Package io.aeron.driver

Class OptimalMulticastDelayGenerator

java.lang.Object
io.aeron.driver.OptimalMulticastDelayGenerator
All Implemented Interfaces:
FeedbackDelayGenerator
public class OptimalMulticastDelayGenerator extends Object implements FeedbackDelayGenerator
Feedback delay used for NAKs as well as for some retransmission use cases.

Generates delay based on Optimal Multicast Feedback
http://tools.ietf.org/html/rfc5401#page-13

maxBackoffT is max interval for delay

C version of the code: 


 double RandomBackoff(double maxBackoffT, double groupSize)
 {
     double lambda = log(groupSize) + 1;
     double x = UniformRand(lambda / maxBackoffT) + lambda / (maxBackoffT * (exp(lambda) - 1));
     return ((maxBackoffT / lambda) * log(x * (exp(lambda) - 1) * (maxBackoffT / lambda)));
 }
where UniformRand(x) is uniform distribution from 0..max

In this implementation's calculation:

  • the groupSize is a constant (could be configurable as system property)
  • maxBackoffT is a constant (could be configurable as system property)
  • GRTT is a constant (could be configurable as a system property)

N (the expected number of feedback messages per RTT) is:
N = exp(1.2 * L / (2 * maxBackoffT / GRTT))

Assumptions:

maxBackoffT = K * GRTT (K >= 1)

Recommended K:

  • K = 4 for situations where responses come from multiple places (i.e. for NAKs, multiple retransmitters)
  • K = 6 for situations where responses come from single places (i.e. for NAKs, source only retransmit)

  • Constructor Details

    • OptimalMulticastDelayGenerator

      public OptimalMulticastDelayGenerator(double maxBackoffT, double groupSize)
      Create new feedback delay generator based on estimates. Pre-calculating some parameters upfront.
      Parameters:
      maxBackoffT - of the delay interval
      groupSize - estimate

  • Method Details

    • generateDelayNs

      public long generateDelayNs()
      Generate a new delay value on initial request.
      Specified by:
      generateDelayNs in interface FeedbackDelayGenerator
      Returns:
      delay value in nanoseconds

    • shouldFeedbackImmediately

      public boolean shouldFeedbackImmediately()

    • generateNewOptimalDelay

      public double generateNewOptimalDelay()
      Generate a new randomized delay value in the units of maxBackoffT}.
      Returns:
      delay in units of maxBackoffT.

    • uniformRandom

      public static double uniformRandom(double max)
      Return uniform random value in the range 0 to max.
      Parameters:
      max - of the random range
      Returns:
      random value

    • toString

      public String toString()
      Overrides:
      toString in class Object