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Other models:

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Lecture 9 Other models: Monitoring models Reliability and fault-tolerance models Performance models. Scheduling policies. Security models – PowerPoint PPT presentation

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Title: Other models:


1
Lecture 9
  • Other models
  • Monitoring models
  • Reliability and fault-tolerance models
  • Performance models. Scheduling policies.
  • Security models

2
Student presentations and midterm
  • I expect a progress report the week after the
    Spring break (March 18 24).
  • The final project report is due the week before
    last.
  • Midterm two weeks from today
  • Material Chapters 1,2, and 3 up to the last
    lecture.
  • Open book.
  • 3 questions 30 minutes

3
Monitoring models
  • A monitor could be a process responsible to
    establish the global state of a System.
  • Intrusion Heissenbers uncertainty for quantum
    processes.
  • Run a total ordering of all events in the global
    history of a process.
  • Cut a subset of the local history of all
    processes.
  • Frontier of a cut the last event of every
    process in the cut.

4
Consistent and inconsistent cuts
  • Consistent cut a cut that agrees with causality.
  • Inconsistent cut violates causality.
  • Causal history of an event the smallest cut
    including the event.
  • The snapshot algorithm of Chandy and Lamport.
  • Checkpointing in parallel and distributed
    computing.

5
Consistent and inconsistent cuts
6
Causal history
7
The snapshot protocol (ChandyLamport)
8
Reliability and fault-tolerance models
  • A failure at time t is un undesirable event
    characterized by its
  • Manifestation incorrect timing or value of
    variables
  • Consistency the system may fail in a consistent
    or in an inconsistent state.
  • Effects benign/ malign
  • Occurrence mode singular or repeated

9
Failure modes for processes P and for
communication channels C
  • Crash - PC
  • FailStop - P
  • Send Omissions - P
  • Receive omissions - P
  • General omissions PC
  • Byzantine PC
  • Arbitrary with message authentication - P
  • Timing P

10
Collective communication
  • Broadcast and multicast.
  • Applications
  • Routing in mobile ad hoc networks.
  • Routing in the Internet to disseminate
    topological information flooding algorithms.
  • Used to achieve consensus.
  • Multicasting of audio and video streams to reduce
    the bandwidth.
  • Parallel algorithms barrier synchronization.

11
Collective communication
12
Properties of a broadcast algorithm (I)
  • Validity if a correct cc-process broadcasts a
    message m all correct cc-processes eventually
    deliver m.
  • Agreement - if a correct cc-process delivers
    message m all correct cc-processes eventually
    deliver m.
  • Integrity every correct cc-process delivers m
    once and only once and only if the message was
    broadcast by a cc-process

13
Properties of a broadcast algorithm (II)
  • FIFO order if a correct cc-process broadcasts a
    message m before m then no correct cc-processes
    delivers m unless it has previously delivered m.
  • Causal order - if a correct cc-process broadcasts
    m that causally precedes m then no correct
    cc-processes delivers m unless it has previously
    delivered m.
  • Total order if two correct cc-processes p and q
    both deliver messages m and m then p delivers m
    before m if and only if q delivers m before m.

14
Broadcast primitives and their relationships
15
Performance models
  • Resource sharing!!!
  • Arrival process distribution of inter-arrival
    times or arrival rates.
  • Service process distribution of service times
    or inter-departure times.
  • Number of servers
  • Quantities of interest
  • Time in system, T
  • Waiting time W
  • Number in system, N
  • Littles law N ? T

16
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17
Performance models
  • Types of systems
  • Deterministic D/D/1
  • Markov arrival, Markov service - M/M/1
  • Markov arrival, general service M/G/1
  • Batch arrival.
  • Server utilization ? ratio of arrival rate to
    service rate.
  • Stability ?lt 1 necessary but not sufficient
  • Time in system is finite
  • Number in system is finite

18
Performance models
  • When utilization tends to 1 ? time in system
    becomes unbounded.
  • Network congestion.

19
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20
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21
Scheduling policies/algorithms
  • Static/Dynamic algorithms
  • Centralized/Distributed
  • Policies
  • FCFS
  • LCFS
  • Priority
  • Round-Robin
  • Weighted Fair Queuing

22
Service policies for the server with vacation
model
  • Exhaustive
  • Gated
  • Semi-gated
  • K-limitted

23
Scheduling on a grid
  • Resources under the control of different
    administrative authorities.
  • Resource reservations.
  • Market-based scheduling algorithms.

24
Scheduling on a grid
25
Security models
  • Problems and solutions
  • Confidentiality ? encription
  • Authentication ? authentication services
  • Authorization (controlled access to system
    resources) ? access control

26
Secret key and public key cryptography
27
Major challenges in distributed systems
  • Concurrency
  • Mobility

28
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