the computer communication lab 236340 spring 2008
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The Computer Communication Lab (236340) Spring 2008. Color Aware Switch algorithm implementation. Agenda. Introduction Project scope Dune’s color-aware algorithm DiffServ Project Implementation Test results Open discussion. Introduction. Switches with multiple flows.

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the computer communication lab 236340 spring 2008

The Computer Communication Lab (236340)Spring 2008

Color Aware Switch algorithm implementation

agenda
Agenda
  • Introduction
  • Project scope
  • Dune’s color-aware algorithm
  • DiffServ
  • Project Implementation
  • Test results
  • Open discussion
introduction
Introduction
  • Switches with multiple flows.
    • Packets arrive at several ports are colored (GREEN and YELLOW)
    • Congestion on some of the ports.
    • Packets are dropped.
  • Requirements:
    • Yellow packets are dropped before green.
    • No bandwidth loss.
project scope
Project Scope
  • Implement Dune’s algorithm for color-aware switch (specification is provided)
  • Provide an experimental platform (based on NS-2) for further exploration
color aware algorithm
Class Q

Central

FSM

*

Max

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Q

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Size

Agent

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Flow

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ID

(

per input

)

e

u

*

Aging

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Time

e

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Max

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Q

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Size

Q

t

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p

n

I

Input

1

Credit Message

Class Q

Max

-

Q

-

Size

e

u

e

u

.

Q

t

.

u

p

.

n

I

Input

2

Output port

.

.

.

Class Q

Max

-

Q

-

Size

e

u

e

u

Q

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Input N

Color Aware Algorithm
color aware algorithm 2
Color Aware Algorithm 2
  • Each input has access to Test Parameters Table for each color.
  • Each input holds Max-Q-Size for all inputs that are mapped to the same output.
  • Central Agent maintains Max-Q-Size by receiving “Flow Status Messages” from various inputs.
  • When a packet is evaluated for enque, a RED-like test vs. Max-Q-Size is performed. The packet is dropped or accepted depending on Test Parameters.
  • Central Agent updates the Max-Q-Size on each non-empty input using Round Robin every given time.
differentiated services
Differentiated Services
  • DiffServ is mechanism for classifying and managing network traffic.
  • DiffServ architecture has 3 components:
    • Policy
      • In NS, the policy is fully determined in the tcl script
    • Edge routers
      • Assign code points to the packets according to the policy
    • Core routers
      • Evaluate packets according to priority given on Edge
differentiated services 2
Differentiated Services - 2
  • In NS, each link has number of physical and virtual queues that represent priorities.
  • Queues are implemented on node’s egress. Therefore, when congestion occurs, packets are dropped on egress.
project s implementation
Project’s Implementation
  • DiffServ is used to mark packets depending on source-destination pair.
  • Each packet is then evaluated for dropping by its input before standard NS dropping algorithms.
  • Several topologies are built to test implementation.
  • Tests were run and results analyzed.
implementation details
Implementation details
  • Since queues are implemented on the egress, we’ve created physical queue for each input link.
  • CA manages physical queues only to determine which packets should be dropped.
  • CA notifies each non-empty physical queue about the maximum size of all other queues.
  • Custom statistics were made for the algorithm.
topology
Topology

Each source sends packets with constant bitrate.

Each link to edge contains both yellow and green packets

Congestion is created on Edge’s output.

S1

2Mb

A

5Mb

S2

10Mb

E

D

S3

5Mb

Packets are evaluated vs. CFG-Table and (if not dropped) by standard NS algorithms.

Various settings were tested to find optimal values.

B

S4

2Mb

testing various parameters
Testing various parameters
  • The tests were run with changing the following parameters for both colors:
    • CFG-AdmitDropProb1
    • CFG-AdmitDropProb2
    • CFG-AdmitTh
    • CFG-AdmitDropTh
    • CFG-DropTh
    • Port delay
drops vs tresholds
Drops vs. tresholds

CFG-AdmitDropProb1=30%

CFG-AdmitDropProb2=40%

CFG-AdmitDropProb1=40%

CFG-AdmitDropProb2=50%

CFG-AdmitDropProb1=20%

CFG-AdmitDropProb2=50%

CFG-AdmitDropProb1=60%

CFG-AdmitDropProb2=80%

Thresholds:

tests vs weighted red single q
Tests vs. Weighted RED Single Q

Dune’s algorithm

Approximated weighted RED (one queue)

Thresholds and probabilities:

CFG-AdmitDropProb1=10%

CFG-AdmitDropProb2=35%

CFG-AdmitDropProb1=20%

CFG-AdmitDropProb2=50%

tests vs weighted red double queue
Tests vs. Weighted RED Double Queue

Dune’s algorithm

Approximated weighted RED (double queue)

CFG-AdmitDropProb1=10%

CFG-AdmitDropProb2=35%

CFG-AdmitDropProb1=20%

CFG-AdmitDropProb2=50%

Thresholds:

drops vs port delay
Drops vs. port delay
  • CFG-AdmitTh = 30
  • CFG-AdmitDropTh = 60
  • CFG-DropTh = 70
  • CFG-AdmitDropProb1 = 50%
  • CFG-AdmitDropProb2=70%
  • Test parameters:
    • CFG-AdmitTh = 50
    • CFG-AdmitDropTh = 60
    • CFG-DropTh = 90
    • CFG-AdmitDropProb1 = 20%
    • CFG-AdmitDropProb2=50%
topology 2
A

10Mb

10Mb

E

D

10Mb

B

Topology (2)

Dune

Dune

Linear

WREDDoubleQueue

WREDSingleQueue

  • Test parameters:
    • CFG-AdmitTh = 20
    • CFG-AdmitDropTh = 40
    • CFG-DropTh = 80
    • CFG-AdmitDropProb1 = 10%
    • CFG-AdmitDropProb2=35%
  • CFG-AdmitTh = 10
  • CFG-AdmitDropTh = 30
  • CFG-DropTh = 50
  • CFG-AdmitDropProb1 = 20%
  • CFG-AdmitDropProb2=50%
topology 3
Topology (3)

A

3Mb

10Mb

E

D

9Mb

B

Dune

Dune

Linear

WREDDoubleQueue

WREDSingleQueue

  • Test parameters:
    • CFG-AdmitTh = 20
    • CFG-AdmitDropTh = 40
    • CFG-DropTh = 80
    • CFG-AdmitDropProb1 = 10%
    • CFG-AdmitDropProb2=35%
  • CFG-AdmitTh = 10
  • CFG-AdmitDropTh = 30
  • CFG-DropTh = 50
  • CFG-AdmitDropProb1 = 20%
  • CFG-AdmitDropProb2=50%
conclusions
Conclusions:
  • Large difference in dropping probabilities gives better results (more priority to green packets).
  • Global Max-Q-Size has its equilibrium. In CBR traffic thresholds distance has minor effect.
  • Port delay (Max-Q-Size update period) doesn’t have much impact on results for cbr traffic, unless its value is unreasonable.
  • Linearization of Dune algorithm at some topologies gives improvement to efficiency.
  • In general, Dune’s algorithms gives better results than WRED, however there are counterexamples.
slide20
Demo
  • Implementation modules
  • Tests and Topologies
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