leonard kleinrock distinguished professor computer science department ucla

Leonard Kleinrock 2010

Leonard KleinrockLeonard KleinrockDistinguished ProfessorDistinguished Professor

Computer Science DepartmentComputer Science DepartmentUCLA UCLA


• Many youth feel there is no great work left to Many youth feel there is no great work left to be done.be done.

• Not true – the golden era continues.Not true – the golden era continues.• There are lots of challenging problems left.There are lots of challenging problems left.• And their impact will be great inAnd their impact will be great in

• today’s global economytoday’s global economy• and in tomorrow’s unimaginable and in tomorrow’s unimaginable world.world.

• These are times of enormous change.These are times of enormous change.• And times of enormous opportunity.And times of enormous opportunity.

Golden OpportunitiesGolden Opportunities


Don’t ForgetDon’t Forget• But as we rush headlong into the future, we must not forget where all this came from – we must not ignore the lessons from history.• Most of today’s youngsters cannot

remember a time when there was no Internet. • They cannot imagine that their parents are “of this era”• Don’t underestimate those seniors.


My Five Golden Guidelines to My Five Golden Guidelines to ResearchResearch

1.1. Conduct the 100-year test.Conduct the 100-year test.2.2. Don’t fall in love with your model. Don’t fall in love with your model. 3.3. Beware of mindless simulation.Beware of mindless simulation.4.4. Understand your own results.Understand your own results.5.5. Look for “Gee, that’s funny!”Look for “Gee, that’s funny!”


Richard HammingRichard Hamming"Why do so few scientists make significant contributions and so many are forgotten in the long run?"

Richard W. Hamming, “You and Your Research”, March 7, 1986.

“If you don't work on important problems, it's not likely that you'll do important work.”


1. The 100 Year Test1. The 100 Year Test

• Hamming once asked me, Hamming once asked me,

““What progress of today will be remembered What progress of today will be remembered 1000 years from now ?”1000 years from now ?”

Will your work be remembered 100 years Will your work be remembered 100 years from today?from today?


2. The Modeling Process2. The Modeling Process

TheThe RealReal

WorlWorl

dd

MathematicaMathematicall

Model ofModel ofThe Real The Real

WorldWorld

Solution to Solution to thethe

MathematicMathematicalal

ModelModel


MathematicaMathematicall

Model ofModel ofThe Real The Real

WorldWorld

Solution to Solution to thethe

MathematicMathematicalal

ModelModel

2. But Don’t Fall in Love With 2. But Don’t Fall in Love With Your ModelYour Model

Approximation

TheThe RealReal

WorlWorl

dd


Michael FaradayMichael Faraday

• "I could not imagine much progress by "I could not imagine much progress by reading only, without experimental facts and reading only, without experimental facts and trials … I was never able to make a fact my trials … I was never able to make a fact my own without seeing it. “ (Faraday: 1827)own without seeing it. “ (Faraday: 1827)

• Faraday performed in his brain the work of a Faraday performed in his brain the work of a great mathematician without using a single great mathematician without using a single mathematical formula” (Hermann von mathematical formula” (Hermann von Helmholtz : April 5, 1881 )Helmholtz : April 5, 1881 )


3. Beware of Mindless3. Beware of MindlessSimulationSimulation


Ask the Obvious QuestionsAsk the Obvious Questions

Slope

3. Beware of Mindless3. Beware of MindlessSimulationSimulation

Intercept

Breakpoint

Asymptote


4. Understand Your Own Results4. Understand Your Own Results

Leonard Kleinrock 2010 Network CloudNetwork Cloud

InputInput

Response TimeResponse Time

TTRESPONSE TIMERESPONSE TIME

0

CAPACITYCAPACITY

Loss

LOSSLOSS


Response Time vs Throughput

0Throughput

ResponseResponse TimeTime

( )

T( )

Do you wantDo you wantto operateto operate

here?here?Or here?Or here?

Now let’s ask a good question:


0Throughput


( )

T( ) P = T( )

1/P

*

Max Power Point

Kleinrock, L., "On Flow Control in Computer Networks", Conference Record, Proceedings of the International Conference on Communications, Vol. II, Toronto, Ontario, pp. 27.2.1 to 27.2.5, June 1978.

Let me define a new metric of performance:

POWER = Throughput

Response Time

The main result

Response Time vs Throughput4. Understand Your Own Results

dT( )/d = T( )/dT( )/d = T( )/

Power is max when


0Throughput


( )

T( ) P = T( )

1/P

*

Max Power Point


We need a new metric of performance:

POWER = Throughput

Response Time



0Throughput


( )

T( )

*

Max Power Point



For M/M/1For M/M/1this givesthis gives

max Power at max Power atNN** = 1 = 1

Let’s Dig Deeper on Understanding

Why ?Why ?


4. Understand Your Own ResultsUse Your IntuitionUse Your Intuition

TTTT= Min= Min

Eff = MaxEff = Max


4. Understand Your Own Results

Only 1 customerOnly 1 customerin the systemin the system

TT= Min= MinEff = MaxEff = Max

Use Your IntuitionUse Your Intuition

Insight:Just keep

the pipe full!

TT


• Our intuition says put Our intuition says put exactlyexactly one person one person in the queueing system in the queueing system • This was from “deterministic” reasoning.This was from “deterministic” reasoning.

• We can’t actually do that in generalWe can’t actually do that in general• BUT our earlier result said that we should BUT our earlier result said that we should

adjust the system to achieve an adjust the system to achieve an averageaverage of of one person in the queueing system, i.e., one person in the queueing system, i.e.,

4. Understand Your Own Results

At Max PowerAt Max PowerNN** = 1 = 1

for M/M/1for M/M/1


5. Gee, that’s funny!5. Gee, that’s funny!


M/M/1M/M/1

M/G/1M/G/1

N*=1N*=1

0

T( )

5. Gee, that’s funny!What can we say for

M/G/1 ?


More on ModelingMore on Modeling

•Moving the frontier is tough Moving the frontier is tough (we mislead our students)(we mislead our students)

•Once you do it, you will be able to repeat it Once you do it, you will be able to repeat it (students don’t believe us)(students don’t believe us)•Teach your students to understand their results!Teach your students to understand their results!•Generalization usually comes when you can Generalization usually comes when you can see the simplicity of a solutionsee the simplicity of a solution•Keep your interest in related areas - areas Keep your interest in related areas - areas where where

something might happen.something might happen.


Thank YouThank Youwww.lk.cs.ucla.edu

leonard kleinrock distinguished professor computer science department ucla

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