com.theorem.radserver3.radutil
Class Retransmission

Object
  Retransmission

public class Retransmission

extends Object

Client retransmission class.

The client should try to avoid congestion and synchronization problems by using this class to determine time outs to use when waiting for reply packets. Congestion failure occurs usually when a server is overwhelmed with requests from a large number of clients will use a short fixed timeout for retransmissions. This class will use progressively longer time outs until a maximum time out is reached. If more retries are required the Retransmission class will restart with the minimum time out.

To avoid synchronization problems that can occur when a number of clients start to synchronize their retransmissions some 'jitter' is added to the time out period so that the wait time is not measured in one second granularity.

Typically this class will be used to back off if a transmission fails and an exception is thrown. It will add extra time between retransmissions of a client packet.

This performance is based on four variables:

• The minimum time out (Initial time out value).
• The maximum time out (after which the minimum timeout will be used).
• The jitter which is given as the maximum whole percent (20 = 20%) used to vary the initial and calculated time outs. This is further varied by a random multipler.
• The count - the number of retries to perform.

Constructor Summary

Retransmission(int minimumTimeout, int maxTimeout, int jitter, int count)
Constructor.

Method Summary

void	cancel() Cancel this retransmission wait.
long	getTimeout() Calculate the new time out based on the last time out.
static void	main(String[] a)
boolean	pause() Pause between each retry.
void	reset() Reset the time out calculations for a fresh time out.

Methods inherited from class Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Retransmission

public Retransmission(int minimumTimeout,
                      int maxTimeout,
                      int jitter,
                      int count)

Constructor.

Parameters:

minimumTimeout - On a retransmission this would be the minimum time out. For example it could be 5 seconds.

maxTimeout - This is the maximum time out possible. For example it could be 60 seconds.

jitter - This is the 'inaccuracy' in the actual timeout measured in percent and is applied randomly within this range. It prevents clients from all synchronizing to some exact time out like once each second. With a jitter value of 20 the first time out might occur in .8 seconds or 1.2 seconds within the range of the time out.

count - The number of retries to make. This is the number of retries beyond the first attempt.

Method Detail

cancel

public final void cancel()

Cancel this retransmission wait. This can only be used by another thread. An interrupt on this thread will also cancel the pause().

getTimeout

public long getTimeout()

Calculate the new time out based on the last time out.

Returns:

Time out.

main

public static void main(String[] a)

pause

public final boolean pause()

Pause between each retry. This is broken by the retry count being reached or a thread interrupt.

Returns:

true if the count is reached, false otherwise.

reset

public void reset()

Reset the time out calculations for a fresh time out.