18 - Middleware"Glue code between network operating system...

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Middleware • "Glue" code between network operating system and customer applications • In support of distributed heterogeneous computation • Similar in concept to architectural connectors
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Context • Growth of networked machines – Increasing customer base • Specialization of hardware resources • Increasingly powerful applications – Integration of existing components – Negotiation
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Needs • Abstractions – Interfaces (APIs) – Standards • Notations • Tools – Design – Code generation
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Characteristic Issues 1. Network communication 2. Coordination 3. Reliability 4. Scalability 5. Heterogeneity
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1. Network Communication • Data transport • Transactions (ACID) – A tomic (all or none) – C onsistency-preserving (database integrity) – I solated (other transactions can’t see intermediate states) – D urable (committed and persistent) • Error handling / reliable delivery
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Data Transportability marshalling, serialization • Bit order • Byte order • Character sets • Alignment • Word length • Organization (of constituent pieces) • Self definition (identity)
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2. Coordination • Synchronization Synchronous : client blocked while waiting for service Asynchronous : server initiated • Multicast (push) • Hardware stop/restart • Activation/deactivation (persistent state) • Server concurrency
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Concurrency Control • Session layer responsible for synchronization • Blocking (synchronous) • Non-blocking – Client (polling); deferred synchronization; pull – Server; asynchronous; push
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• Assurance policies (communication) – Best-effort – At-most-once – At-least-once – Exactly-once • Reliability/performance tradeoff • Replication
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This note was uploaded on 05/03/2010 for the course SA 5010 taught by Professor Spen during the Spring '10 term at Asian Institute of Management.

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18 - Middleware"Glue code between network operating system...

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