26prajval98 / fq-pie-ns-3

Implementation of the FQ-PIE algorithm in ns-3

FQ-PIE-ns-3

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Resources used:

1. RFC 8033, Proportional Integral Controller Enhanced (PIE) https://tools.ietf.org/html/rfc8033

2. RFC 8290, Fq-Codel https://tools.ietf.org/html/rfc8290

3. NS3 documentation (Doxygen), https://www.nsnam.org/doxygen/

4. Algorithm for PIE followed, https://tools.ietf.org/html/rfc8033#appendix-A

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Implementation Details (details)

Implementation of FQ-PIE was done in NS3

Files

• fq-pie-queue-disc.h (Click here)
  This file contains the basic definition of the the FqPieFlow class and FqPieQueueDisc class.

• fq-pie-queue-disc.cc (Click here)
  This file contains all the declarations of the functions in fq-pie-queue-disc.h

• fq-pie-example-tcp.cc (Click here)
  This file creates an environment where only TCP packets are in the network

• fq-pie-example-udp.cc (Click here)
  This file creates an environment where only TCP and UDP packets are in the network

Algorithm (important functions)

• doEnqueue :
  Whenever a packet comes into the node (maybe a router), this function is called.
  For each flow of packet a hash function is used to determine where the packet which flow (or slot) the packet will be added to, There might be hash collisions possible.
  If the hash value h is not present in the list of flows, a new flow is created with a new queue disc qd, else the flow which is already present is selected.
  If flow status is INACTIVE then the flow status is set to NEW_FLOW and a quantum deficit is added
  Then pie algorithm is applied as mentioned in the Resources.
• doDequeue :
  Here the DRR algorithm is used in order to determine which queue has to dequeue. While checking for flows to dequeue, new flows are checked first. A flow is rendered old right after its checked for a packet to DQ. If there are no appropriate packets in new flow, an old flow is considered.
• calculatePFlow :
  Simulator::Schedule is used to schedule this function every mt_Update unit of time. It calls another function calculateP which performs the PIE variant of calculation of probability except that this is done to every flow ACTIVE.

Important variables

• Pie variables for each flow :
  bool m_inMeasurement ( Indicates whether we are in a measurement cycle )
  double m_avgDqRate ( Time averaged dequeue rate )
  double m_dqStart ( Start timestamp of current measurement cycle )
  uint64_t m_dqCount ( Number of bytes departed since current measurement cycle starts )
  double m_dropProb ( Variable used in calculation of drop probability )
  uint32_t m_burstReset ( Used to reset value of burst allowance )
  Time m_qDelayOld ( Old value of queue delay )
  Time m_qDelay ( Current value of queue delay )
  BurstStateT m_burstState ( Used to determine the current state of burst )
  Time m_burstAllowance ( Current max burst value in seconds that is allowed before random drops kick in )
  

• Fq-PIE variables :
  Time m_sUpdate ( Start time of the update timer ) Time m_tUpdate ( Time period after which CalculateP () is called ) Time m_qDelayRef ( Desired queue delay ) uint32_t m_meanPktSize ( Average packet size in bytes ) Time m_maxBurst ( Maximum burst allowed before random early dropping kicks in ) double m_a ( Parameter to pie controller ) double m_b ( Parameter to pie controller ) uint32_t m_dqThreshold ( Minimum queue size in bytes before dequeue rate is measured ) uint32_t m_quantum ( Deficit assigned to flows at each round ) uint32_t m_flows ( Number of flow queues ) uint32_t m_perturbation ( hash perturbation value )

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Weekly Progress (details)

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Result and Analysis (details)

PIE vs FQ-PIE

1. Only when TCP packets are present in the Network :

Drops	PIE	FQ-PIE
Random Drops	204	0
Queue limit Drops	0	0

2. When both TCP and UDP packets are present in the Network:

Drops	PIE	FQ-PIE
Random Drops	3512	483
Queue limit Drops	454	0

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Conclusion

• Fq-PIE is a drastic increment over the already existing problem and handles the buffer bloat problem really well.
• As comparision of Fq-PIE with other AQMs is not done it is currently not possible to compare its performance with others.
• These results are only representative of how better FqPie is with respect to Pie.

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Further

• Comparison with FqCodel and Codel is yet to be done as a test-suite could not be prepared.
• CAKE implementation and comparison with FqPIE
• Only Basic FQ-PIE has been implemented. A enhanced version can be used for better results. Enhanced PIE

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