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Nov 3, 2013 (3 years and 8 months ago)

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Distributed Systems

Brief Overview

CNT 5517
-
5564

Mobile & Pervasive Computing

Dr. Sumi Helal

University of Florida

Distributed System Values


Reliability


Availability


Dependability


Security


Performance: response time, throughput, etc


Scalability: vertical (concurrency) and
horizontal (distribution)




Fault
-
tolerance

Distributed System Values,
cont’d


Consistency


Up
-
to
-
date
-
ness


Adaptability


Reconfigure
-
ability


Manageability


Extensibility


more




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)


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

Replication in Distributed Systems


Consider data, how can we use replication of
data to increase its availability and use?

Replication Management Protocols

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





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


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?

Cloud, Edge & Beneath

Sensors


to
-

Cloud

Cloud, Edge & Beneath

Gateway


to Cloud

Cloud, Edge & Beneath

Sensors


to


Edge; Edge


to
-

Cloud

In Network

Computing

The Case for the Edge

Cloud Computing