolerant : Failure of one node does not lead to the failure of the entire distributed system. Other
nodes can still communicate with each other.
• Redundancy :Several machines can provide the same services, so if one is unavailable, work does not
stop.
• Openness : extensions and improvements of new component in distributed systems.
• Concurrency : Components in distributed systems are executed in concurrent processes.
• Transparency :Distributed systems should be perceived by users and application programmers as
a whole rather than as a collection of cooperating components.
Transparency
Transparency dimensions
Properties
Access Transparency
Enables local and remote information objects to be accessed using same
operations.
Location Transparency
Enables information objects to be accessed without knowledge of their
location.
Concurrency Transparency
Enables several processes to operate concurrently using shared information
objects without interference between them.
Replication Transparency
Enables multiple instances of information objects to be used to increase
reliability and performance without knowledge of the replicas by users
Failure Transparency
enable users and applications to complete their tasks despite the failure of
other components
Migration Transparency
Enable movement of information objects within a system without affecting the
operations of users or
Performance Transparency
Enable the system to be reconfigured to improve performance as loads vary.
Scaling Transparency
Enable the system and applications to expand in scale without change to the
system structure
Disadvantage of Distributed System
• It is difficult to provide security in distributed systems because the nodes as
well as the connections need to be secured.
• Some messages and data can be lost in the network while moving from one
node to another.
• The database connected to the distributed systems is difficult to handle as
compared to a single user system.
• Overloading may occur in the network if all the nodes of the distributed
system try to send data at once.
Challenges:
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Increased complexity:
Synchronization process challenges
Imperfect scalability:
More complex security
Increased opportunities for failure:
Communication
Software structure
System architecture
Workload allocation
Consistency maintenance