1. Distributed Systems Brief Overview CNT 5517-5564 Mobile & Pervasive Computing Dr. Sumi Helal University of Florida

2. Distributed System Values Reliability Availability Dependability Security Performance: response time, throughput, etc Scalability: vertical (concurrency) and horizontal (distribution) Fault-tolerance

3. Distributed System Values, cont’d Consistency Up-to-date-ness Adaptability Reconfigure-ability Manageability Extensibility more

4. Reliability Eternal: Mean Time to Failure (MTTF) Extended Reliability = Availability – (1) Employing Redundancy (replication) – (2) Employing specific Recovery Procedures – In either (1) or (2): First detect failure Second Mask it (redundancy), or Recover from it (recovery)

5. Availability Past: Today: – As past, plus: – Available through a variety of networks – Available through a variety of devices – Available through a variety of locations (e.g., while mobile? ) 4 nine’s = 0.9999

6. Replication in Distributed Systems Consider data, how can we use replication of data to increase its availability and use?

7. Replication Management Protocols

8. Distributed Systems Intricacies Synchronization: multiple clocks (difficult to agree on exact time) Concurrency: multiple simultaneous accesses potentially conflicting. Failures: high probability of failures (too many components). Complex failure modes (single, multiple simultaneous, network partition, …) Consensus: difficult to reach consensus (odds includes failures, lack of synchronization, …) more …

9. Distributed Computing Models Client/Server Approach Multi-tier Approach Peer-to-Peer Approach Agent based systems Mobile Code (Applets, mobile agents,..) Service-oriented computing – Service registration/discovery – Service composition Cloud Computing

10. The Emerging Computing Model: Cloud, Edge & Beneath Cheaper to provide services to a thin client than to maintain a fat client in a changing world (service Science) Besides the Cloud, all other computing infrastructures become simply Edge Devices to the Cloud Do Sensors count in this new world of Clouds? Are Sensors Edge Devices?

11. Cloud, Edge & Beneath Sensors – to - Cloud

12. Cloud, Edge & Beneath Gateway – to Cloud

13. Cloud, Edge & Beneath Sensors – to – Edge; Edge – to- Cloud In Network Computing The Case for the Edge Cloud Computing