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									                                  Active Queue Management in Internet and Wireless Networks
                                                                                                             X. Deng, S. Yi, G. Kesidis and C. R. Das
                                                                                                                The Pennsylvania State University

ABSTRACT                                                                                                                              METHOD (CONT)
  In this research, we use a control theoretic approach to develop a generic                                                          Use Rate-based AQM for Uplink Traffic in Wireless LANs
framework for analyzing various active queue management (AQM)                                                                         • Ensure fairness for downlink/uplink traffic
schemes as proportionally-integral-derivative (PID) controllers. Based on                                                             • Can work together with downlink queue-based AQM for Queue
this PID model, we propose an adaptive control mechanism to improve                                                                   management and QoS provisioning
the system stability and performance under changing network conditions.                                                                         AQM(Gc)   p      TCP (Gt)  Queue (Gq)     q
A simulation study under a wide range of traffic conditions suggests that
the proposed algorithms outperform the existing AQM schemes in
achieving better system performance and stability. We then apply the                                                                                                -1
AQM concept to achieve fairness bandwidth allocation between downlink
and uplink traffic in wireless LANs                                                                                                                                      TCP (Gt)                   

MOTIVATION                                                                                                                                                   p                                   Uplink
                                                                                                                                                                   AQM(Gc)          -1
Modeling TCP/AQM
• A control-theoretic model for TCP and RED [Hollot’01].
• Extend this model to incorporate more end-system and AQM controller
  • Proportional-Integral-Derivative (PID) controller – A unified                                                                     RESULTS
  framework for design and analysis of AQM schemes.
  • System stability is related to network and traffic condition – use                                                                 • Putting everything together :          GC  K P 
                                                                                                                                                                                                 KDs

  Adaptive Control for a better stabilized and robust system

AQM for Wireless Networks
• More variable in bandwidth and delay
• Uplink/Downlink asymmetry

                     W                                        q
                                                                           AQM                                   Queue
     TCP                      N                     queue
   dynamic                                         dynamic
                              R                                                                           FIFO

                                                                                                                                       • Stabilized queue size with varying traffic loads and link delays
                                                                                                                                        • Reduced packet loss and response time
             time delay
               R secs


                                                                          AQM(Gc)         p    TCP (Gt)  Queue (Gq)       q

                                                                        Controller                 Plant (Gp)
                                                                  Linearized TCP/AQM System                              rate based
                                                                   •N: Number of connections
                                                                   •W: TCP congestion window
                                                                   •R: Round trip time
                                                                   •: Packet arrival rate
                                                                   •q: router queue size
                                                                   •p: packet drop/mark probability
                                                                                                                                       • Better Fairness between uplink/downlink traffic by using PI control
METHOD                                                                                                                                 over packet arrival rate (AVQ) for uplink traffic in Wireless LAN
• A Unified Framework for Design and Analysis of AQM                                                                                                                                               With AVQ
                                                                                                                                                    No AQM
• Interpreting and Calibrating AQM parameters as PID controlling
components to the TCP plant module.
• New Controlling Components in AQM
•     Derivative Control (D control): Use change of packet arrival rate
over time as the congestion indicator, in addition to the instantaneous
packet arrival rate (P control) and router queue length (I control).
•     Adaptive Control: The controlling parameters adaptively changes
with the steady state packet marking probability p0 using update
functions m and l, which increase monotonically (APID).
                                   q                        m( p)         l ( p0 )      p
                                                   Gc                                                                                 CONCLUSIONS
                                                        Gc  l ( p0 )  Gc

•   Virtual Queue Control: A New Combination of rate-based and                                                                          • Various AQM Schemes can be classified as different types of PID
queue-based control (QRVQ)                                     1  p0
                                                   p -                                  q                                           • Addition of derivative and adaptive control improves the stability of
                                                                  Gt                 Gq
                                              Cs                                                                                        the system under varying plant configurations.
                                                                                                                                        • A rate based AQM for uplink traffic in Wireless LANs enhances the
                                                                   -1                                                                   fairness and improves the QoS for downlink traffic.

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