Adapt Tutorial

Amyfish

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 ...

Informations

• Publié par: Syas
• Nombre de lectures: 30
• Langue: English

Extrait

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