Adapt Tutorial
40 pages
English

Adapt Tutorial

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40 pages
English
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Description

Adaptive(Group Communication) ProtocolsRobbert van RenesseCornell University‹ÅÆWhy Adaptivity?Need to respond to changes in:– Network load– Connectivity (e.g., connected mobile)– Resource availability – Application traffic patterns– Security concerns (e.g., intrusions)Programming AdaptivityASSUMPTIONS VIOLATIONSCONFIGURATIONANALYSISRESOURCE PERFORMANCERESERVATION MONITORINGDynamic ConfigurationInitial NewFinalizeconfiguration configurationViolation of ReconfigureAssumptions (adaptation)Example -- FirewallNew GroupwareFirewallparticipantSignCryptApproaches1) write complex code to adapt to manysituations.2) write many pieces of simple code, eachdealing with a small problem in a particular situation, and configure and reconfigure on-the-fly.Æ‹‹‹Problems with first approachComplex protocolsHard to tune, optimize, prove correctWhen multiple such protocols are composed into a protocol stack, they fight with one another oscillation‹‹‹‹Problems with second approachGetting the interfaces right is difficultMay lead to performance problemsReconfiguration on-the-fly is difficultCorrectness concerns while switching‹‹Example: total orderSpec: if two processes P1 and P2 both deliver messages M1 and M2, they do so in the same order– even if they were sent by different processesUseful for replication: all replicas need to receive updates in the same orderNo protocol…Protocol 1: sequencerSEQSequence number ...

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Nombre de lectures 20
Langue English

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Adaptive (Group Communication) Protocols
Robbert van Renesse
Cornell University
Why Adaptivity?
‹
Need to respond to changes in:
– Network load
– Connectivity (e.g., connectedÅÆmobile)
– Resource availability
– Application traffic patterns
– Security concerns (e.g., intrusions)
ProgrammingAdaptivity
ASSUMPTIONS
CONFIGURATION
RESOURCE RESERVATION
VIOLATIONS
ANALYSIS
PERFORMANCE MONITORING
Dynamic Configuration
Initial configuration
Violation of Assumptions
Finalize
Reconfigure (adaptation)
New configuration
Example --
Firewall
Firewall
New Groupware participant
participant
Sign
Crypt
Approaches
1) write complex code to adapt to many
situations.
2) write many pieces of simple code, each
dealing with a small problem in a
particular situation, and configure and
reconfigure on-the-fly.
Problems with first approach
‹
Complex protocols
‹Hard to tune, optimize, prove correct
‹When multiple such protocols are composed into a protocol stack, they fight with one anotherÆoscillation
Problems with second approach
‹
Getting the interfaces right is difficult
‹May lead to performance problems
‹Reconfiguration on-the-fly is difficult
‹Correctness concerns while switching
Example: total order
‹Spec:if two processes P1 and P2 both deliver messages M1 and M2, they do so in the same order –even if they were sent by different processes
‹Useful for replication: all replicas need to receive updates in the same order
No protocol…
Protocol 1:sequencer
SEQ
Sequence number centralized in sequencer
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