Fundemental Models Flashcards

1
Q

What are the 3 fundemental models?

A

Interaction Model
Failure Model
Security Model

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2
Q

What are the 3 bounded aspects for synchronous systems in the interaction model?

A

Time to execute processes
Time to deliver messages between processes
Drift of clock from real time.

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3
Q

What is drift?

A

The amount the physical clock of a system has changed from real time.
Inconsistencies between machines caused by clocks being updated by different frequencies.

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4
Q

What is jitter?

A

The variation in time taken to deliver a series of messages.

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5
Q

What are asynchronous systems better for than SS?

A

Modelling the internet and real systems.

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6
Q

How does the failure model handle failures?

A

Hiding: Process replication for process ommision, transmission for channel ommision.
Conversion: Corrupted messages can be identified by checksum and discarded, arbitary failures can be converted into channel ommision failures and hidden.

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7
Q

What are the requirements for reliable 1-1 communication? (2)

A

Validity: All sent messages eventually arrive
Integrity: A received messages is identical to the message that was sent.

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8
Q

How is integrity maintained in reliable 1-1 communication?

A

Checksums + retransmission + discarding of duplicate messages.

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9
Q

What are the goals of the security model? (2)

A

Protect objects and secure processes and their interactions.

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10
Q

What are the threats to processes? (2)

A

Id spoofing, malicious code.

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11
Q

What are the threats to channels?

A

Copy/alter/inject messages

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12
Q

What are the security techniques of the security model?

A

Cryptography: Encrytion of exchanged and stored data.
Authenitcation: Digital signatures.
Secure Channels: Authenticated parties. Prove integrity and privacy of transmitted data.

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