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Research and Publications:A Personal Perspective

Bo Li

Hong Kong University of Science and Technology

Microsoft Research Asia

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Outline

What about research? How much does one have to learn? PhD research What is procedure of publications? How to write technical papers?

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Research is easy!

You have done this many times in course projects

Take a known problem, and apply a known technique

Obtain results, and write a report

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Research is difficult!

Is it technically correct? Does it make intuitively sense? Is it publishable, where and why? Does it offer some insights beyond

what we have known? Does it have any impact? …

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Research

There are basically four types of research works:

New problem and new solution New problem and old solution Old problem and new solution Old problem and old solution

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Research

Case I comes rarely, perhaps something you could only wish, once a life-time experience

Shannon theory Cases II and III are the ones that you

should target for Packet scheduling: weighted fair queuing Geographical routing in ad hoc networks

Case IV is where you can start Plenty of out there under the category of

“Yet another paper on … “

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Where do ideas come from?

Drink a beer, relax, ideas will come to you

The ideas fall from the sky!

Understanding the existing works, build upon that incrementally

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Where do ideas come from?

Ideas in most cases come from the deep understanding of a subject, and possess of broad knowledge

This is not a technical training, i.e., this is not about solving a bipartite graph, or differential equations

This is about relating them to real world problems This is about providing new insight beyond known This is about your creativity!

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Research: What is it?

Research = Re (repeat) + search Much of the research has been built upon

existing works, therefore a thorough understanding of those is the basis

Too many smart people in each area, so if an idea seems to be too good to be true, it likely is -> rethink that again

Each idea needs iterations: what is it? why has it not been done? what is the logical connection with the existing approaches?

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Research: Engineering Problem Each solution to an engineering problem is

only a trade-off; it is not a cure for all, it definitely has side-effect.

Networking coding Potential capacity gain under loaded system Is it really? Is there any alternative? What is the

penalty for doing so? Can we handle that in system design?

P2P Facilitate the voluntary file sharing Can this be extended beyond that?

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Case I: Adaptive Video Multicast

The need for multicast - efficiency

Multiple-unicast Multicast

Fundamental problem: users’ heterogeneity and network dynamics

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Case I: Adaptive Video Multicast

Layered video encoding and transmission Cumulative layered coding (Scalable coding)

Base layer: most important feature, low rate, low quality

Enhancement layers: progressively refine quality

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Case I: Adaptive Video Multicast

Existing solutions Multiple multicast tree, each for a layer Receiver adaptation: user’s joining and

leaving groups (receiver) Adaptation is performed at receivers only:

fixed layer rates and limited num of layers

Fundamental Problem The mismatch between the fixed sending

rate and the dynamic and heterogeneous rate requirement from receivers

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Case I: Adaptive Video Multicast

Layered Bit-stream

Bandwidth Report

Sender

A Recei ver

Layered VideoCoder

RateController

FeedbackCollector

LayeredRate

Calculator

LayeredDecoder

LayerAdapter

BandwidthEstimator

Multicast Network

Receiver 1

Receiver 2

Receiver N

Layered Bit-stream

......

BandwidthReport

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Case I: Adaptive Video Multicast

End-to-end adaptive video multicast Optimal rate allocation for each layer:

formulation and solution End-to-end transmission protocol and

whether TCP friendly Complexity analysis Practical issues: feedback explosion

(sampling), RTT estimation (open and closed loop)

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Sample References

B. Li and J. Liu, “Multi-Rate Video Multicast over the Internet: An Overview,” IEEE Network, (17)1: 24-29, January-February 2003.

J.-C. Liu, B. Li and Y.-Q. Zhang, “Adaptive Video Multicast Over the Internet,” IEEE Multimedia, (10)1: 22-33, January-March 2003.

J. Liu, B. Li, and Y.-Q. Zhang, “An End-to-End Adaptation Protocol for Layered Video Multicast Using Optimal Rate Allocation, IEEE Transactions on Multimedia, (6)7: 87-102, February 2004.

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Summary

Identify a general category of problems

The idea should be intuitively simple Publications can be “easier”

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Outline

What about research? How much does one have to learn? PhD research What is procedure of publications? How to write technical papers?

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How much does one have to learn?

I have learnt all the mathematics, and I am loaded Discrete algorithms, partial differential

equations, dynamic control, probabilistic modeling, information theory and etc.

I still don’t have a clue what to do in research.

Where in the world is research topic?

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How much does one have to learn?

I have read all papers out there from journals and conferences

Can I do research now? There is no way you can cope with all of

them Majority of the published works are junks,

and can cause brain damage and can be misleading

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The minimum needed for research

Logical thinking, after all we are in engineering world

Basic skills You have to know the Dijstra algorithm in order

to understand the OSFP (?) the ability to learn

Life long learning process, esp. in CS

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The minimum needed for research

Abstraction. Take a problem, you have to know What is/are the fundamental problem(s) You have to see both “forest and trees” What have been done, why? What are seemingly undoable?

Understand your strength and weakness

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The minimum needed for research

Open mind We are not dealing with math problem in that there

exists perfect solutions Engineering solutions are subject to argument and

debate, i.e., each solution is a trade-off, and it only works in a constrained environment

Critical mind When you read others, it is equally important to

understand what circumstance that it does not work as in which it works

If you can not identify such scenario, you are not understanding the problem

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Case II: Proxy Placement

How to place the proxy (mirror sites) in the internet

B. Li et al., “On the Optimal Placement of Web Proxies in the Internet,” Proc. IEEE Infocom'99

ACM Communications Review (2001) cited as the 1st ever work on this topic

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Case II: Proxy Placement

Formulation: graph theory problem, k-median problem: given N nodes, how to select K nodes to place the content so certain optimal criterion can be met

For general graph, this is NP-hard For tree, we solved this using a known dynamic

programming technique This turns out to be the fundamental problem

for object replication in DB, which has been cited over 300 times since then

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Sample References

J.-L. Xu, B. Li and D. Lee, “Placement Problems for Transparent Data Replication Proxy Services,” IEEE Journal Selected Areas in Communications, 20(7): 1383-1398, 2002

A. Vigneron, L. Gao, M. Golin, G. Italiano and B. Li, “An Algorithm for Finding a k-Median in a Directed Tree,” Information Processing Letter, 74(1-2): 81-88, 2000

B. Li, “Content Replication in a Distributed and Controlled Environment,” Journal of Parallel and Distributed Computing, 59(2), pp. 1-21, Nov. 1999

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Summary

Finding a problem is more important, and difficult than solving a problem

You need out-of-box thinking

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Outline

What about research? How much does one have to learn? PhD research What is procedure of publications? How to write technical papers?

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PhD Research

Make a plan earlier, for 3-4 years The research topics must be of current

interest, and state-of-the-art Don’t work on packet scheduling, and IEEE 802.11

MAC protocol Beating the performance of Ethernet is like kicking a

dead horse! It has to be something that within your

capability You need to understand your strength and

weakness, and be realistic (don’t shoot stars) You should know your interest, self-motivation is one

of the single most important factors

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PhD Research

Read top 10 or 20 papers in the area Understand the basics, fundamental

problems, and open issues Think and read

Put all papers into perspective Start from a small yet concrete problem

Build you skill and confidence Discussions generates ideas

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Reading

Top conference or workshop first ACM Sigcomm, ACM Mobicom, IEEE Infocom IEEE ICNP, IWQoS, MobiHoc

Second tier conference only for reference IEEE Globecom, ICC

Avoid bad conferences Regional, and less reputable ones

Read journal papers only it has not been published else where, or when it contains more detailed and complete treatment

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PhD Research

Focus! Don’t over-estimate your ability Don’t diversify too much

Start with small idea(s), publish in an easy conference in the 2nd year

Working plan: target at 2 conferences (20 or less acceptance rate) and one journal paper per year (in 2-3 years)

The thesis is a collection of the papers So you need to have a focus!

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Research Topics

Theoretical vs. practical Can this be related to a real world

problem Engineering approach

It should have a clear boundary Focus on what can or/and can not be done

Don’t lose the bigger picture Tree and the forest How does it help to solve one or more

pieces in the bigger problem

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PhD Research System works

System work usually involves team efforts Building from scratch is a dangerous thing The prototype has to demonstrate significance in

that either this is a proof of a concept, or demonstrate the feasibility

Less than 5% chance being useful, yet worth the investment for technical break through

Theoretical works Theoretical work usually provides an elegant solution

to a generalized problem The significance can be greatly enhanced if practical

insight can be drawn

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Advisor/Mentor

Choosing an advisor could be the single most important factor for your research Understanding the general problem, the ability to

identify the significance and yet another

Personal and professional relationship Junior vs. senior, hands-on or hands-off Regular guidance vs. direction Independent and close collaboration Group or individual effort Time, efforts and experience

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You really need an Advisor/Mentor

Can a rabbit eat a dog, fox and wolf?

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You really need an Advisor/Mentor

Punch line

It really does not matter what the topic is, and what you are doing, all it matters is

who your advisor is

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Example I: My PhD research What you need is a jump start for confidence building

A. Ganz and B. Li “Performance of Packet Networks in Satellite Clusters,” IEEE Journal on Selected Areas in Communications, (10)6: 1012-1019, August 1992

Be objective, don’t lose the bigger picture The research topics are both important and not so important The research works in PhD study is simply a training process,

be realistic. Usually the most productive period for one’s career is withi

n the 5 years’ after one’s PhD

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Example II: My student

Jiangchuan Liu Who has written close to 20 top journal papers since 1999, la

rgely on video multicast Assistant Professor at Simon Fraser Univ., former with Chine

se Univ. of Hong Kong. Won the prestigious Hong Kong Young Scientist award in 200

3, given to one individual annually by Hong Kong Institute of Science (HKIS)

Sometime direction is all a student needs

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Collaborations leads to Productivity

Working with the right people Skill complementary Same interests

Working with smart people

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Frequency Reuse Factor,

If total of S channels available,

Each cell can be assigned k channel

Case III: Cellular Networks

NSk /

22 jijiN

N/1

1

2

4

5

6

7

Frequency Reuse Pattern for N=7

3

2

5

6

7

3

4

3

7

7

4

4

4

3

2

5

6

6

1

1

1

1

1

1

Number of cells per cluster:

If M clusters within the system, the total system capacity: MSMkNC

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Case III: Cellular Network

There were several fundamental problems in cellular network when moving to multi-service environment Bandwidth within a cell have to be shared Erlang assumption (Poisson arrival and exponentia

l sojourn time and exponential call duration time) fails due to data traffic

Gaussian approximation for a cell capacity fails given the cell is small …

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Case III: Cellular Network

Relaxing Erlang, by considering heavy tail long range dependency LRD) distribution, i.e., Pareto distribution Failed since 1997

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Case III: Cellular Network

Gaussian approximation Particle movement and diffusion equation S. Wu, K. Y. M. Wong and B. Li, “A Dynamic Call

Admission Policy with Precision QoS Guarantee Using Stochastic Control for Mobile Wireless Networks,” IEEE/ACM Transactions on Networking, (10)2: 257-271, April 2002.

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Summary

Working on hard and open problems Persistence pays off

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Summary

The idea has to be simple, this is a hard lessen we have learn

10 years of research on ATM are pretty much a waste

Internet POTS or PSTN

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Outline

What about research? How much does one have to learn? PhD research What is procedure of publications? How to write technical papers?

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Conference Paper

Start earlier for a conference submission Deadline is the best drive for making progress What make a good paper: content and writing! Clear, convincing, simple and good English

This is a never-ending optimization process, do this within the time and page limits

Review process 5/30 rule 5 minutes - Abstract, introduction, figure and

conclusion 30 minutes – understand 90% of the paper

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Journal Paper

A good conference paper (10%-25% acceptance rate) can be submitted to a journal, with 30% new results

Report more complete and focused results Give yourself a deadline Be patient with the long review and re-review At the earlier stage of one’s career, don’t quit

if asked for major revision But don’t do seemingly impossible

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What does a reviewer look for

New problem or new solution? Are the main results significant? Is the paper technically correct? Does the paper provide a fair assessment of its

strength and limitation? Is the paper clearly written, thus accessible to

general readers? Are the references adequate? Is the paper appropriate for conference/journal? …

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Outline

What about research? How much does one have to learn? PhD research What is procedure of publications? How to write technical papers?

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Writing

Writing is a process of self-clarification Habit of writing, notes, random thoughts

There are plenty of books teaching you how to write Imitation might be the best way to start

Writing is part of the work Writing can be difficult and painful for

all of us, there is no short cut, it improves along the process

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Writing

Iterative refinement, outlines – 3-5 times Start with existing work, introduction, your

own work, experiment Abstract and summary (many hours’ work) Revise many times, ask others to read

Lots of efforts for small improvement Is there a better way to say, a better word to use? Is the paper logically connected? What are the questions reviewers might have?

Never ending optimization subject to time and page limit

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Review Process

Low acceptance rate Reviewers are potential competitors

Convincing but less critical Reviewers are very busy

Try to make their job easier English is not our strength Don’t try your luck, it won’t work!

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Problem I

Reviewers have to understand me Only you know your work well, not

reviewers Make it easier to understand

Motivation and rationales Control the level of details Make connection throughout the paper Use examples, graph, flow chat whenever

needed Pose questions, and answer them

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Problem II

Formality leads to elegance I am good at math, formal is high class, I

have 20 definitions and 15 theorems Keep it simple, perhaps stupid Start with motivations and rationales Avoid unnecessary formality

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Problem III

I have 10 contributions Reviewers should see this is a masterpiece

Focus in the key One problem, one solution in a conference paper One problem, more complete solutions in a journal

paper Thorough and deep

Emphasize but not exaggerate your contributions Say it is “significant” only if it is, and justify it If it is the first time, say “This is, to the best of our

knowledge, the first time … “

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Problem IV

It is ok to be informal as long as understandable Technical writing is formal Avoid casual writing

“believe me, this is really a good work” Don’t use long sentences, break them

Flow and logic is much more important, proof reading does not help you with that

Top-down organization and outlining Use good papers as sample – imitate! Write down your mistakes and eliminate them

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Problem V

Reviewers are evil They reject paper so their papers can be accepted They reject my paper, so to steal my ideas

Reviewers are critical You have to be a good salesman to convince

them

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Closing Thoughts

Research needs creativity, patience, hard working, persistence

Writing is a self-improving process Understanding the process of publication, in

particular review process helps

KEYS Balance the search and re-development and

out-of-box thinking Working with smart people

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Closing Thoughts

We have done so much for networking! 10 years ago: IP vs. ATM Since then

QoS, network Calculi, intServ, diffServ, CNDs, DDoS, VoIP, SIP, multicast TPC, closed-loop control, measurement, LRD traffic, power laws, Streaming, WWW protocols, caching

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Closing Thoughts

Yet this conversation happened in a major research lab (NJ)

Q: given the traffic and network topology, how do we optimize the routes?

A1: “Uh ….”A2: “We don’t really think it that way … “A3: “We don’t know the traffic, we don’t know

the topology, the routers do not automatically adapt to traffic, and we don’t know how to optimize the route configuration. BUT, other than that, we are all set!”

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Closing Thoughts

Don’t believe anything you read, esp., those obviously correct ones!

Challenge the fundamental!

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Acknowledgement

Students, collaborators, and MSRA Charles X. Ling (Univ. of Western Ontario), Qiang Ya

ng (HKUST), Jim Kurose (UMass at Amherst)