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/
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