Fundemental Models Flashcards
What are the 3 fundemental models?
Interaction Model
Failure Model
Security Model
What are the 3 bounded aspects for synchronous systems in the interaction model?
Time to execute processes
Time to deliver messages between processes
Drift of clock from real time.
What is drift?
The amount the physical clock of a system has changed from real time.
Inconsistencies between machines caused by clocks being updated by different frequencies.
What is jitter?
The variation in time taken to deliver a series of messages.
What are asynchronous systems better for than SS?
Modelling the internet and real systems.
How does the failure model handle failures?
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.
What are the requirements for reliable 1-1 communication? (2)
Validity: All sent messages eventually arrive
Integrity: A received messages is identical to the message that was sent.
How is integrity maintained in reliable 1-1 communication?
Checksums + retransmission + discarding of duplicate messages.
What are the goals of the security model? (2)
Protect objects and secure processes and their interactions.
What are the threats to processes? (2)
Id spoofing, malicious code.
What are the threats to channels?
Copy/alter/inject messages
What are the security techniques of the security model?
Cryptography: Encrytion of exchanged and stored data.
Authenitcation: Digital signatures.
Secure Channels: Authenticated parties. Prove integrity and privacy of transmitted data.
