Monte Carlo simulation on when two networks or more networks fail together and for how many minutes (how robust does OOB network need to be, to have reasonable probability that both networks are not down at the same time)

netmonte.rb

#!/usr/bin/env ruby

module NetMonte

STANDARD_DEVIATION = 2.5
MINUTES = 365*24*60

class Simulate
  def initialize years, *networks
    years.times do |year|
      nets = init_networks networks
      roulette year, nets
    end
  end

  private

  def roulette year, nets
    MINUTES.times do |minute|
      nets.each do |net|
        net.run minute
      end
      if nets.all? { |net| net.down }
        puts "outage at year #{year}, minute #{minute}"
      end
    end
  end

  def init_networks networks
    nets = []
    networks.each do |net|
      outage_count  = RandomGaussian.new net[:outage_count],  STANDARD_DEVIATION
      outage_length = RandomGaussian.new net[:outage_length], STANDARD_DEVIATION
      nets << Network.new(outage_count.rand, outage_length)
    end
    nets
  end

end

class Network
  attr_reader :down
  def initialize outage_count, outage_length
    @down       = false
    @outage_end = 0
    @outage_probability = (1 / ((outage_count/365)/1440)).to_i
    @outage_length = outage_length
  end
  def run minute
    if @down and minute > @outage_end
      @down = false
    end
    if rand(@outage_probability) == 42
      @down = true
      @outage_end = minute + @outage_length.rand
    end
  end
end

#stole from SE
class RandomGaussian
  def initialize(mean = 0.0, sd = 1.0, rng = lambda { Kernel.rand })
    @mean, @sd, @rng = mean, sd, rng
    @compute_next_pair = false
  end

  def rand
    if (@compute_next_pair = !@compute_next_pair)
      # Compute a pair of random values with normal distribution.
      # See http://en.wikipedia.org/wiki/Box-Muller_transform
      theta = 2 * Math::PI * @rng.call
      scale = @sd * Math.sqrt(-2 * Math.log(1 - @rng.call))
      @g1 = @mean + scale * Math.sin(theta)
      @g0 = @mean + scale * Math.cos(theta)
    else
      @g1
    end
  end
end

end

begin
  if __FILE__ == $0
    netA = { outage_count: 3.0, outage_length: 180.0 }
    netO = { outage_count: 5.0, outage_length:  60.0 }
    NetMonte::Simulate.new 10000, netA, netO
    binding.pry
  end
end