1. COMP 562: “Advanced Topics in Networking” Qian Zhang Spring 2009 HKUST Introduction 1-1

2. Course Info  Instructor: Qian Zhang www.cs.ust.hk/~qianzh  Course web site http://www.cs.ust.hk/~qianzh/comp562- 2009/comp562-index.htm http://www.cs.ust.hk/~qianzh/comp562- 2009/comp562-index.htm contains all notes, announcements, etc. Check it regularly!  Lecture schedule  Tuesday/Thursday 12:00-13:20 Rm 2463 Introduction 1-2

3. Course Info  Textbook: James Kurose and Keith Ross  Computer Networking: A Top Down Approach, 4 th ed. Addison Wesley, 2007  http://wps.aw.com/aw_kurose_network_4/ with useful resource material http://wps.aw.com/aw_kurose_network_4/  The reading materials online for paper reading and reviewing  Experience networking research through team projects (1-2 students)  Understand what is good research  Hands-on experience in networking research  Appreciate team work / collaborations  Survey oriented (own idea is encouraged) Introduction 1-3

4. Course Info  Grading scheme  Homework (2) 30 points  Paper presentation (1) 15 points  Project report (1) 15 points  Final Exam 40 points  Paper presentation  Everyone reviews and presents 1 paper  Email me ids of 3 papers that you’d like to present by Feb. 27  Present the paper and give your own comments on the selected paper Introduction 1-4

5. More about Class Project  Can be individual project or group project (at most 2 in a group)  Two types I can see:  Survey a problem in depth (read several papers related to the problem and summarized/ discuss)  Do some research on a given problem  Sample project topics:  Most commercial systems (e.g. PPlive) are not based on open source. Try to deduce the algorithm for specific p2p streaming applications Introduction 1-5

6. Course Schedule  Review of the basic principles of computer networking  Broadcasting and Multicasting  Peer-to-Peer Networking  Wireless Networking  Multimedia Networking and Quality of Service Provision  Advanced Topics for Congestion Control  Network Security  Student presentation Introduction 1-6

7. Introduction 1-7 Chapter 1 Introduction Computer Networking: A Top Down Approach, 4 th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007. A note on the use of these ppt slides: The notes used in this course are substantially based on powerpoint slides developed and copyrighted by J.F. Kurose and K.W. Ross, 2007

8. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-8

9. What’s the Internet: “nuts and bolts” view  Millions of connected computing devices: hosts = end systems  Running network apps Introduction 1-9 Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular handheld wired links access points  Communication links  Fiber, copper, radio, satellite  Transmission rate = bandwidth  Routers: forward packets (chunks of data)

10. What’s the Internet: “nuts and bolts” view  Protocols control sending, receiving of msgs  E.g., TCP, IP, HTTP, Skype, Ethernet  Internet: “network of networks”  Loosely hierarchical  Public Internet versus private intranet  Internet standards  RFC: Request for comments  IETF: Internet Engineering Task Force Introduction 1-10 Home network Institutional network Mobile network Global ISP Regional ISP

11. What’s the Internet: A Service View  Communication infrastructure enables distributed applications:  Web, VoIP, email, games, e- commerce, file sharing  Communication services provided to apps:  Reliable data delivery from source to destination  “Best effort” (unreliable) data delivery Introduction 1-11

12. Chapter 1: Roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-12

13. A Closer Look at Network Structure:  Network edge: applications and hosts Introduction 1-13  Access networks, physical media: wired, wireless communication links  Network core:  Interconnected routers  Network of networks

14. The Network Edge:  End systems (hosts):  Run application programs  E.g. Web, email  At “edge of network” Introduction 1-14 client/server peer-peer  Client/server model  Client host requests, receives service from always-on server  E.g. Web browser/server; email client/server  Peer-peer model:  Minimal (or no) use of dedicated servers  E.g. Skype, BitTorrent

15. Network Edge: Reliable Data Transfer Service Goal: data transfer between end systems  Handshaking: setup (prepare for) data transfer ahead of time  Hello, hello back human protocol  Set up “state” in two communicating hosts  TCP - Transmission Control Protocol  Internet’s reliable data transfer service TCP service [RFC 793]  Reliable, in-order byte- stream data transfer  Loss: acknowledgements and retransmissions  Flow control:  Sender won’t overwhelm receiver  Congestion control:  Senders “slow down sending rate” when network congested Introduction 1-15

16. Network Edge: Best Effort (Unreliable) Data Transfer Service Goal: data transfer between end systems  same as before!  UDP - User Datagram Protocol [RFC 768]:  Connectionless  Unreliable data transfer  No flow control  No congestion control App’s using TCP:  HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP:  streaming media, teleconferencing, DNS, Internet telephony Introduction 1-16

17. Access Networks and Physical Media Q: How to connect end systems to edge router?  Residential access nets  Institutional access networks (school, company)  Mobile access networks Keep in mind:  Bandwidth (bits per second) of access network?  Shared or dedicated? Introduction 1-17

18. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-18

19. The Network Core  Mesh of interconnected routers  The fundamental question: how is data transferred through net?  Circuit-switching: dedicated circuit per call: telephone net  Packet-switching: data sent thru net in discrete “chunks” Introduction 1-19

20. Network Core: Circuit Switching End-end resources reserved for “call”  Link bandwidth, switch capacity  Dedicated resources: no sharing  Circuit-like (guaranteed) performance  Call setup required Introduction 1-20

21. Network Core: Circuit Switching Network resources (e.g., bandwidth) divided into “pieces”  Pieces allocated to calls  Resource piece idle if not used by owning call (no sharing) Introduction 1-21  Dividing link bandwidth into “pieces”  Frequency division  Time division

22. Network Core: Packet Switching Each end-end data stream divided into packets  User A, B packets share network resources  Each packet uses full link bandwidth  Resources used as needed Introduction 1-22 Resource contention:  Aggregate resource demand can exceed amount available  Congestion: packets queue, wait for link use  Store and forward: packets move one hop at a time  Node receives complete packet before forwarding Bandwidth division into “pieces” Dedicated allocation Resource reservation

23. Packet Switching: Statistical Multiplexing Sequence of A & B packets does not have fixed pattern, shared on demand  statistical multiplexing TDM: each host gets same slot in revolving TDM frame Introduction 1-23 A B C 100 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link

24. Packet Switching versus Circuit Switching  Great for bursty data  Resource sharing  Simpler, no call setup  Excessive congestion: packet delay and loss  Protocols needed for reliable data transfer, congestion control  Q: How to provide circuit-like behavior?  Bandwidth guarantees needed for audio/video apps  Still an unsolved problem Is packet switching a “slam dunk winner?” Introduction 1-24

25. Internet Structure: Network of Networks  Roughly hierarchical  At center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage  Treat each other as equals Introduction 1-25 Tier 1 ISP Tier-1 providers interconnect (peer) privately

26. Internet Structure: Network of Networks  “Tier-2” ISPs: smaller (often regional) ISPs  Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Introduction 1-26 Tier 1 ISP Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet  Tier-2 ISP is customer of tier-1 provider Tier-2 ISPs also peer privately with each other.

27. Internet Structure: Network of Networks  “Tier-3” ISPs and local ISPs  Last hop (“access”) network (closest to end systems) Introduction 1-27 Tier 1 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet

28. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-28

29. How do Loss and Delay Occur? Packets queue in router buffers  Packet arrival rate to link exceeds output link capacity  Packets queue, wait for turn Introduction 1-29 A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers

30. Four Sources of Packet Delay  1. Nodal processing:  Check bit errors  Determine output link Introduction 1-30  2. Queueing  Time waiting at output link for transmission  Depends on congestion level of router A B nodal processing queueing

31. Delay in Packet-Switched Networks 3. Transmission delay:  R=link bandwidth (bps)  L=packet length (bits)  Time to send bits into link = L/R 4. Propagation delay:  d = length of physical link  s = propagation speed in medium (~2x10 8 m/sec)  propagation delay = d/s Introduction 1-31 propagation transmission Note: s and R are very different quantities! A B nodal processing queueing

32. Nodal Delay  d proc = processing delay  Typically a few microsecs or less  d queue = queuing delay  Depends on congestion level in the router  d trans = transmission delay  = L/R, significant for low-speed links  d prop = propagation delay  A few microsecs to hundreds of msecs Introduction 1-32

33. Packet Loss  Queue (aka buffer) preceding link in buffer has finite capacity  Packet arriving to full queue dropped (aka lost)  Lost packet may be retransmitted by previous node, by source end system, or not at all Introduction 1-33 A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area)

34. Throughput  Throughput: rate (bits/time unit) at which bits transferred between sender/receiver  Instantaneous: rate at given point in time  Average: rate over long(er) period of time Introduction 1-34 server, with file of F bits to send to client link capacity R s bits/sec link capacity R c bits/sec pipe that can carry fluid at rate R s bits/sec) pipe that can carry fluid at rate R c bits/sec) server sends bits (fluid) into pipe

35. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-35

36. Internet Protocol Stack  Application: supporting network applications  FTP, SMTP, HTTP  Transport: process-process data transfer  TCP, UDP  Network: routing of datagrams from source to destination  IP, routing protocols  Link: data transfer between neighboring network elements  PPP, Ethernet  Physical: bits “on the wire” Introduction 1-36 application transport network link physical

37. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-37

38. Network Security  Attacks on Internet infrastructure:  Infecting/attacking hosts: malware, spyware, worms, unauthorized access (data stealing, user accounts)  Denial of service: deny access to resources (servers, link bandwidth)  Internet not originally designed with (much) security in mind  Original vision: “a group of mutually trusting users attached to a transparent network”  Internet protocol designers playing “catch-up”  Security considerations in all layers! Introduction 1-38

39. What Can Bad Guys Do: Malware?  Spyware:  Infection by downloading web page with spyware  Records keystrokes, web sites visited, upload info to collection site  Virus  Infection by receiving object (e.g., e-mail attachment), actively executing  Self-replicating: propagate itself to other hosts, users Introduction 1-39  Worm:  Infection by passively receiving object that gets itself executed  Self-replicating: propagates to other hosts, users Sapphire Worm: aggregate scans/sec in first 5 minutes of outbreak (CAIDA, UWisc data)

40. Denial of Service Attacks  Attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic Introduction 1-40 1. Select target 2. Break into hosts around the network (see malware) 3. Send packets toward target from compromised hosts target

41. Sniff, Modify, Delete Your Packets Packet sniffing:  Broadcast media (shared Ethernet, wireless)  Promiscuous network interface reads/records all packets (e.g., including passwords!) passing by Introduction 1-41 A B C src:B dest:A payload  Ethereal software used for end-of-chapter labs is a (free) packet-sniffer  More on modification, deletion later

42. Masquerade as you  IP spoofing: send packet with false source address Introduction 1-42 A B C src:B dest:A payload

43. Masquerade as you  IP spoofing: send packet with false source address  Record-and-playback : sniff sensitive info (e.g., password), and use later  Password holder is that user from system point of view Introduction 1-43 A B C src:B dest:A user: B; password: foo

44. Masquerade as you  IP spoofing: send packet with false source address  Record-and-playback : sniff sensitive info (e.g., password), and use later  Password holder is that user from system point of view Introduction 1-44 A B later ….. C src:B dest:A user: B; password: foo

45. Introduction: Summary Covered a “ton” of material!  Internet overview  What’s a protocol?  Network edge, core, access network  Packet-switching versus circuit- switching  Internet structure  Performance: loss, delay, throughput  Layering, service models  Security Introduction 1-45