Course Overview and Introduction

1. Course Overview and Introduction CS 4251: Computer Networking IINick FeamsterSpring 2008

2. Goals • You have presumably already learned the basics, so we will focus on… • Depth • More in-depth treatment of various topics • Hands-on experience and skills • Testbeds: Emulab, PlanetLab, VINI • Tools: Scriptroute, Click, XORP • Analysis of real traces

3. Goals • Design Experience and Insights • `Internet was based on design priorities • Applications and requirements have changed • You will gain experience re-evaluating design decisions and changing protocols • Many recurring design “tricks” • Tree forming • Layering • Resource allocation and sharing • Naming

4. Logistics • Course Web page • http://www.gtnoise.net/classes/cs4251/fall_2008/ • Check this page regularly for updates to the syllabus, assignments, readings, etc. • Course mailing list • Sign up now/today if you are not already on it • http://www.gtnoise.net/mailman/listinfo/cs4251

5. Who Am I? • Nick Feamster • Assistant Professor • Networking: Operations and Security • Office: Klaus 3348 • Email address: on web page; use subject “CS 4251” • Office Hours: Wednesday, 2-3 p.m., by appt

6. Overview of Lectures • Holistic approach • Lectures organized by theme • Tree forming/path finding • Layering • Resource allocation and sharing • Naming • Textbook reading, research papers, “current events” • Read the readings before class! • Historically, many things covered in class that are not in texts

7. Lecture Structure: User-Generated • One strongly positive review of last year’s course: “just in time” topics • This year: Formalize this notion • Every Friday: Post a link to the course wiki (link soon) with a paper and one-line topic summary • Voting over weekend • Discuss paper in second half of Wednesday lecture • I will do this, too

8. Networking in Current Events Threats to the Internet’s naming system “Network Neutrality”

9. Other Things You’ll Learn • How does BitTorrent find your file? • How does the Georgia Tech wireless network allow you to “roam” across campus with the same IP address? • How do ISPs connect to one another? • Protocols, Economics, … • What could you do with two (or more) Internet connections at home?

10. Still More Things You’ll Learn • How many bits can you push over a physical channel? • How can you use encoding to increase this? • What’s inside a router? • Function, power issues, trends (e.g., programmability) • Performance guarantees (e.g., telephony, video)? • Can a network’s resources be subdivided?

11. Still More Things You’ll Learn • Are we running out of IP addresses? Who cares, and how can we combat this? • How do we reduce power utilization in data centers? • What are the bad guys doing? • Can we stop unwanted traffic? • How do we make it easier to run the network? • How do we make the network go faster? • Why is it so hard to figure out what’s wrong? • Social networks…?

12. Class Components and Grading • Problem sets (20%) • Paper and pencil • First assignment: September 3 • Hands-on Assignments (30%) • Experience with tools and traces • 2 Quizzes (25%) • Quiz: March 3 • Final: will set date soon (perhaps last week of class) • 1 Project (25%) • TBD. Work in groups. Programming/analysis/etc. • Most likely: Pict from a list, or propose your own • Late policy: Maximum of 72 hours late throughout the term

13. Collaboration Policy • See the Georgia Tech Honor Code • Working together on assignments is fine, but you must turn in your own assignments, and ultimately write your own code, analysis, etc.

14. Who are you? • Why are you taking this class? • What do you hope to learn? • (What have you learned already) • What do you want out of a class project? • Did you take 3251?

15. Overview of Course Content

16. Themes • Routing: Trees and Paths • The Protocol Stack: Protocols and Layering • Resource Allocation • Naming • Trust • Other themes • Hierarchy • Caching • Randomization

17. Georgia Tech The Internet: A Network of Networks Autonomous Systems (ASes) • Interconnected of the Internet Service Providers (ISPs) provide data communications services • Networks are connected using routers that support communication in a hierarchical fashion • Often need other special devices at the boundaries for security, accounting, … • Hosts and networks have to follow a common set of rules (protocols) Abilene Comcast AT&T Cogent

18. Challenges • Scale: 100,000,000s of hosts • Heterogeneity: • 25,000+ administrative domains (competing!) • Thousands of applications • Lots of users • Diversity of network technologies and media • Security:Adversarialenvironment

19. Trends and Open Problems • Reducing power consumption • E.g., in data centers • Making networks easier to manage • Improving trust/identity in networks • Spam, phishing attacks, etc. • Policy-related issues (net neutrality) • Programmability in routers/switches

20. Tree Forming and Route Finding

21. Computing Routes • To deal with large scale, Internet routing employs hierarchy • Internet Service Providers connect to one another with interdomainrouting protocols (BGP) • ISPs have business relationships with one another • ISPs have PoPs that are connected with intradomain routing protocols

22. 192.168.1.51 192.168.1.52 Gateways: Routers and Switches • Interconnect nodes to nodes • And networks to networks • No state about ongoing connections • Stateless packet switches • We can also think of your home router/NAT as performing the function of a gateway 68.211.6.120:50878 Home Network Internet 68.211.6.120:50879 (more on NATs in lecture 17)

23. Challenge: Scale

24. The Protocol Stack

25. Protocols: Interconnection • The syntax and semantics by which hosts and nodes agree on how to talk • Must be standardized and agreed upon by all parties • Standardization process • IETF Requests for Comments (RFC) • De-facto standards • Format of messages • Expectations for message delivery

26. Layering • Helps manage complexity • Each layer: • Relies on services from layer below • Provides services to layer above • For example: IP (network) layer • IP relies on connectivity to next hop, access to medium • IP provides a datagram service • Best effort delivery • Packets may be lost, corrupted, reordered, etc. • Layers on top of IP (e.g., TCP) may guarantee reliable, in-order delivery

27. Layering Mechanism: Encapsulation • This can be more complex • Example: Network layers can be encapsulated within another network layer User A User B Application(message)Transport(segment)Network(datagram)Link (frame) Get index.html Connection ID Source/Destination Link Address

28. email WWW phone... SMTP HTTP RTP... TCP UDP… IP ethernet PPP… CSMA async sonet... copper fiber radio... The Internet Protocol Stack • Need to interconnect many existing networks • Hide underlying technology from applications • Decisions • Network provides minimal functionality • IP as the “Narrow waist” Applications Technology

29. The “Narrow Waist” • Facilitates interconnection and interoperability • IP over anything, anything over IP • Has allowed for much innovation both above and below the IP layer of the stack • Any device with an IP stack can “get on the Internet” • Drawback: very difficult to make changes to IP

30. Resource Sharing

31. Resource Sharing • How? Multiplexing • Switched network • Party “A” gets resources sometimes • Party “B” gets them sometimes • Interior nodes (“Routers” or “Switches”) arbitrate access to resources

32. Circuit Switching • Resources are reserved • Source first establishes a connection (circuit) to the destination • Source sends the data over the circuit • Constant transmission rate • Example: telephone network • Early early versions: Human-mediated switches. • Early versions: End-to-end electrical connection • Today: Virtual circuits or lambda switching

33. Resource Sharing in Circuit-Switched Networks • Frequency-Division Multiplexing (FDM) • Link dedicates a frequency to each connection • Width of this frequency band is called “bandwidth” • We will discuss the capacity in Lecture 10 • Time-Division Multiplexing • Each circuit gets all of the bandwidth on a link for brief periods of time

34. Circuit Switching • Advantages • Fast and simple data transfer, once the circuit has been established • Predictable performance since the circuit provides isolation from other users • Guaranteed bandwidth • Disadvantages • What about bursty traffic? • Users with differing needs for bandwidth • What if all resources are allocated?

35. Packet Switching • Resources are not reserved • Packets are self-contained • Each has a destination address • Source may have to break up single message • Each packet travels independently to the destination host • Routers and switches use the address in the packet to determine how to forward the packets

36. Resource Sharing: Packet Switching • Statistical multiplexing • Switches arbitrate between inputs • Can send from any input that’s ready • Links are never idle when traffic to send • Efficiency! • Requires buffering/queues • Implies a service model/discipline (Lecture 21)

37. Delay in Packet Switched Networks • Four contributors to hop-by-hop delay • Processing: Lookup, etc. (Lectures 6 and 7) • Queueing: Time the packet must wait before being transmitted (Lecture 21) • Transmission: time to push the packet onto the link • Propagation: time for the packet to propagate from A to B • End-to-end performance metric: throughput • What (else) affects throughput

38. Forwarding: Packet-Switched Networks • Each packet contains a destination in the header • Much like a postal address on an envelope • Each hop (“router” or “switch”) inspects the destination address to determine the next hop • Will a packet always take the same path? • How do the hops know how to forward packets?