TU Wien:Verteilte Systeme VO (Dustdar)/Pruefung 2013-12-02

Unterschied symmetric und asymmetric Cryptography

Symmetric: the same key is used for encryption and decryption

Asymmetric: en- and decryption key differ, but form a pair

Was sind die Vorteile von Replication oder so ca.

More replicas can serve more client requests and replicas close the the client improves response time / reduces bandwidth

Benenne 3 Modelle/Patterns von Kommunikation.

Types of communication:

• Persistent: A message has been submitted for transmission, which is then stored by the middleware as long as it takes to deliver it to the receiver
• Transient: A message is stored by the system as long as the sending and receiving parties are both executing. If the message cannot be successfully delivered, the message is simply discarded.
• Asynchronous: Sender continues immediately after a message is sent and is interrupted once a response has been sent.
• Synchronous: Sender and receiver block for the duration of the communication

Communication models:

• Remote procedure call
• Message-oriented communication
• Stream-oriented communication
• Multicast

Was ist ein Socket?

A communication end point to/from which an application can send or receive data through the underlying network

Was ist ein Verteiltes System?

A collection of independent computers that appears to its users as a single coherent system

Nenne Gründe wieso man in unserer Zeit immer mehr Verteilte Systeme benötigt? (bin mir da nicht mehr ganz so sicher)

Distributed systems are growing in necessity as the amount of electronically stored information increases. Furthermore, the amount of networked devices is also growing and communication and easy (and efficient) access to data is required. Devices are also growing more mobile and are not always guaranteed to have connectivity, meaning protocols and models are necessary to cope with these changes. There are also new challenges in computing requirements as the amount of data increases that require multiple computers working in unison to tackle large computational problems.

Lamports Logical Clock bei einer gegebenen Kommunikation zwischen 2 Prozessen aufschreiben

Page 244 in book

Christians Algorithmus anwenden auf eine Serverzeit mit gegebenem RTT. Man musste die aktuelle Zeit vom Client berechnen die er dann haben sollte

Page 240 in book

2 Methoden wie man Scalability erreichen kann neben Replication

Hiding communication latencies (Async. comm, reduce overall comm)

Distribution (Hierarchies, domains, zones -> split)

Die Attribute zu Dependability und Security

Dependability:

• Availability: Immediate readiness for correct service
• Reliability: Continuity of correct service
• Safety: Absence of catastrophic consequences
• Integrity: Absence of improper system alterations
• Maintainability: Ability to undergo modifications

Security:

• Confidentiality
• Integrity

Was muss ein stateful Server bei clientseitigem Cachen speichern? Ca so.

The server must save a callback promise for a specific client. When the client has a file saved in the local cache, it must check to make sure that the server has a valid callback promise for the file. If the promise has been invalidated because another process accessed the file, changed it and reuploaded it to the server, then the cache that the first client has is no longer valid.

Quelle

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