Case Studies for Robust Self-Organizing Systems

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Individual Systems

  • Starfish, human body
  • Cope with lost/damaged parts
  • Regrow/relearn capabilities (self-healing) for survivability
  • Adaptable
    • It's not clear if self-organization occurs with external excitement (disturbance) or just centralized control; e.g., if the healing/adaptation happens because the genes are coded that way or they evolve and adapt.

Collective Systems

  • Wealth distribution (pareto), file sharing
  • Cope with environmental conditions, resource value, government interventions, wars, closed platforms, law suits
  • Regroup, redistribute, reopen
  • Adaptable
  • Self-organization with external disturbance, but no centralized control.

Engineered Systems

  • Routing, TCP behavior
  • Cope with environmental conditions, disasters, unknowns
  • Regroup, reroute, retransmit
  • Adaptable
  • Self-organization with external disturbance, but no centralized control.

Parliament

  • Well-defined structure and function
    • Mandate distribution is defined by distributions of citizens' votes
    • Goal is to make joint decisions in the interest of the citizens (or own electors) by voting

The parliament is (up to a certain minimum size) robust against instant and repeating (spreading)

  • failures/removals of nodes (i.e., representatives at the voting procedure)
  • faulty/unexpected/unwanted behavior of nodes, (e.g., personal decisions made under lack of information)
  • malicious behavior of nodes (corruption; voting against clear interest of citizens, but in pure interests of a person/small group/party; not disclosing decision-important information)

It shows the following properties:

  • Self-healing due to iterated renewals based on elections
  • External observation from mass media
  • Each representative may act as attractor, detractor, or neutral node
  • Adaptive to change in the social environment (e.g., role of women in the societies)
  • Shows the emergent property of issued laws initiated by some voters, set up by its representatives, and valid for all citizens
  • Reflects attributes of dependability: availability, reliability, safety, maintainability, and security

Robustness vs. Fault Tolerance

  • Fault Tolerance
    • Functionality is not harmed
    • Tolerance with respect to random failures
  • Robustness
    • includes fault tolerance
    • robustness against intended failure(malicous elements)
  • Systems cannot be robust against completly unknown events
    • Systems can only be robust with respect to known/defined perturbations
    • Definition of robustness has to include assumptions

Human Body

  • Immune system of human body
    • Adapts to new bacteria/viruses
  • Body recovers from little accidents
    • Decentralized reproduction of cells

Wikipedia

  • Self-organizing pool of information
  • Fault Tolerance against faulty information
    • Users correct random errors
  • Robust against malicous information to a certain degree
    • Vulnerable to distributed attacks (large number of users), e.g. members of political party insert malicous information about opponent

Fireflies

  • Popular example from biology
  • Blink together to achieve synchronization
  • For adaption a single firefly observes blinking of neighbors (local information)
  • Robust against failures of individual fireflies
    • Assumption: Network stays in connected state

Ant Nest

  • Goal
    • dependably find food and bring it back to the nest
  • Mechanism
    • randomly explore the surroundings
    • leave trails from foodsources back to the nest (via pheromones)
    • follow the pheromone trail with the highest pheromone concentration -
    • but allow for deviations from that path with a certain probability
  • Robustness
    • against dynamic food location changes (food churn)
    • against obstacles appearing on the path
    • against ants disappearing
  • Problems
    • degradation of robustness if high concentration of artificial pheromones are deposited

P2P Networks (Example: File Sharing)

  • Goal
    • provide data items to participating peers
  • Mechanism
    • distributed storage of data items on the peer nodes
    • distributed reference infos on the peer nodes (normally via DHT)
  • Robustness
    • against leaving/failing and joining peer nodes (node churn)
    • against bottlenecks in underlying IP network
  • Problems
    • attacks
    • manipulations
    • malicious nodes

Self-organizing traffic lights

  • Waiting time depends on number of cars waiting (only sensor being a single camera)
  • No explicit communication between the lights - communication media = cars
  • Emergence of grups of cars that propagate on a green wave
  • Robust to changes in traffic situation, break-down of single lights (if they fall into a fail-safe state, such as a flashing yellow light or shutting down completely).
  • Discussion: Depends a lot on the density of the traffic (jamming situations). Explicit communication for traffic may be desirable, even though that may go against the self-organizing nature of the system.

Self-organizing network routing

  • Any routing protocol broadcasting to discover a specific route (example: choose route which contains the packet with the highest TTL)
  • Ant routing
  • Robustness: break-down of nodes/lines, overload in parts of the network are handled in a self-organized way.
  • Limits: Package loss (needs to be handled by the upper layers)

Viruses and worms (whether this is truly a self-organizing network was left open for discussion)

  • Worms start out as sngle "agent" that broadcasts itself throughout the network
  • Infected network-node is closed and can't be infected again.
  • Is this "epidemic" distribution a kind of self-organization?
    • Multiple agents
    • Distribution
  • But:
    • Emergence of structure?
    • Adaptability to changes from the environment?