Dynamic-CBT

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Dynamic-CBT

• Better Performing Active Queue Management for
  Multimedia Networking

Jae Chung and Mark Claypool
Computer Science Department Worcester Polytechnic
Institute Worcester, Massachusetts, USA
http//perform.wpi.edu/
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Outline

• Introduction
• CBT
• D-CBT
• Evaluation
• Issues

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Internet Routers Today

• Volume of traffic increasing
• More simultaneous active flows
• Increase in multimedia flows
• Tight timing constraints
• Different flow-control mechanism than TCP
• Emphasis on Congestion Control and Fairness among
  active flows

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Current Router Queue Mgmt
Drop Tail (FIFO)
Resource Reservation
Active Queue Mgmt
...
FRED
...
CBQ
RED
(Lin, Morris 97)
( Floyd, Jacobson 95)
( Floyd, Jacobson 93)
Class-Based Threshold (CBT)
(Parris, Jeffay, Smith 99)
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CBT Design
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CBT - Pros and Cons

• Pros RED Class-Based Isolation
• Early congestion notification
• Protect TCP and protect Tagged UDP (MM)
• Different classes of flows coexist with
  predefined fairness
• Cons CBQ function w/o admission control
• Fairness for changing traffic mixes
• Utilization on outgoing link
• Changes Best-Effort nature of Internet

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Dynamic-CBT (D-CBT)
Drop Tail (FIFO)
Resource Reservation
Active Queue Mgmt
...
CBQ
RED
FRED
...
Class-Based Threshold (CBT)
Dynamic-CBT
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D-CBT Design
RED
Tagged UDP (MM)
Early Drop Test
Queue Manager
Untagged UDP
Classify
TCP
Threshold Test is activated when red_avg gt
red_min
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Evaluation using NS

• Developed a flow-controlled Multimedia
  Application (for tagged UDP class)
• AIMD Media Scaling (5 discrete rates)
• MPEG-1 like transmission rates
• Implemented and validated CBT
• Implemented D-CBT and measured congestion time
  fairness
• RED vs. CBT vs. D-CBT

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Simulation (RED, CBT, D-CBT)
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Fairness RED
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Fairness CBT
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Fairness D-CBT
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D-CBT Issues

• Tagging UDP packets
• Who tags packets? (End Host? ISP?)
• Which field of IP header to use?
• IPv4 Unused Bit in Type-Of-Service Field
• IPv4 Another Protocol in Protocol Field
• IPv6 Use Priority Field
• Define a flow
• IPv4 Source-Destination Address
• IPv6 Plus Flow-ID

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D-CBT Issues

• Active Flow Counting (Overhead)
• For every incoming packet, insert or update
  ltdest-addr, flow-id, local-timegt info and update
  count
• Hash Table - O(1)
• Every ? ms, delete old flows and update count
• Hash Table - O(n)
• Measure Active Flow Counting overheads
• Linux implementation
• Processing Time and Memory Usage

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D-CBT Issues

• Test D-CBT with other (available) flow-controlled
  MM Applications
• Effect of the thresholds on MM quality
• Sensitivity of D-CBT to RED parameters
• How many different classes are needed?
• Example
• 1 class is RED
• 1 class per flow is FRED
• Overhead per class