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Design Challenges to Construct Distributed System
Ajaykumar.M.V
IT Department
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The following are the Challenges to construct distributed system
1. Heterogeneity
2. Openness
3. Security
4. Scalability
5. Failure handling
6. Concurrency
7. Transparency
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1. Heterogeneity
Variety and difference-Networks, computer hardware, OS, Programming language
– solutions: middleware is needed (i.e. corba), mobile code, virtual machines •Networks
–Ethernet, token ring, etc•Computer hardware
–big endian / little endian•Operating systems
–different API of Unix and Windows•Programming languages
–different representations for data structures•Implementations from different developers
–no application standards
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• Middleware– applies to a software layer that provides a programming
abstraction as well as masking the heterogeneity of the underlying networks, hardware, OSs and programming languages
– CORBA(common object request broker architecture)– Java RMI(remote method invocation)
• Mobile code– is used to refer to code that can be sent from one computer to
another and run at the destination.– Ex) Java applet: JVM(java virtual machine) provides an abstract
a way of making code executable on any hardware
Heterogeneity… continued
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2. Openness
– extended and re-implemented in various ways
• Openness of a computer system -- is the characteristic that determines whether the system
can be extended and re-implemented in various way. e.g. Unix
• Openness of distributed systems -- is determined by the degree to witch new resource sharing services can be added and be made available for
use by A variety of client programs.e.g. Web
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3. Security
1. Confidentiality• protection against disclosure to unauthorized
individuals,
2. Integrity• protection against alteration or corruption, e.g.
checksum• Cryptography can enhance confidentiality &
integrity3. Availability
• protection against interference with the means to access the resources, • e.g. Denial of service• Security of mobile code
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4. Scalability
– effective with significant increase in resources – cost and performance• A system is described as scalable
– if will remain effective when there is a significant increase in the number of resources and the number of users
• A scalable example system: the Internet
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5.Failure handlingIn the domain of network & server
How to deal with partial failures?Techniques for failure handling1.Detecting Failures : some failures can be detected
•e.g. checksums can be used to detect corrupted data in a message or a file.
2.Masking Failures : some failures that have been detected ,can be hidden.
two examples of hiding failures* messages can be retransmitted when they fail to
arrive.* file data can be written to pair of disks so that if
one is corrupted, they other may still be correct.3. Tolerating Failures :- ignore, timeout
•e.g. a web browser cannot contact a web server
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4. Recovery Failures : Recovery involves the design of software so that the state of permanent data can be recovered or rollback after a server has crashed.• e.g. Roll back
5. Redundancy in hardware/software service can be made available by the use of redundant
components.
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6. Concurrency
• Both services and applications provide resources that can be shared by client in a distributed system.
• Correctness– ensure the operations on shared resource correct in a
concurrent environment
• Performance– Ensure the high performance of concurrent operations
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7. Transparency• how to make a collection of computers appear as a
single computer.
• Hiding all the distribution from the users as well as the application programs.
• Transparency is defined as the concealment from the user and the application programmer of the separation of components in a distributed system.
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7. Transparency
1. Access Transparency2. Location Transparency3. Concurrency Transparency4. Replication Transparency5. Failure Transparency6. Mobility Transparency7. Performance Transparency8. Scaling Transparency
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1. Access Transparency
• enables local and remote resources to be accessed using identical operations
• Example: SQL Queries • Example: File system operations in NFS.
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2. Location Transparency
• enables resources to be accessed without knowledge of their physical or network location.
• Example: pages in the web• Example: File system operations in NFS• Example: Tables in distributed databases
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3. Concurrency Transparency
• enables several processes to operate concurrently using shared resources without interference between them
• Example: NFS• Example: Automatic teller machine network• Example: Database management system
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4. 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.
• Example: Distributed DBMS• Example: Mirroring Web Pages.
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5. Failure Transparency
• enables the concealment of faults, allowing users and application programs to complete their tasks despite the failure of hardware or software components.
• e.g., email
• Example: Database Management System
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6.Mobility Transparency
• allows the movement of resources and clients within a system without affecting the operation of users or programs.
• Example: NFS• Example: Web Pages• Example: mobile phone
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7 .Performance Transparency
• Allows the system to be reconfigured to improve performance as loads vary.
• Example: Distributed make.
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8. Scaling Transparency
• Allows the system and applications to expand in scale without change to the system structure or the application algorithms.
• Example: World-Wide-Web• Example: Distributed Database
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Thank You