1 / 52

Networks and distributed systems

Networks and distributed systems. Lec 1: Evolution of the Internet. Jinyang Li Jinyang@cs.nyu.edu. Know your staff. Instructor: prof. Jinyang Li jinyang@cs.nyu.edu Office Hour: Wed 5-6pm (715 Broadway Rm 705) Class webpage http://www.news.cs.nyu.edu/classes/fa07

fola
Download Presentation

Networks and distributed systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Networks and distributed systems Lec 1:Evolution of the Internet Jinyang Li Jinyang@cs.nyu.edu Networks and distributed systems

  2. Know your staff • Instructor: prof. Jinyang Li • jinyang@cs.nyu.edu • Office Hour: Wed 5-6pm (715 Broadway Rm 705) • Class webpage http://www.news.cs.nyu.edu/classes/fa07 • Register for class mailing list Networks and distributed systems

  3. The course will teach you … • to appreciate design principles of the Internet • How it works and why it works • to address new networking challenges • How to do independent research Networks and distributed systems

  4. Who should take this class? • Core grad-level class • Satisfy M.S. requirement of a “project” class • Satisfy Ph.D. breadth requirement • Pre-requisite: • Basic knowledge on networks • Programming experience • Useful books: • Computer networks (Peterson & Davie) • TCP/IP illustrated (Stevens) Networks and distributed systems

  5. Class material • Lectures/readings • Read assigned research papers before class • Participate in class discussion • Assignments • Solve concrete problems, get your hands dirty! • Projects • Can you identify and tackle a challenge with guidance? Networks and distributed systems

  6. Grading • Participation 20% • two in-class mini-quiz on “readings du jour” • Two take home assignments 20% • Project 60% • Teams of 2-3 people • Starting new week • Bi-weekly meetings with me Networks and distributed systems

  7. Questions? • Sign up sheet Networks and distributed systems

  8. A brief history of communication • Telephone networks • Dial to set up a path • Paths carry analog voice signals from one phone to another • Networking means building paths Networks and distributed systems

  9. Building paths  connecting wires Switchboard Operators 1960 Networks and distributed systems

  10. The quest for a survivable network • Sputnik --> ARPA --> survivable networks • Telephone network is not survivable • Destroy of a switching center is highly disruptive • Not possible to build reliable paths under attacks Networks and distributed systems

  11. pkt len Src Addr Dst addr header payload Packet switching • Baran & Davies (60s) • Packets are digital, self-contained, of limited size • Decentralized store and forward • Networking means delivering packets to endpoints Networks and distributed systems

  12. H2 H1 H2 H1 An example of packet switching H2 H1:P4 H2:P1 H3:P2 1 2 4 3 H1 H3 2 1 3 H1:P1 H2:P2 H3:P3 Networks and distributed systems

  13. ARPANET Networks and distributed systems

  14. Internet: Connecting many networks • Many packet switching networks • ARPANET, Packet radio, SATnet • Goal: make networks work together! • Solution: TCP/IP Kahn &Cerf Networks and distributed systems

  15. Alternative #1: single technology, single network • Render existing networks/apps useless • Does not accommodate new technology • Hard for decentralized control • (early phone network is like this) Networks and distributed systems

  16. Alternative #2: Translation Gateway H1: ABCD H2: 计算机 • Translation is hard • different features/headers, N^2 combinations! • How to translate addresses? Translation gateway Networks and distributed systems

  17. H1,H2’s IP addr H2, GW’s low-level addr H1, GW’s low-level addr 3. Internet wins H2: 128.122.108.71 H1: 18.26.4.9 • IP over everything • A uniform header / addressing format IP router Networks and distributed systems

  18. Internet design challenges • How to address networks and hosts? • Address size? Resolve IP addr to subnet addr? • How to compute route and forward packets? • How to reliably deliver packets? • Error recovery • Flow control • How to cope with different max packet size? Networks and distributed systems

  19. Addressing scheme • Early 80s: • 32-bit globally unique IP address • 8 bit net number, 24 bit host number • Embed subnet address to low 24 bit • Now: 32-bit • Variable length net number (CIDR) • Address resolution protocol (ARP) to obtain • subnet addr (MAC addr) from IP Networks and distributed systems

  20. Routing • Early 80s: • 256-entry routing table, indexed by top 8 bits of addr • Static default g/w • Now: • Intra-domain routing: OSPF, RIP • Inter-domain routing: BGP • approx. 250,000 BPG entries now Networks and distributed systems

  21. Reliable delivery • Early 80s • IP is best-effort only • TCP ran at end hosts for error/flow control • Now: • IP is best effort only • TCP is separated from IP • TCP performs both error and congestion control Networks and distributed systems

  22. Packet size policy • Early 80s: • Senders only know local net’s MTU • G/Ws fragment large packets into smaller MTUS • End hosts reassembles fragments • Now: same. :-) Networks and distributed systems

  23. “Internet” demo 1977 ARPANET PRnet SateNET Networks and distributed systems

  24. Internet map 1987 Networks and distributed systems

  25. Why TCP/IP wins? • Universal • IP-over-everything • Best effort only • End-to-end design • Robust • Soft-state only inside network • Fate sharing • Be liberal in what you accept; be conservative in what you send Networks and distributed systems

  26. Internet’s growing stage • 1978 TCP/IP split • 1984 Domain name system • 1986 Incorporating congestion control in TCP • 1990 ARPANET disappears, first ISP is born • Nodes double every year…. Networks and distributed systems

  27. The revolution, good and bad • Email 1971 • Apple II 1977, IBM PC 1981 • Web 1990 • VoIP, File sharing, Video streaming, Web 2.0 • Worms 1988, viruses • DoS attacks • Spam Networks and distributed systems

  28. Internet design goals • Interconnect different networks • Packet switching • Uniform addressing and IP header • Robust • Route packets instead of building path • Network is state-less, forwards packets based on addr • Flexible • IP is best effort only • Separate TCP from IP Networks and distributed systems

  29. The more problematic goals 4. Decentralization • Routing across multiple admin domains is still error-prone 5. Cheap and easy to attach new nodes • Cumbersome to attach new devices, move existing ones around 6. Accountability Networks and distributed systems

  30. Internet weaknesses • Assumes trusted participants • Assumes non-greedy sources • Security • Hard to incrementally deploy new protocols Networks and distributed systems

  31. New challenges Networks and distributed systems

  32. New types of networks: wireless • 2007 MIT Cartel Networks and distributed systems

  33. New networks: wireless mesh Networks and distributed systems

  34. New networks: sensor Networks and distributed systems

  35. New services • What’s the next killer app? Networks and distributed systems

  36. Battling existing woes Networks and distributed systems

  37. Battling existing woes Networks and distributed systems

  38. Course Syllabus • Core networking concepts • Naming and addressing • Routing • Managing shared resources • Wireless • Network services • Security Networks and distributed systems

  39. Part I: Core networking concepts Reliable transport Networks and distributed systems

  40. Coping with best-effort • Why don’t applications use IP directly? • IP is a host-to-host protocol • Many applications want reliable, in-order delivery Networks and distributed systems

  41. sshd browser ssh apache write read TCP software architecture User-space User-space kernel kernel Networks and distributed systems

  42. Coping with best-effort • Challenges for a reliable transport protocol • Loss • Variable delays • Packet reordering • Duplicate packets Networks and distributed systems

  43. Src port Dst port Seq # Ack # flags window cksum Data: 1:1460 1461:1700 1701:1999 2000:2500 2501:2800 1701 Ack: 1701 1461 1701 TCP overview • Provides in-order, reliable, duplex byte-streams • Uses cumulative ACKs Networks and distributed systems

  44. Reliability via retransmission • How does TCP know when to re-transmit? • Timer driven • No ACKs for a while… • Data driven • Many duplicate ACKs Networks and distributed systems

  45. Timer-driven retransmission • What is the ideal time to retransmit? • What if we literally use RTT as timeout? Networks and distributed systems

  46. Timer-driven retransmission • Calculate running average of RTT • EWMA: srtt =  * r + (1 - ) * srtt • Set timeout (RTO) • Used to use RTO = 2 * srtt • Now: RTO = srtt + 4 * rttdev rttdev =  * |r-srtt| + (1- ) * rttdev Networks and distributed systems

  47. An example RTT distribution Avg: 99.2ms Std: 1.4ms Networks and distributed systems

  48. TCP timers • What if a retransmission times out? • Exponential back off • TCP timeouts are extremely conservative • Granularity of 500ms or 200ms Networks and distributed systems

  49. Data: 1:1460 1461:1700 1701:1999 2000:2500 2501:2800 1701 Ack: 1701 1461 1701 Fast retransmit • If a segment is lost, duplicate ACKs result • TCP retransmit upon seeing 3 duplicate ACKs Networks and distributed systems

  50. Fast retransmit • What would trick fast retransmit into spurious retransmission? • When would fast retransmit fail to avoid timeout? • Loss of a re-sent packet • Multiple losses in a window Networks and distributed systems

More Related