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Prof. Robin Kravets
CS/ECE 438: Communication Networks
Spring 2015 1 Copyright ©: CS 438 Staff, University of Illinois
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Copyright notice
n Copyright 2015 by University of Illinois n All rights reserved. Permission to reproduce this
and all ECE/CS 438 course materials in whole or part for not-for-profit educational purposes is hereby granted. This document may not be reproduced for commercial purposes without the express written consent of the author.
n Includes content by Brighten Godfrey, Matthew Caesar, Robin Kravets, Steve Lumetta, Bruce Hajek, Nitin Vaidya, Larry Peterson, Jennifer Rexford, Ion Stoica, and others
Spring 2015 2 Copyright ©: CS 438 Staff, University of Illinois
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Course Information
n Instructor ¡ Prof. Robin Kravets
3114 SC 217-244-6026 [email protected]
n TAs ¡ Frederick Douglas ¡ Qingxi Liao ¡ Guliz Tuncay
n Class Webpage ¡ http://courses.engr.illinois.edu/cs438/
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Course Information
n Use Piazza for all class related communication ¡ Announcements and discussions
n http://www.piazza.com/illinois/cs438 ¡ All class questions ¡ This is your one-stop help-line! ¡ Will get answer < 24 hours
n For personal communications, do not send email ¡ Use the private message function on Piazza
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Course Information
n Text book ¡ Computer Networks: A Systems Approach, by
Peterson and Davie, 5th Ed. (minor differences from 4th edition)
n Supplemental Text books ¡ UNIX Network Programming, by Stevens
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Prerequisites
n Operating Systems Concepts ¡ CS 241 or ECE 391 or equivalent
n Threads, memory management, sockets
n C or C++ Programming ¡ Preferably Unix
n Probability and Statistics
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Grading Policy
n Homework 14% ¡ 7 homework assignments
n Programming Projects 46% ¡ MP0 3%, MP1 11%, MP2 16%, MP3 16%
n Midterm Exam 15% ¡ Week of March 9 (M or T), 7 - 9PM
n Final Exam 25% ¡ TBA
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Homework and Projects
n Homework ¡ 7 homeworks each worth 2% ¡ Due Wednesdays at start of class. ¡ General extension to Fridays start of class (hard deadline).
n Solutions handed out in class on Fridays ¡ No questions to Professor, TAs or on Piazza after class on
Wednesday.
n Projects ¡ Late policy for projects - 2% off per hour late ¡ MP0 and MP1 are solo ¡ MP2 and MP3 are 2 person teams
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Regrades
n Within one week of posting of grades for a homework, MP or exam
n Regrades must be submitted in writing on a separate piece of paper ¡ Please do not write on your homework,
MP or Exam
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Academic Honesty
n Your work in this class must be your own. n If students are found to have cheated (e.g., by copying or
sharing answers during an examination or sharing code for a project), all involved will at a minimum receive grades of 0 for the first infraction. ¡ We will run a similarity-checking system on code and binaries
n Further infractions will result in failure in the course and/or recommendation for dismissal from the university.
n Department honor code: https://wiki.engr.illinois.edu/display/undergradProg/Honor+Code
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What is cheating in a programming class?
n At a minimum ¡ Copying code ¡ Copying pseudo-code ¡ Copying flow charts
n Consider ¡ Did some one else tell you how to do it?
n Does this mean I can’t help my friend? ¡ No, but don’t solve their problems for them
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Graduate Students
n Graduate students MAY take an extra one hour project in conjunction with this class ¡ Graduate students
n Write a survey paper in a networking research area of your choice
n Project proposal with list of 10+ academic references (no URL’s) due February 10th
n Paper due last day of class ¡ Undergraduates may not take this project course
n However, if you are interested in networking research, please contact me
Spring 2015 Copyright ©: CS 438 Staff, University of Illinois 12
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Goal: foundational view of computer networks
n Fundamental challenges of computer networking
n Design principles of computer networks
n From principles to practical protocols n Build real network applications
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Course Contents
n Introduction to UNIX Network Programming n Direct Link Networks n Packet Switched Networks n Routing n Internetworking n End-to-End Protocols n Congestion Control n Mobile Ad hoc Networks n P2P Networks n Network Security n … more if there is time
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Complete Schedule
n See class webpage n http://www.cs.illinois.edu/class/cs438
¡ Schedule is dynamic ¡ Check regularly for updates
n Content ¡ Slides will be posted by the night before class
n Bring a print out of the sides to class n Some class material may not be in slides
¡ Examples may be worked out in class
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What do these two things have in common?
n First printing press
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n The Internet
Both lowered the cost of distributing information and changed human society
[opte.org]
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A Brief History of the Internet
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Visionaries
n Vannevar Bush, “As we may think” (1945): ¡ memex - an adjustable
microfilm viewer n J. C. R. Licklider (1962): “Galactic Network” ¡ Concept of a global
network of computers connecting people with data and programs
¡ First head of DARPA computer research, October 1962
¡ Funded Arpanet
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Bush
Licklider
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Circuit switching
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1920s 1967
[US Air Force]
[Getty Images]
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1961-64: Packet switching
n Leonard Kleinrock ¡ Queueing-theoretic analysis of packet switching in
MIT Ph.D. thesis (1961-63) demonstrated value of statistical multiplexing
n Paul Baran (RAND), Donald Davies ¡ Concurrent work from (National Physical
Labratories, UK)
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Kleinrock
Baran
Circuit switching
Time
Packet switching
Time
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Circuit Switching Datagram packet switching
1961-64: Packet switching
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Circuit Switching Datagram packet switching
Physical channel carrying stream of data from source to destination
Three phase: setup, data transfer, tear-down
Data transfer involves no routing
1961-64: Packet switching
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Circuit Switching Datagram packet switching
Physical channel carrying stream of data from source to destination
Message broken into short packets, each handled separately
Three phase: setup, data transfer, tear-down One operation: send packet
Data transfer involves no routing Packets stored (queued) in each router, forwarded to appropriate neighbor
1961-64: Packet switching
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1965: First computer network
n Lawrence Roberts and Thomas Merrill connect a TX-2 at MIT to a Q-32 in Santa Monica, CA
n ARPA-funded project n Connected with telephone line –
it works, but it’s inefficient and expensive – confirming motivation for packet switching
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Roberts
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The ARPANET begins
n Roberts joins DARPA (1966), publishes plan for the ARPANET computer network (1967)
n December 1968: Bolt, Beranek, and Newman (BBN) wins bid to build packet switch, the Interface Message Processor (IMP)
n September 1969: BBN delivers first IMP to Kleinrock’s lab at UCLA
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An older Kleinrock with the first IMP
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ARPANET comes alive
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Stanford Research Institute (SRI)
“LO” Oct 29, 1969
UCLA
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ARPANET grows
n Dec 1970: ARPANET Network Control Protocol (NCP)
n 1971: Telnet, FTP
n 1972: Email (Ray Tomlinson, BBN)
n 1979: USENET
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ARPANET, April 1971
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And grows …
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77 nodes
How many do we have today?
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ARPANET to Internet
n Meanwhile, other networks such as PRnet, SATNET deveoped
n May 1973: Vinton G. Cerf and Robert E. Kahn present first paper on interconnecting networks
n Concept of connecting diverse networks, unreliable datagrams, global addressing, ...
n Became TCP/IP
Spring 2015 Copyright ©: CS 438 Staff, University of Illinois 29 Kahn
Cerf
2004 Turing Award!
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TCP/IP deployment
n TCP/IP implemented on mainframes by groups at Stanford, BBN, UCL
n David Clark implements it on Xerox Alto and IBM PC
n 1982: International Organization for Standards (ISO) releases Open Systems Interconnection (OSI) reference model
¡ Design by committee didn’t win out n January 1, 1983: “Flag Day” NCP to
TCP/IP transition on ARPANET OSI Reference Model’s layers
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Application
Presentation
Physical
Transport
Session
Data Link
Network
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OSI Protocol Stack
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Application
Presentation
Physical
Transport
Session
Data Link
Network
n Application: Application specific protocols
n Presentation: Format of exchanged data
n Session: Name space for connection mgmt
n Transport: Process-to-process channel
n Network: Host-to-host packet delivery
n Data Link: Framing of data bits
n Physical: Transmission of raw bits
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Growth from Ethernet
n Ethernet ¡ R. Metcalfe and D.
Boggs, July 1976 n Spanning Tree
protocol ¡ Radia Perlman,
1985 n Made local area
networking easy
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Metcalfe
Perlman
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Growth spurs organic change
n Early 1980s ¡ Many new networks: CSNET,
BITNET, MFENet, SPAN (NASA), ...
n Nov 1983 ¡ DNS developed by Jon
Postel, Paul Mockapetris (USC/ISI), Craig Partridge (BBN)
n 1984 ¡ Hierarchical routing: EGP and
IGP (later to become eBGP and iBGP)
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Postel
Partridge
Mockapetris
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NSFNET
n 1984: NSFNET for US higher education ¡ Serve many users, not just one
field ¡ Encourage development of
private infrastructure (e.g., initially, backbone required to be used for Research and Education)
¡ Stimulated investment in commercial long-haul networks
n 1990: ARPANET ends n 1995: NSFNET decommissioned
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NSFNET backbone, 1992
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Explosive growth!
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In users
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Explosive growth!
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In users
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Explosive growth!
Spring 2015 Copyright ©: CS 438 Staff, University of Illinois 37
In hosts
Cisco estimates 21 Billion Devices
in 2018!
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Explosive growth!
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In networks
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Explosive growth! In complexity
ethernet segment
hub
switch
LAN LAN
IP router
Autonomous System
...
BGP router
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spanning tree + learning broadcast
MPLS, CSPF, OSPF, RIP, ...
eBGP, iBGP
Routing protocols
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Explosive growth!
n In technologies ¡ Link speeds 200,000x faster ¡ NATs and firewalls ¡ Wireless everywhere ¡ Mobile everywhere ¡ Tiny devices (smart phones) ¡ Giant devices (data centers)
n In applications ¡ Morris Internet Worm (1988) ¡ World wide web (1989) ¡ MOSAIC browser (1992) ¡ Search engines ¡ Peer-to-peer ¡ Voice ¡ Radio ¡ Botnets ¡ Social networking ¡ Streaming video ¡ Data centers ¡ Cloud computing ¡ IoT
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Explosive growth!
n Every minute of the day ¡ Facebook users share nearly 2.5 million pieces of
content ¡ Twitter users tweet nearly 300,000 times ¡ Instagram users post nearly 220,000 new photos ¡ YouTube users upload 72 hours of new video
content ¡ Apple users download nearly 50,000 apps ¡ Email users send over 200 million messages ¡ Amazon generates over $80,000 in online sales
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Huge societal relevance
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FridayJune 122009
SaturdayJune 13
SundayJune 14
Routing instabilities and outages in Iranian prefixesfollowing 2009 presidential election
Affe
cted
pre
fixes
[James Cowie,Renesys Corporation]
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Affe
cted
pre
fixes
(%
)
Fri, Aug 8, 2008[Earl Zmijewski, Renesys
Corporation]
Huge societal relevance
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Routing instabilities and outages in Georgian prefixes following 2008 South Ossetia War
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Top 30 inventions of the last 30 years
1. Internet/Broadband/World Wide Web 2. PC/Laptop Computers 3. Mobile Phones 4. E-Mail 5. DNA Testing and Sequencing/Human
Genome Mapping 6. Magnetic Resonance Imaging (MRI) 7. Microprocessors 8. Fiber Optics 9. Office Software 10. Non-Invasive Laser/Robotic Surgery 11. Open Source Software and Services 12. Light Emitting Diodes (LEDs) 13. Liquid Crystal Displays (LCDs) 14. GPS 15. Online Shopping/E-Commerce/Auctions
16. Media File Compression 17. Microfinance 18. Photovoltaic Solar Energy 19. Large Scale Wind Turbines 20. Social Networking via Internet 21. Graphic User Interface (GUI) 22. Digital Photography/Videography 23. RFID 24. Genetically Modified Plants 25. Biofuels 26. Bar Codes and Scanners 27. ATMs 28. Stents 29. SRAM/Flash Memory 30. Anti-Retroviral Treatment for
AIDS
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Compiled by the Wharton School @ U Penn, 2009
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Top 30 inventions of the last 30 years
1. Internet/Broadband/World Wide Web 2. PC/Laptop Computers 3. Mobile Phones 4. E-Mail 5. DNA Testing and Sequencing/Human
Genome Mapping 6. Magnetic Resonance Imaging (MRI) 7. Microprocessors 8. Fiber Optics 9. Office Software 10. Non-Invasive Laser/Robotic Surgery 11. Open Source Software and Services 12. Light Emitting Diodes (LEDs) 13. Liquid Crystal Displays (LCDs) 14. GPS 15. Online Shopping/E-Commerce/Auctions
16. Media File Compression 17. Microfinance 18. Photovoltaic Solar Energy 19. Large Scale Wind Turbines 20. Social Networking via Internet 21. Graphic User Interface (GUI) 22. Digital Photography/Videography 23. RFID 24. Genetically Modified Plants 25. Biofuels 26. Bar Codes and Scanners 27. ATMs 28. Stents 29. SRAM/Flash Memory 30. Anti-Retroviral Treatment for
AIDS
Spring 2015 Copyright ©: CS 438 Staff, University of Illinois 45
Compiled by the Wharton School @ U Penn, 2009
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1
10110
11
That’s it! ...right?
Why is Networking Challenging
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11110 01
1011
1 10
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Fundamental Challenge: Speed of Light
n How long does it take light to travel from UIUC to Mountain View, CA (Google Headquarters)?
n Answer: ¡ Distance UIUC –> Mountain View is 2,935 km ¡ Traveling 300,000 km/s: 9.78ms
n Note: Dependent on transmission medium ¡ 3.0 x 108 meters/second in a vacuum ¡ 2.3 x 108 meters/second in a cable ¡ 2.0 x 108 meters/second in a fiber
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Fundamental Challenge: Speed of Light
n How long does it take an Internet “packet” to travel from UIUC to Mountain View?
n Answer: ¡ For sure ≥ 9.78ms ¡ But also depends on:
n The route the packet takes (could be circuitous!) n The propagation speed of the links the packet traverses
¡ e.g. in optical fiber light propagates only at 2/3 C n The transmission rate (bandwidth) of the links (bits/sec)
¡ And also the size of the packet
n Number of hops traversed (“store and forward” delay) n The “competition” for bandwidth the packet encounters (congestion). It may
have to wait in router queues.
¡ In practice this boils down to ≥ 40ms (and likely more) n With variance (can be hard to predict!)
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Performance
n Bandwidth/throughput ¡ Data transmitted per
unit time ¡ Example: 10 Mbps ¡ Link bandwidth vs. end-
to-end bandwidth
¡ Notation n KB = 210 bytes n Mbps = 106 bits per
second
n Latency/delay ¡ Time from A to B ¡ Example: 30 msec ¡ Many applications
depend on round-trip time (RTT)
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Why?
You will mess this up at least once on a HW or exam!
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Delay x Bandwidth Product
n Amount of data in “pipe” ¡ channel = pipe ¡ delay = length ¡ bandwidth = area of a cross section ¡ bandwidth x delay product = volume
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Bandwidth
Delay
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Delay x Bandwidth Product
n Bandwidth x delay product ¡ How many bits the sender must transmit before the first bit
arrives at the receiver if the sender keeps the pipe full ¡ Takes another one-way latency to receive a response
from the receiver
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A B
1
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Delay x Bandwidth Product
n Bandwidth x delay product ¡ How many bits the sender must transmit before the first bit
arrives at the receiver if the sender keeps the pipe full ¡ Takes another one-way latency to receive a response
from the receiver
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A B
1 2
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Delay x Bandwidth Product
n Bandwidth x delay product ¡ How many bits the sender must transmit before the first bit
arrives at the receiver if the sender keeps the pipe full ¡ Takes another one-way latency to receive a response
from the receiver
Spring 2015 Copyright ©: CS 438 Staff, University of Illinois 53
A B
1 3 2
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Delay x Bandwidth Product
n Bandwidth x delay product ¡ How many bits the sender must transmit before the first bit
arrives at the receiver if the sender keeps the pipe full ¡ Takes another one-way latency to receive a response
from the receiver
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Delay x Bandwidth Product
n Bandwidth x delay product ¡ How many bits the sender must transmit before the first bit
arrives at the receiver if the sender keeps the pipe full ¡ Takes another one-way latency to receive a response
from the receiver
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Delay x Bandwidth Product
n Bandwidth x delay product ¡ How many bits the sender must transmit before the first bit
arrives at the receiver if the sender keeps the pipe full ¡ Takes another one-way latency to receive a response
from the receiver
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Delay x Bandwidth Product
n Bandwidth x delay product ¡ How many bits the sender must transmit before the first bit
arrives at the receiver if the sender keeps the pipe full ¡ Takes another one-way latency to receive a response
from the receiver
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Delay x Bandwidth Product
n Bandwidth x delay product ¡ How many bits the sender must transmit before the first bit
arrives at the receiver if the sender keeps the pipe full ¡ Takes another one-way latency to receive a response
from the receiver (round trip BxD)
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Delay x Bandwidth Product
n Example: Transcontinental Channel ¡ BW = 45 Mbps ¡ delay = 50ms ¡ bandwidth x delay product
= (50 x 10–3 sec) x (45 x 106 bits/sec) = 2.25 x 106 bits
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ms Mbps
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Bandwidth vs. Latency
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n Relative importance ¡ 1-byte: Latency bound
n 1ms vs 100ms latency dominates 1Mbps vs 100Mbps BW ¡ 25MB: Bandwidth bound
n 1Mbps vs 100Mbps BW dominates 1ms vs 100ms latency
25MB 1 Mbps
1B
1Mbps
1ms
100 Mbps 1Mbps
100ms
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Bandwidth vs. Latency
n Infinite bandwidth ¡ RTT dominates
n Throughput = TransferSize / TransferTime n TransferTime = RTT + 1/Bandwidth x
TransferSize
n Its all relative ¡ 1-MB file on a 1-Gbps link looks like a 1-
KB packet on a 1-Mbps link
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Fundamental Challenge: Speed of Light
n How many cycles does your PC execute before it can possibly get a reply to a message it sent to a Mountain View web server?
n Answer ¡ Round trip takes >= 80ms ¡ PC runs at (say) 3 GHz ¡ 3,000,000,000 cycles/sec * 0.08 sec = 240,000,000 cycles
n Thus ¡ Communication feedback is always dated ¡ Communication fundamentally asynchronous
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Fundamental Challenge: Speed of Light
n What about machines directly connected (via a local area network or LAN)?
n Answer: % ping www.cs.uiuc.edu
PING dcs-www.cs.uiuc.edu (128.174.252.83) 56(84) bytes of data.64 bytes from 128.174.252.83: icmp_seq=1 ttl=63 time=0.263 ms64 bytes from 128.174.252.83: icmp_seq=2 ttl=63 time=0.595 ms64 bytes from 128.174.252.83: icmp_seq=3 ttl=63 time=0.588 ms64 bytes from 128.174.252.83: icmp_seq=4 ttl=63 time=0.554 ms...
n 500us = 1,500,000 cycles ¡ Still a loooooong time…
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Fundamental Challenge: Shared infrastructure
n Different parties must work together ¡ Multiple parties with different agendas must agree how to
divide the task between them
n Working together requires ¡ Protocols (defining who does what)
n These generally need to be standardized ¡ Agreements regarding how different types of activity are
treated (policy)
n Different parties very well might try to “game” the network’s mechanisms to their advantage
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Fundamental Challenge: Shared infrastructure
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n Physical links and switches must be shared among many users
n Common multiplexing strategies ¡ (Synchronous) time-division multiplexing (TDM) ¡ Frequency-division multiplexing (FDM)
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Fundamental Challenge: Shared infrastructure
n Statistical Multiplexing (SM) ¡ On-demand time-division multiplexing ¡ Scheduled on a per-packet basis ¡ Packets from different sources are
interleaved ¡ Uses upper bounds to limit transmission
n Queue size determines capacity per source
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Fundamental Challenge: Shared infrastructure
n Packets buffered in switch until forwarded n Selection of next packet depends on policy
¡ How do we make these decisions in a fair manner? Round Robin? FIFO?
¡ How should the switch handle congestion?
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Fundamental Challenge: Things break
n Communication involves a chain of interfaces, links, routers, and switches… ...stitched together with many layers of software... ...all of which must function correctly!
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Fundamental Challenge: Things break
n Suppose a communication involves 50 components that work correctly (independently) 99% of the time.
n What’s the likelihood the communication fails at a given point in time? ¡ Answer: success requires that they all function, so failure
probability = 1 – 0.9950 = 39.5%
n So we have a lot of components, which tend to fail… ¡ … and we may not find out for a loooong time
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Fundamental Challenge: Enormous dynamic range
n Challenge: enormous dynamic range ¡ Round trip times (latency) 10 us’s to sec’s (105) ¡ Data rates (bandwidth) kbps to 10 Gbps (107) ¡ Queuing delays in the network 0 to sec’s ¡ Packet loss 0 to 90+% ¡ End system (host) capabilities cell phones to clusters ¡ Application needs: size of transfers,
bidirectionality, reliability, tolerance of jitter
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Fundamental Challenge: Enormous dynamic range
n Challenge: enormous dynamic range
n Related challenge: very often, there is no such thing as “typical” ¡ Beware of your “mental models”! ¡ Must think in terms of design ranges, not points ¡ Mechanisms need to be adaptive
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Fundamental Challenge: Constantly Changing
n Incessant rapid growth ¡ Decades of exponential growth ¡ Data centers contain hundreds of
thousands of hosts, Internet contains billions of hosts, millions of routers
¡ Microsoft’s data center in Chicago: 500k servers
¡ Bandwidth 10x cheaper in 4 years ¡ (commercial CDN prices)
n Adds another dimension of dynamic range… ¡ and quite a number of ad hoc artifacts…
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[Ion Stoica, Conviva]
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Fundamental Challenge: Security
n Challenge: there are Bad Guys out there! n Early days
¡ Vandals ¡ Hackers ¡ Crazies ¡ Researchers
n As network population grows, it becomes more and more attractive to crooks
n As size of and dependence on the network grows, becomes more attractive to spies, governments, and militaries
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Fundamental Challenge: Security
n Attackers seek ways to misuse the network towards their gain ¡ Carefully crafted “bogus” traffic to manipulate the
network’s operation ¡ Torrents of traffic to overwhelm a service (denial-of-
service) for purposes of extortion/competition ¡ Passively recording network traffic in transit (sniffing) ¡ Exploit flaws in clients and servers using the network to
trick into executing the attacker’s code (compromise)
n They all do this energetically because there is significant $$$ to be made
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The Ultimate Challenge
n Cannot reboot the Internet ¡ Everyone depends on the Internet
n Businesses n Hospitals n Education institutions n Financial sector n …
n Fixing the Internet akin to changing the engine while you are flying the plane!
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Why Networking is Challenging
n Tubes: not entirely wrong, but simplistic
n How do we build a communication infrastructure for all of humanity?
n Must design for extreme heterogeneity across technology, applications, users
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What’s next
n MP 0 ¡ Available Friday ¡ Sockets refresher
n HW 1 ¡ Available Friday
n Friday ¡ UNIX network programming
n Next week ¡ Technical overview of Internet architecture ¡ Data link technologies
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