1. Course Overview and Introduction
Nick Feamster CS 6250: Computer Networking Fall 2011

2. Who Am I? Nick Feamster Office: Klaus 3348 Questions: Use Piazza Q&A
Associate Professor
Research Area: Networking Operations and Security
Office: Klaus 3348
Questions: Use Piazza Q&A
Office Hours: Wednesdays 12-1 p.m.
TAs: Srikanth Sundaresan, Surya Sivakumar

3. It’s an Exciting Time More people More global More “things”
Today: 1.9B users
2020: 5B users
More global
Africa, India: ~7% penetration
More “things”
More traffic
44 exabytes by 2012
Fewer wires
Source: internet world stats
Transit prices in Kenya have dropped to $120/Mbps – about what they were in the US in about m indians use the internet (7%), but 500m own mobile phones/SIM cards

4. It’s Also a Critical Time
As much as 95% of traffic is spam
Spam moving to new domains such as Twitter
About 50k new phishing attacks every month
Nearly 60 countries censor Internet content

5. New Technology and Innovation
70% of facebook now outside of the united states (pingdom, jan 2011)
110 million tweets per day (200 M users).
4.5 Billion GSM. WCDMA subscriptions (source: gsacom)
…but, much of this innovation is actually coming from industry.

6. Meanwhile…A Crisis of Confidence
“We don’t need a course in networking; it is all details and no principles.”
“You can’t actually deploy any new technology; Cisco holds the keys to innovation.”
“What are the top ten classic problems in networking?  I would like to solve one of them and submit a paper to SIGCOMM.” After hearing that we don't have such a list: "Then how do you consider networking a discipline?”
“So, these networking research people today aren't doing theory, and yet they aren't the people who brought us the Internet.  What exactly are they doing?”
“Networking is an opportunistic discipline.”

7. Why Has It Been So Difficult?
Network applications (and threats) evolve
Developments call for changes to the network itself
Testing new technologies is challenging
Convince a network operator to “try something out”?
What if the change requires universal deployment?
Deploying new technologies is more challenging
And things are getting worse, not better

8. Difficult to deploy solutions that require fundamental change.
How Did We Get Here?
Internet design came from a different era
Single group of cooperative designers
Cohesive network
Trusted group of users
The reality today is much different
Independently operated networks
Business realities
Untrusted parties with competing goals
Difficult to deploy solutions that require fundamental change.

9. How can networking research turn the tables?
Yesterday’s networking researchers developed technologies to improve the operation of existing networks. (Reactive approach)
Tomorrow’s networking researchers should develop technologies that enable evolution and innovation. (Proactive approach)
Images: band-aid & hammer/crystal ball
We have the plumbers and users. We need the architects.

10. Our Current Thinking: Network as Artifact
“There is a tendency in our field to believe that everything we currently use is a paragon of engineering, rather than a snapshot of our understanding at the time.  We build great myths of spin about how what we have done is the only way to do it to the point that our universities now teach the flaws to students (and professors and textbook authors) who don't know better.”
-- John Day

11. Instead: Could we change the network as easily as applications?
TCP/IP Header in Lego Format.

12. Home Networking & Access Networks
Problems
Performance problems are difficult to debug
Access ISPs discriminate, give poor performance
Hard to manage, troubleshoot, secure
Research
Programmable gateways in homes
Perform active and passive measurements
Collect information about user behavior
Remotely control, troubleshoot, and secure
Project ongoing with FCC
Home networks are difficult for experts to debug, let alone average home users. As we have recently seen in the news, the Federal Communications Commission has also taken an interest in benchmarking access ISP performance in the US, pursuing a deployment of measurement devices in more than 10,000 homes across the country to measure access network performance from various vantage points. We are collaborating with the FCC in this effort: we have analyzed a similar dataset for home network users in France and are now cooperating with the FCC to deploy programmable gateways in homes around the United States. These boxes (shown on the slide) perform a combination of active and passive measurements of both the access link, and of performance inside the home. This allows us to answer interesting questions such as: Where is the cause of performance degradation that a home user is experiencing (e.g., on the access link or inside the home)? We are also collaborating with professors in HCI (Keith Edwards) to understand user behavior (e.g., how users respond to poor performance).

13. Anti-Censorship Problems Research Censorship in 23 countries worldwide
Even in the US!
Existing techniques are not deniable
Research
Exploiting different media for cover traffic (e.g., user-generated content)
Bootstrapping and incentives
Designing better resistance to coercion
Use of social networks
Our tool, Collage, featured in New Scientist
More than 23 countries around the world actively censor Internet content. Even the United States has seen examples of law enforcement shutting down Web sites that are somehow deemed objectionable. Towards enabling the free flow of information on the Internet, we are developing techniques to circumvent censorship firewalls, such as those in China and Iran. Our latest tool, Collage, hides censored content in material that is hosted user-generated content sites, such as Flickr or Picasa (small “chunks” of files are hidden inside photos). We are looking to expand on these techniques, and also to provide better techniques for bootstrapping (i.e., distributing the anti-censorship software).

14. Programmable Networking
Problems
Networks are difficult to configure, manage, secure
Detecting and preventing errors
Predicting the outcome of a configuration
Research
Analysis of existing network configurations
Design of high-level languages for configuring and programming networks
Design and prototyping of new programmable network devices
Frequently Changing Configuration Commands
Networks are difficult to configure, manage, and secure. Network operators make tens to hundreds of changes to low-level network device configurations every day (the tag cloud on the slide shows the frequency of changes for various configuration types: access control lists are among the most common). Two major challenges with network configuration are detecting and preventing errors, and predicting the outcome of a configuration on network behavior. We are working to tackle these problems by (1) analyzing existing network configurations to help us better understand the nature of configuration changes and tasks; (2) designing high-level languages and network controllers to make it easier for operators to configure and debug networks; (3) designing new, open programmable networking devices that allow a protocol designer to easily evolve and develop network protocols (a marked departure from Cisco’s closed and proprietary network devices).

15. Why Networking is Fun You can apply many different “tools”
Theoretical foundations
Statistics, machine learning, signal processing, data mining, etc.
You can build cool systems that people use
Real, working systems that people want and need
Solving real problems (network management, anti-censorship, fighting spam, etc.)
You can measure and explore
Measurement puts the “science” in computer science

16. Why Networking is (More) Fun
Young, relatively immature field
Great if you like to make order out of chaos
Tremendous intellectual progress is still needed
Defining the problem is a big part of the challenge
Recognizing a need, formulating a well-defined problem is at least as important as solving the problem.
Lots of platforms for building your ideas
Programmability: Click, OpenFlow/NOX, NetFPGA
Routing software: Quagga, XORP, and Bird
Testbeds: Emulab, PlanetLab, Orbit, GENI, …
Measurements: RouteViews, traceroute, Internet2, …
The “lots of platforms” is relevant to the course, where we will leverage these platforms to Do Great Things.

17. Meanwhile, back in the classroom…

18. How Practitioners Learn Networking
Certification courses
On how to configure specific pieces of equipment
“On the job” training
Aka “trial by fire”

19. How Universities Teach Networking
Undergraduates: how the Internet works
Graduates: read the 20 “best” papers
Few general principles, little “hands-on” experience
“There is a tendency in our field to believe that everything we currently use is a paragon of engineering, rather than a snapshot of our understanding at the time.  We build great myths of spin about how what we have done is the only way to do it to the point that our universities now teach the flaws to students (and professors and textbook authors) who don't know better.” -- John Day
No need to be too apologetic here. This is a reflection of where we are as a field. The key point is not that we should feel bad about this, but rather than we should not be satisfied with the current state of our understanding.

20. How Did We Get Here? Internet design came from a different era
Single group of cooperative designers
Cohesive network
Trusted group of users
The reality today is much different
Independently operated networks
Business realities (remember depeering)
Untrusted parties, often with competing goals

21. Difficult to deploy solutions that require fundamental change.
The Impasse
Difficult to deploy solutions that require fundamental change.
How many can be easily solved?
How many of these problems require fundamental change?

22. Why We Are at an Impasse Testing new architectures is challenging
How to convince a network operator to “try something out”?
…especially if the change requires universal deployment
Deploying new architectures is more challenging
And things are getting worse, not better
Worse yet, we don’t even know what those new archiectures should be (or whether they are necessary)
So, we tend to teach networking courses as though the protocols, architectures, etc. are fixed. The reality is different. The network is evolving.

23. This Course: A New Approach
Similar material, different organization
Rather than studying “layer-by-layer”, we will look at different problems in networking
We will study different approaches to the same problem and debate their merits
Will study this in the context of different types of networks

24. Logistics Course Web page Course mailing list
Check this page regularly for updates to the syllabus, assignments, readings, etc.
Course mailing list
Run through T-Square
Questions to staff members (instructor, TA)

25. Syllabus Overview Approximately two papers per lecture
Read them before class
Post thoughts to wiki
Introduction
Content and Applications
Transit Networks
Cellular & Mobile Networks
Access Networks

26. High-Level Course Structure
Reading and analyzing research papers
Different ways to approach management problems
Summaries, critiques, and comparisons of the papers
Lectures and Discussion
Overview of background material
Discussion and debate about the research papers (old school vs. new school)
Problem Sets
Learning the platforms for evaluating your ideas
Click/Emulab, OpenFlow/NOX, and measurements
Final research project
Novel research with a system-building component

27. Configuration Configuration defines the network’s behavior Problem
Network configuration is low-level, vendor-specific, and error-prone
Network configuration is a significant cause of downtime
Solutions
Design tools that make the network easier to manage
Refactor network design to make networks more manageable

28. Traffic Engineering
Network operators must manage network capacity, performance, and cost
Problems
Traffic is dynamic (network conditions are, too)
Determining the outcome of a configuration change is challenging
Solutions
Offline tuning of configuration parameters
Online adaptation of configuration, paths, etc.

29. Troubleshooting
Identifying the source of a problem is difficult enough…
Let alone determining how to fix it!
Monitor x y
Targets
Better example here? Why High? Google stuff?
Combination of active and passive measurements
Inference tools, data mining, etc.
Open question: Can better architectures make troubleshooting easier?

30. Security
The network is ripe for attackers who seek monetary gain, destruction, etc.
Problems
Spam is 95% of all traffic
30,000+ phishing attacks every month …
Solutions
Analyze network traffic data and design better detection
Redesign the network to make these attacks more difficult to mount in the first place

31. Maintenance and Planning
Operators must maintain high availability in the face of failures and planned maintenance
Problems
Network failures can disrupt connectivity
Network resources must be reprovisioned as demands increase, etc.
Solutions
Routing protocols for “hitless” planned maintenance
Better cost models
Arbor networks study

32. Frequently Changing Configuration Commands
Other “Hot Topics”
Frequently Changing Configuration Commands
Programmable Hardware
Configuration Languages
Home Networking and Access Network Performance

33. Class Components and Grading
Problem sets and Labs (45%)
Hands on
First assignment will be out this week
Two Quizzes (25%)
October 20 and December 1
Covering papers and lecture material
Project (30%)
Research project idea of your choosing
Should apply ideas from the class
Groups of 3-5 people
Will be adding project ideas to wiki soon

34. More Logistics…

35. Lateness
Late policy: Maximum of 72 hours late throughout the term (use as you like).
All problem sets and projects will be due at 11:59 p.m. on the due date.
All problem sets and projects will be turned in on T-Square.

36. Collaboration Policy See the Georgia Tech Honor Code
Sign up in groups of five to work on problem sets and projects. Use the wiki to declare your groups
Working together on assignments is encouraged, but you must
turn in your own assignments
write your own code, analysis
acknowledge your collaborators

37. How to Read

38. You Spend a Lot of Time Reading
Reading papers for grad classes (like this one!)
Reviewing papers for conferences/journals
Giving colleagues feedback on their papers
Keeping up with work related to your research
Staying broadly educated about the field
Transitioning into a new research area
Learning how to write better papers 
So, it is worthwhile to learn to read effectively

39. Why Read Research Papers?
Read for a conference or a class
Keep current in your own field
Get “up to speed” in a new field
Learn about a sub-field (e.g., wireless)
Learn about another discipline that may offer solutions to a problem

40. Step 1: Deciding What to Read
Purpose: Learn about “hot topics” of current research in an area. (searching for problems, etc.)
Approach: Scan papers in latest conference proceedings
Purpose: Get up to speed on sub-field
Approach: Transitive closure of related work of papers in a top conference
Purpose: Learn about an area that is further afield
Approach: Ask expert colleagues

41. Step 2: Deciding How to Read
Always “top down”
First: Abstract, introduction, conclusion
Rest of paper if necessary
If you want to do follow-up research
If you want to better understand the methods/conclusions
Next steps depend on specific purpose

42. Reading the News Conference proceedings Top-Down Method
Goal: Grasp main idea of a collection of a large number of papers. Keep informed about problems and recent solutions
Top-Down Method
Skim table of contents: Papers are clustered into “sessions” which typically identify the main areas
Consider authors
Prioritize by (1) area of interest (2) reputable authors

43. How to Conduct a Literature Survey
Create the seed
Recent paper from top conference
Survey paper, if one exists
Seminal paper, if it is different from the above
Perform transitive closure of cited work
Read related work sections of above papers

44. Keeping Notes
One-sentence summaries are infinitely better than nothing at all
Primitive approach: Single file of notes
Better: Database with BibTeX
There are some existing tools for bibliography management
Will also help you more quickly construct related work sections for your papers

45. Keshav’s Three-Pass Approach: Step 1
A ten-minute scan to get the general idea
Title, abstract, and introduction
Section and subsection titles
Conclusion
Bibliography
What to learn: the five C’s
Category: What type of paper is it?
Context: What body of work does it relate to?
Correctness: Do the assumptions seem valid?
Contributions: What are the main research contributions?
Clarity: Is the paper well-written?
Decide whether to read further…
Keep this in mind when you write your papers, so the readers (and reviewers) decide to read further… 

46. Keshav’s Three-Pass Approach: Step 2
A more careful, one-hour reading
Read with greater care, but ignore details like proofs
Figures, diagrams, and illustrations
Mark relevant references for later reading
Grasp the content of the paper
Be able to summarize the main thrust to others
Identify whether you can (or should) fully understand
Decide whether to
Abandon reading the paper in any greater depth
Read background material before proceeding further
Persevere and continue on to the third pass

47. Keshav’s Three-Pass Approach: Step 3
Several-hour virtual re-implementation of the work
Making the same assumptions, recreate the work
Identify the paper’s innovations and its failings
Identify and challenge every assumption
Think how you would present the ideas yourself
Jot down ideas for future work
When should you read this carefully?
Reviewing for a conference or journal
Giving colleagues feedback on a paper
Understanding a paper closely related to your research
Deeply understanding a classic paper in the field

48. Other Tips for Reading Papers
Read at the right level for what you need
“Work smarter, not harder”
Read at the right time of day
When you are fresh, not sleepy
Read in the right place
Where you are not distracted, and have enough time
Read actively
With a purpose (what is your goal?)
With a pen or computer to take notes
Read critically
Think, question, challenge, critique, …

49. How to Read For This Class
Read critically
Questions:
Is the question important?
Does this system make the right “division of labor”?
Is the placement of function appropriate?
Are there other disciplines that can be brought to bear on this problem?
Does the system design (or approach) make sense?

50. Next Three Classes: Crash Review
The Host
Discovery: DNS, ARP, lookup, interconnection, naming and addressing
Resource sharing: TCP
The Data Plane
Router internals: Scheduling, forwarding, packet classification, etc.
Forwarding tables, lookup, etc.
The Control Plane
Spanning tree protocols, routing protocols (intradomain, interdomain, etc.)