System models

Architectural models #

Architectural models define functions of components and how they interact (cummunication).

Examples:

• Producer/consumer model
• Pipeline model (generalization of producer/consumer)
• Client/server model
• Peer-to-peer model

Fundamental models #

Abstracts views of system characteristics that affect correctness, reliability and security

• Interaction models
  • Synchronous
    • known upper bound on message delay
    • known clock drift
    • upper/lower bounds on the time a process needs to execute a step
  • Asynchronous: no timing assumptions!
• Failure models
  • Processes: faulty if its behavior deviates from that prescribed by the algorithm, otherwise, it is correct
  • Communication

Two Army Problem #

Questions:

• Which general leads the attack?
• At which point in time to attack?

Solutions (under synchronous assumption):

• No lost messagers (fixed amount possible): select leader on total ordering,
• If messengers can be captured (i.e. communication failure): use acknowledgements that are periodically send until received