lecture on mass media society

7/29/2019 Lecture on Mass Media Society

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CS211: Protocol and SystemsDesign for Wireless and MobileNetworks

Instructor: Songwu [email protected]

Office: 4531D BH

Lectures: 2:00-3:50am M&Woffice hours: 4:00-5:00pm M&W


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What this course is about...

Introduce

Internet design philosophy

Wireless networking protocols

Mobile computing system software design

Trendy topics

System programming skills

How to start research


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Networking fundamentals: Internet

philosophy and principles

Wireless Protocols-MAC protocol-802.11 Standard

- Scheduling

- Mobility management, ad-

hoc routing

- wireless TCP

Mobile Computing

- middleware, OS, file sys.

- services, applications

Topical Studies-Wireless security-Sensor networks

-QoS and Energy-efficient

design-Mesh Networks

-MIMO Systems

A picture of the course coverage


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Emerging Wireless Networks

Base Station

Fixed Host

Wireless Cell

Internet

Backbone

Mobile Host


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Growth of Wireless Users

010203040506070

1991 1993 1995 1997

Wireless Phone Subscribers (in millions)

Source: cellular telecom. Indus. Assn.

02468

1012

1997 1998 1999 2000 2001 2002

Wireless Data Subscriber (in millions)

Source: Strategis Market Res.


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The Wi-Fi Space

It is one of the fastest growing industrysectors

100,000 public hotspots by 2005

Most notebooks will have embedded wi-fi card

Go and check the local hotspots online www.ezgoal.com/hotspots/


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Protocol Stack Wireless Web, Location

Services, etc.

Content adaptation,

Consistency, File system

Wireless TCP

Mobility, RoutingQoS

o Scheduling

o MAC

Application Layer

Middleware and OS

Transport Layer

Network Layer

Link Layer & Below


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The Course Description

No required textbook for this course, only aset of papers

Read and discuss

your class participation counts

practice what you have learned get your hand dirty: do a term project

make your contributions

Heavy workload expectedYou are expected to be prepared for each lecture

by reading the paper BEFORE coming to thelecture


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Prerequisites

basic knowledge of packet switchednetworks & familiarity with TCP/IP

protocol suite adequate programming experience

familiar with C/C++/UNIX

useful reference books: Internetworking with TCP/IP, Vols I, II, III

by Doug Comer

TCP/IP Illustrated, Vols 1 & 2 by Stevens


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Course Workload

One midterm, no final exam Midterm: November 10th, in class.

reading assignment:

1~2-page summary for the assigned reading ofeach lecture

3 strong points, 3 weak points, suggestions

Similar to the paper review process you are going

to do for your field in the future all assignments due 12:00pm(noon) before

lecture on the due date email to [email protected] with subject cs211:

homework #


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Course Project

A few big projects

Several topics within each big project to be

distributed this Wednesday 2-3 persons on each topic

Pick a topic and a team by next Monday

Proposal + Checkpoint + Presentation+ Final Report


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Why such projects?

Interact closely within your topic team

Discuss every three weeks within your

big project to have the big picture inmind

Stimulate discussions across teams

Most topics are well defined, and youhave a good starting point


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Grading PolicyGrading breakdown:

in-class presentation: 10% 5~10 min each person

Will get an assigned paper (expanding the topicscope of the paper discussed in class) from me

midterm exam: 30%

homework assignments: 20% There would be 19 assignments, you are expected

to turn in at least 15

The 15 critiques with highest scores to be counted

term project: 40% proposal 5%, checkpoint 10%, final report 15%,

presentation & demo 10%


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Course policies

Homeworks, project proposals & reports alldue 12:00pm on the due date

No late turn-in accepted for credit!!!

No makeup exam!!!

Course homepage:

http://www.cs.ucla.edu/classes/fall03/cs211/

[email protected]
mailto:[email protected]:[email protected]


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Tips on Doing Research in Graduate School

1. How to do productive research in graduate school

2. What are the bad practices you should avoid

3. Your feedback?


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The content of this presentation

We take slides and points from many outstandingresearchers: Dave Patterson, Richard Hamming, CraigPatridge, Nitin Vaidya, and the many references andsources cited there. They deserve all the credits

I also share some of my own experiences

We need your input and feedback too


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Caveats

Only opinions from some people. Othersmay not agree, including your advisors.

Use advice at your own risk

I do not necessarily follow the advice all

the time This presentation may not follow some

rules it talks about


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What is Research, Anyway?

Research is not really about coming up with a nice solutionto a hard (possibly new) problem, to show how smart youare.

It is a process:

identifying a research problem Coming up with a nice/new result (including simulating,

implementing, testing your solution)

Writing your results well

Presenting your results

Marketing your work

Engineering is not science, it is about different tradeoff (whether ucan do things easier, efficient, more convenient, at acceptablecost/complexity), precisely true/false is not the main concern


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A Few EQ Rules

Motivation: you are indeed interested in PhD research

Think carefully about your career goal when you start your PhD

NOT: My family asks me to get a PhD, It is hard to find a job with a MSdegree now, I want to hang around in school a little longer

We can get you interested in something for some time, but not all the time

Good start: well begun, half done

Work harder during the first two years to settle down in research

Have a taste of what is good research; not poisoned by the bad taste

Believe yourself: your mindset has not be framed by conventionalapproaches yet; you can be innovative since you do not know much

You have more energy and can have less distraction at this time

Take the initiative: you do care about what you are working on

Do not be afraid to talk to your advisor or others, and let people know thenegative results/setbacks etc.

If u do not talk to these folks, who can u talk to??? disconnected communication causes more confusion among people

Be honest to research and yourself; do not hide the nasty findings. If you donot understand something, ask; then you will know it.

The reality of capture effect: Each advisor has more students than (s)he canhandle; whoever is more aggressive gets more feedback more output

Push for the project schedule from your side: call for meetings, set deadlines

for internal drafts, look for places where to publish, etc.


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EQ Rules (Contd)

Regular life: manage your time and life properly

Shift from deadline scheduling to priority scheduling

Evaluate your progress periodically. No one else will tell youthat you are not efficient

Have a to-do list on a daily/weekly/monthly basis

Keep your most productive time-slot during a day to yourself

No interruption even by your advisor, full concentration

Even when the deadline comes


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How to put yourself into the best position?

Keep yourself informed and networked: know what is going on

and talk to people

Know the literature on the topic you are working on; not let us tellyou what to read. A quick rule 10+10 for breadth and depth: ten topsystems/network conferences and ten leading groups

People networking: the best way to be a missionary for your work

Conference is a best place to talk to people. Do not spend most time to

polish your slides/talk there!! When people contact you for your work, be responsive. If you do not

care about your work, who should care?

Attend seminars: people present the meat and dark side of theirwork in a talk

Balance between quality and quantity: make your recordwithout controversy

Target a top conference each year: show your work quality

Try at least a couple of small conferences: show your productivity

Good way to practice writing, independent research, presentation,

A nice way to go to scenery places for sightseeing, vacations


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Selecting a Problem Solve a real problem that sb. cares about

Follow the industry technology trend and try to stay ahead

of it a little Bad move: even if technology appears to leave you behind, stand by

your problem

Bad move: avoid payoffs of less than 20 years

Working on a new problem is always easier

People have worked on some problems, e.g., congestion control, foryears. It is debatably harder for you to jump in and make majorcontributions

Select a topic that you are interested for some extendedperiod of time, not just for a month

Interdisciplinary topics are always better, they can be veryfruitful

Running real experiments to discover new problems

For systems topic, start from yourself: what do you need the

systems to do for you?

C i ith l ti


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Coming up with a solution Do not rush for a solution simply based on the literature or what others tell

you

Understand the problem better, the solution naturally follows

Use common sense Do not try to simply combine several existing solutions

Explore new approaches: the alternative/opposite first

Ask questions based on your intuition

Keep things simple unless a very good reason not to

Pick innovation points carefully Best results are obvious in retrospectAnyone could have thought of that

Complexity cost is in longer design, construction, test, and debug

Fast changing field + delays => less impressive results

Bad move: best compliment: it is so complicated, I cannot understand

the ideas Best solutions are a combination of simplicity and depth

Keep the solution core simple

Depth is on second-level issues and fixes

A relevant issue: How do I know mine is different from others

READING PAPERS


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How to read a paper?

Know why you want to read the paper

To know whats going on

title, authors, abstract

Track a few leading groups/researchers in your area, typicallyless than 10 is enough

Only a few conferences (and journals): sigcomm, mobicom,infocom, sosp, sigmetrics, mobisys,

Papers in your broad research area

introduction, motivation, solution description, summary,

conclusions

sometimes reading more details useful, but not always

Papers that are directly relevant to your work

read entire paper carefully, and several times


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What to note

Authors and research group

Need to know where to look for a paper on particular topic

Theme of the solution Should be able to go back to the paper if you need more info

Approach to performance evaluation

Note any shortcomings

Be critical. It is easy to say nice words about a work, it isharder to identify limitations/flaws

I th f h


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Get Periodic Reviews/Feedbacks with OthersTalk to people and ask what they think

Give a seminar within your groupperiodically to collect feedback

Explain the results to your friends, seewhether they can grasp your problem andyour solution

For both technical people and non-technicalpeople

Exchange emails, publish technical reports

In the process of a researchproject


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Evaluate Quantitatively If you cant be proven wrong, then you cant prove youre right

Report in sufficient detail for others to reproduce results

cant convince others if they cant get same results

For better or for worse, benchmarks shape a field

Good ones accelerate progress

good target for development Bad benchmarks hurt progress

help real users v. help sales?

Before you run real experiments, do an intuitive analysis

Math does not need to be fancy, as long as it proves thepoint; in fact, best theory starts from scratch, not from somecomplex theorem you never heard about


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Marketing Publishing papers is not equivalent to marketing

Missionary work: Sermons first, then they read papersSelecting problem is key: Real stuff

Ideally, more interest as time passes

Change minds with believable results

Dave Pattersons experience: industry is reluctant to embrace

changeHoward Aiken, circa 1950:

The problem in this business isnt to keep people from stealingyour ideas; itsmakingthem steal your ideas!

Need 1 bold company (often not no. 1) to take chance andbe

successful RISC with Sun, RAID with (Compaq, EMC, )

Then rest of industry must follow

Publicize software: when people use your tools, they know yourresults

think about how ns-2 and its wireless extension evolve


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How to write a paper

Do unto others as you would have them do unto you When you have truly exceptional results

P == NP

Probably doesnt matter how you write, people will read

it anyway Most papers are not that exceptional

Good writing makes significant difference

Better to say little clearly, than saying too much

unclearly


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Readability a must

If the paper is not readable, author has not given writingsufficient thought

Two kinds of referees

If I cannot understand the paper, it is the writers fault

If I cannot understand the paper, I cannot reject it

Dont take chances. Write the paper well.

Badly written papers typically do not get read


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Do not irritate the reader

Define notation before use

No one is impressed anymore by Greek symbols

If you use much notation, make it easy to find

summarize most notation in one place

Avoid Using Too Many Acronyms AUTMA ?!

You may know the acronyms well. Do not assume

that the reader does (or cares to)


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Writing a draft

First read Strunk and White, then follow these steps;

1. 1-page paper outline, with tentative page budget/section

2. Paragraph map

1 topic phrase/sentence per paragraph, handdrawn

figures w. captions

3. (Re)Write draft

Long captions/figure can contain details ~ Scientific American

Uses Tables to contain facts that make dreary prose

4. Read aloud, spell check & grammar check(MS Word; Under Tools, select Grammar, select Options, select

technical for writing style vs. standard; select Settings and select)5. Get feedback from friends and critics on draft; go to 3.

www.cs.berkeley.edu/~pattrsn/talks/writingtips.html


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How to write a systems paper

Provide sufficient information to allow people to reproduceyour results

people may want to reproduce exciting results

do not assume this wont happen to your paper

besides, referees expect the information

Do not provide wrong information

Sometimes hard to provide all details in available space

may be forced to omit some information

judge what is most essential to the experiments

cite a tech report for more information


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Discuss related work

Explain how your work relates to state of the art

Discuss relevant past work by otherpeople too

Remember, they may be reviewing your paper.

Avoid: The scheme presented by FOO performs terribly

Prefer: The scheme by FOO does not perform as well inscenario X as it does in scenario Y

Avoid offending people, unless you must


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Tell them your shortcomings

If your ideas do not work well in some interesting scenarios,tell the reader

People appreciate a balanced presentation


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How to write weak results

If results are not that great, come up with better ones

Do not hide weak results behind bad writing

Be sure to explain why results are weaker than you expected

If you must publish: write well, but may have to go to second-

best conference Only a few conferences in any area are worth publishing in

Too many papers in poor conferences bad for your reputation

Just because a conference is IEEE or ACM or Internationaldoes not mean it is any good

If results not good enough for a decent conference, rethinkyour problem/solution


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Miscellaneous

Read some well-written papers

award-winning papers from conferences

Avoid long sentences

If you have nothing to say, say nothing

dont feel obliged to fill up space with useless text

if you must fill all available space, use more line spacing,greater margins, bigger font, bigger figures, anything but drivel


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How to present a poster

Answer Five Heilmeier Questions

1. What is the problem you are tackling?2. What is the current state-of-the-art?

3. What is your key make-a-difference concept or technology?

4. What have you already accomplished?

5. What is your plan for success?

Do opposite of Bad Poster commandments Poster tries to catch the eye of person walking by

9 page poster might look like

ProblemStatement

State-of-the-Art

KeyConcept

Accomplish-ment # 1

Title andVisual logo

Accomplish-ment # 2

Accomplish

-ment # 3

Plan for

Success

Summary &

Conclusion


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How to present a paper(at a conference)

Objectives, in decreasing order of importance Keep people awake and attentive

everything has been tried: play fiddle, cartoons, jokes

in most cases, extreme measures should not be needed

humor can help

Get the problem definition across

people in audience may not be working on your problem

Explain your general approach

most productive use of your time

Dirty details

most people in the audience probably do not carea typical conference includes 30+ paper presentations,

yours could be the N-th


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How many slides?

Depends on personal style

Rules of thumb

1 slides for 1-2 minutes Know your pace

I tend to make more slides than I might need, and skip thenot-so-important ones dynamically

Anticipate technical questions, and prepare explanatoryslides


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How to present a paper

Practice makes perfect (or tolerable)

May need several trials to fit your talk to available time

particularly if you are not an experienced speaker

English issue

Accent may not be easy to understand

Talk slowlyEasier said than done

I have a tough time slowing down myself


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The rest of the notes

Overview/Review:

Internet protocol stack

IP protocol

TCP protocol

If you forget these materials, go back andreview what you learned in CS118 ASAP


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Packet Switched Networks

Hosts send data in packets network supports all data communication

services by delivering packets

Web, email, multimedia

Host Host

Application

Host

Web

Host Host

video

email


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One network application example

[email protected] [email protected]

msg


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What is happening inside ?

[email protected] [email protected]

Physical net physical netPhysical net

Network

protocol

Network

protocol

Network

protocol

Network

protocol

Transport

protocol

Transport

protocol


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A B C

network topology

Layered Network Architecture

network consists of geographicallydistributed hosts and switches (nodes)

Nodes communicate with each other by

standard protocols

B

A C

physical connectivity

Protocol layers

D

host switch


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Ethernet frame

network packet

Transport segment

header tail

header

header

DATA

DATA

data

Whats in the header: info needed for the protocols function

Application (data)

B

A

physical connectivity

a picture of protocol layers


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TCP/IP Protocol Suite

IP Protocol: Inter-networking protocol

RFC791

TCP Protocol: reliable transport protocol RFC793


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Why IP

a number of different networktechnologies developed in early 70s:

ARPAnet, Ethernet, Satnet, PRnet

different trans. media: copper, radio,satellite

different protocol designs, e.g.

ARPAnet: reliable message delivery Ethernet: unreliable packet delivery

under different administrative control


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Fundamental Goal of IP

developing an effective technique formultiplexed utilization of all existing

networks no centralized control

no changes to individual subnets

To read next timeThe Design Philosophy of Internet Protocols

by Dave Clark, SIGCOMM'88


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transport

(end-to-end)

subnets

ethernet token-ring FDDI dialup ATM

IP

TCP UDP

inter-network layer

application protocols

transport layer protocols

universal datagram delivery

hardware-specific

network technologies

The picture of the world

according to IP


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IP Packet Header Formatvers. IHL Type-of-Service total length

identifier fragment offset

time-to-live protocol checksum

source address

destination address

options (variable length) padding

data

DFMF


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IP: two basic functions

a globally unique address for eachreachable interface

datagram delivery from any host to any

other host(s)

two supporting protocols

ICMP (Internet Control Message Protocol)

ARP (Address Resolution Protocol)


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Fundamental challenge: How to

scale better Original design: two levels of hierarchy,

network, host

Observed problems: class-based address assignment infeasible

too many networks visible at the top level

two approaches: subnetting & (CIDR)supernetting


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Longer-Term Scaling issues

We've run out of all IPv4 unicast space far before theoretical limit of 4 billion hosts, due to

inevitable inefficiency of address block allocation

Short term patch: NAT boxes

One long term solution: IP version 6 expanded addressing capability: 16 bytes

cleanup of IPv4 design after 15 years of runningexperience

improved support for options/extensions


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The IPv6 Header

Destination Address

Version Priority Flow Label

Payload Length Next Header Hop Limit

Source Address

32 bits


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The IPv4 Header

shaded fields are absent from IPv6 header

Version Hdr Len Total Length

Identification Fragment Offset

Prec TOS

Time to Live Protocol Header Checksum

Flags

Source Address

Destination Address

PaddingOptions

32 bits

TCP T i i C l P l


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TCP: Transmission Control Protocol

a transport protocol IP delivers packets from door to door TCP provides full-duplex, reliablebyte-stream

delivery between two application processes

Application process

Write

bytes

TCP

Send buffer

Application process

Read

bytes

TCP

Receive buffer

segment segment

More terminology:TCP segment

Max. segmentsize (MSS)

TCP j f i li i


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TCP: major functionalities Header format Connection Management

Open, close State management

Reliability management Flow and Congestion control

Flow control: Do not flood the receivers buffer Congestion control: Do not stress the network by

sending too much too fast

f


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u a p r s fr c s s y ig k h t n n

source port destination port

Data sequence number

acknowledgment number

Hlen unused window size

checksum urgent pointer

Options (viable length)

0 16 31

TCP header format

data

IP header

i ti


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client

server

open request(x)

Passive open

ack(x+1) + request(y)

ack(y+1)

(now in estab. state)enter estab. state

opening a connection:three-way hand-shake

Cl i TCP C ti


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Done, delete conn. state

Closing a TCP Connection

I-finished(M)

I-finished(N)

ACK (M+1)

ack(N+1)

wait for 2MSLbefore deleting

the conn state

Mechanisms for Reliability


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Mechanisms for ReliabilityManagement

Sequence number

Acknowledgment number

Error detection at the receiver side Retransmission timeout


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TCP Flow and Congestion Control Window-based protocol

Flow control is easy: set the senderswindow no larger than the advertisedwindow by the receiver

4 algorithms in TCP congestion control

Control congestion window variable: cwnd

slow start, congestion avoidance, fast

retransmit and fast recovery, retransmissionupon timeout

Sender_window=min(adv_win, cwnd)


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Slow Start & Congestion Avoidance

start conservatively: cwnd


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Fast Retransmit

When the 3rd DUP_ACK is received,ssthresh=max(FlightSize/2, 2*SMSS)

ReXmit the lost segment, setcwnd=ssthresh+3*SMSS

Design questions:

why FlightSize, not cwnd ?FlightSize: data sent but not yet acked

Why add 3 SMSS to cwnd ?


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Fast Recovery

For each additional DUP_ACK:

cwnd+=SMSS; (why ?)

transmit a new segment if min(cwnd, rwnd)

permits

When a NEW ACK arrives,

cwnd=ssthresh; (why ?)

Retransmission Timeout


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Retransmission Timeout

Initial design:

RTT=*old_RTT+ (1-)*New_RTT_sample RTO= *RTT; = 2 for original spec

variation in RTT: ~1/(1-L); factor 4, for L=50%;factor 10, for L=80%; load


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Karn s Algorithm

how to measure RTT in retransmission

cases? take the delay between the first (last)

transmission and final ack?

do not update SRTT in case of retransmission? Karns algorithm:

do not take RTT samples in case of

retransmission double the retransmission timer for next

packet, till one can get a RTT sample withoutretransmission


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Putting all together: RFC2581

how TCP congestion control works

Start with slow startfor bootstrapping phase:quickly open up the window

At ssthresh, switch to congestion avoidance When 3rd duplicate ACK is received (indicating

a packet loss), use fast retransmit; if morethan 3 duplicate ACKs, use fast recovery

Upon retransmission timeout (indicating apacket loss too): cwnd=1, binary exponentialbackoff

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