Adaptive Queue Management Algorithm

1
Adaptive Queue Management Algorithm

• Red vs. Blue
• Presented by Hui Dong Lingyan
  Zhang
• Ying B. Wang

2
Outline

• Problems and Motivation
• Congestion control and active queue management
  currently used today (RED)
• BLUE algorithm
• Performance comparison

3
Problems Motivation

• High packet loss rates in
• Tcp/Ip network traffic
• Goal
• Queue management algorithms for maximizing
  network efficiency in times of heavy congestion
• 0 packet loss, 100 link utilization, low
  queuing delay

4
Red (Random Early Detection) Queue Management
Algorithm

• Exponentially weighted moving average
• of queue length
• Min th lt L average queue lt Max th
• Packets are randomly dropped or marked
• L average queue gt Max th
• All packets are dropped or marked
• L Queue length.

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Red Queue Management Algorithm
1
Pdrop
maxp
0
minth
maxth
Qave
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RED example 7 time steps
L Mbs
Sources
Receivers
A
B
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Disadvantage of RED

• Does not adapt well to traffic
• Reason
• Rely on queue length as an estimator of
  congestion
• Queue length grow shrink rapidly upon severity
  of congestion

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Blue Queue Management Algorithm

• Class of fundamentally different queue management
  algorithms
• Decouple congestion management from queue length
• Based on packet loss and link utilization history

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Blue algorithm

• Single dropping/marking probabilityPm
• Increment upon packet loss increases
• Decrease when link underutilized
• Freeze value upon changing

Upon packet loss if ((now - last_update) gt
freeze_time) then Pm Pm ? 1 last_update
now Upon link idle if ((now - last_update) gt
freeze_time) then Pm Pm - ? 2 last_update
now
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Ideal Scenario (Blue Algorithm)
L Mbs
Sources
Receivers
A
B
Rate L Mbs
Receiver generate DupACKs/ECN
Queue drops and/or ECN marks at steady rate Rate
Exactly what will keep sending rate at L Mbs
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Performance comparison

• Packet loss rates of Red and Blue over different
  queue size (1000 Tcp sources)

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Performance comparison

• Packet loss rates of Red and Blue over different
  queue size (4000 Tcp sources)

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Performance comparison

• Link utilization of Red and Blue

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Advantage of Blue

• Congestion control with minimal buffer
• Reduce end-to-end delay
• More memory for larger routing table
• Allow legacy routers to perform well even with
  limited memory

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Little Concerns about Blue

• Parameters setting
• -- freeze_time (Based on round-trip times of
  connections over the link)
• It determines the minimum time interval
  between two successive updates of Pm.
• Fast Ethernet, ATM, What about wireless or
  satellite link? Or heterogeneous network?
• Can a Router be so Smart?

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Resources Link
For more details, please go to IEEE/ACM
Transactions on Networking (TON) Volume 10 , 
Issue 4  (August 2002) Or http//www.thefe
ngs.com/wuchang/work/blue/
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Comment question
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