1. October 16, 2002 1 The Future of Broadband Wireless (and the role of “awareness” in wireless Internet performance) Carey Williamson iCORE Professor Department of Computer Science University of Calgary

2. October 16, 2002 2 Introduction r It is an exciting time to be an Internet researcher (or even a user!) r The last 10 years of Internet development have brought many advances: m World Wide Web (WWW) m Media streaming applications m “Wi-Fi” wireless LANs m Mobile computing m E-Commerce, mobile commerce m Pervasive/ubiquitous computing

3. October 16, 2002 3

4. 4 The Wireless Web r The emergence and convergence of these technologies enable the “wireless Web” m the wireless classroom m the wireless workplace m the wireless home r Holy grail: “anything, anytime, anywhere” access to information (when we want it, of course!) r My iCORE mandate: design, build, test, and evaluate wireless Web infrastructures

5. October 16, 2002 5 Clarification “Wireless Communications” “Wireless Internet” = (the enabler) (the value-added service)

6. October 16, 2002 6 Internet Protocol Stack r Application: supporting network applications and end-user services m FTP, SMTP, HTTP, DNS, NTP r Transport: end to end data transfer m TCP, UDP r Network: routing of datagrams from source to destination m IPv4, IPv6, BGP, RIP, routing protocols r Data Link: hop by hop frames, channel access, flow/error control m PPP, Ethernet, IEEE 802.11b r Physical: raw transmission of bits Application Transport Network Data Link Physical 001101011...

7. October 16, 2002 7 Pieces of the Puzzle r Portable computing devices: no problem (cell phones, PDAs, notebooks, laptops…) r Wireless access: not much of a problem (BlueTooth, IEEE 802.11, 802.11b, “WiFi”, 802.11a, Pringles…) r Security: still an issue, but being addressed r Services: the next big growth area??? r Performance transparency: providing an end-user experience that is hopefully no worse than that in traditional wired Internet desktop environments (my focus)

8. October 16, 2002 8 Research Theme r Existing layered Internet protocol stack does not lend itself well to providing optimal performance for diversity of service demands and environments r Who should bend: users or protocols? r Explore the role of “awareness” in Internet protocol performance r Identify tradeoffs, evaluate performance

9. October 16, 2002 9 Talk Overview r Introduction r Background m Emerging Wireless Trends and Technologies m The Future of Broadband Wireless r The Role of “Awareness” m TCP 101 m Motivating Examples m Our Work on CATNIP r Concluding Remarks

10. October 16, 2002 10 Brief History: Cellular/Wireless r First Generation (1G): analog (cellular voice, AMPS, RTMS, TACS, 1980’s) r Second Generation (2G): digital (IS-64, GSM, ISM-95, 8-32 kbps, 1990’s) r Third Generation (3G): broadband multimedia (always on, UMTS, 334 kbps-2 Mbps, 2000’s) 2.5G You are here

11. October 16, 2002 11 Some Interesting Reading r Brave New Unwired World (BNUW), by Alex Lightman and William Rojas r In a nutshell, the authors argue that: m 2.5G is dead m 3G is a waste of time (and money) m 4G is EVERYTHING!!!

12. October 16, 2002 12 Another Lightman Opinion r “the success of a technology in the marketplace is inversely proportional to the amount of hype associated with that technology prior to its release” Examples : ISDN BlueTooth 3G Examples : Internet, Web, napster, WiFi

13. October 16, 2002 13 What is 4G then? r Culmination of wireless Internet revolution r Convergence of key emerging technologies: IP-based Networks Satellite Wireless Services Semiconductors Microprocessors WIDs New Interfaces Wearable Computers NanoTech Molecular Engineering Backhaul NWs RF elements Storage technology Image Generation Quantum Antenna Arrays GPS 802.11b

14. October 16, 2002 14 Some Challenges/Opportunities r Ultra low-power processors: m pg 108: “could change the entire industry…” r Services: m pg 76: “extension of the Internet to mobile devices…whole new range of Internet services…personalized, location-sensitive content…previously impossible or impractical” r Awareness: m pg 221: “Location/context-aware applications… can determine and react to current physical computing context of mobile users… altering information presented to users accordingly”

15. October 16, 2002 15 The Future? r Service-centric economy r Significant shifting of economic power r The “winner” is likely to be either Japan (iMODE, DoCoMo) or China (Internet growth, wireless growth) r Reasons: m cooperation, encouragement, support from government on a national scale m strategic alliances within and across industries

16. October 16, 2002 16 Talk Overview r Introduction r Background m Emerging Wireless Trends and Technologies m The Future of Broadband Wireless r The Role of “Awareness” m TCP 101 m Motivating Examples m Our Work on CATNIP r Concluding Remarks

17. October 16, 2002 17 My iCORE Research Team r Martin Arlitt: Web performance, workload characterization r Qian Wu: TCP, ns-2 simulation r Guangwei Bai: network traffic measurement and modeling r Tianbo Kuang: wireless measurements, video compression, streaming media r Nayden Markatchev: technical support r Grad Students: Mingwei Gong, Yujian Li, Kehinde Oladosu, Fang Xiao, Andreas Hirt, Abhinav Gupta, Gwen Houtzager Application Transport Network Data Link Physical

18. October 16, 2002 18 Internet Protocol Stack r Application: supporting network applications and end-user services m FTP, SMTP, HTTP, DNS, NTP r Transport: end to end data transfer m TCP, UDP r Network: routing of datagrams from source to destination m IPv4, IPv6, BGP, RIP, routing protocols r Data Link: hop by hop frames, channel access, flow/error control m PPP, Ethernet, IEEE 802.11b r Physical: raw transmission of bits Application Transport Network Data Link Physical 001101011...

19. October 16, 2002 19 Viewpoint r “Layered design is good; layered implementation is bad” -Anon. r Good: m unifying framework for describing protocols m modularity, black-boxes, “plug and play” functionality, well-defined interfaces (good SE) r Bad: m increases overhead (interface boundaries) m compromises performance (ignorance)

20. October 16, 2002 20 Research Theme r Existing layered Internet protocol stack does not lend itself well to providing optimal performance for diversity of service demands and environments r Who should bend: users or protocols? r Explore the role of “awareness” in Internet protocol performance r Identify tradeoffs, evaluate performance

21. October 16, 2002 21 Tutorial: TCP 101 r The Transmission Control Protocol (TCP) is the protocol that sends your data reliably r Used for email, Web, ftp, telnet, … r Makes sure that data is received correctly: right data, right order, exactly once r Detects and recovers from any problems that occur at the IP network layer r Mechanisms for reliable data transfer: sequence numbers, acknowledgements, timers, retransmissions, flow control...

22. October 16, 2002 22 TCP 101 (Cont’d) r TCP is a connection-oriented protocol SYN SYN/ACK ACK GET URL YOUR DATA HERE FIN FIN/ACK ACK

23. October 16, 2002 23 TCP 101 (Cont’d) r TCP slow-start and congestion avoidance ACK

24. October 16, 2002 24 TCP 101 (Cont’d) r TCP slow-start and congestion avoidance ACK

25. October 16, 2002 25 TCP 101 (Cont’d) r TCP slow-start and congestion avoidance ACK

26. October 16, 2002 26 TCP 101 (Cont’d) r This (exponential growth) “slow start” process continues until either of the following happens: m packet loss: after a brief recovery phase, you enter a (linear growth) “congestion avoidance” phase based on slow-start threshold found m all done: terminate connection and go home

27. October 16, 2002 27 Simple Observation r Consider a big file transfer download: m brief startup period to estimate network bandwidth; most time spent sending data at the “right rate”; small added penalty for lost packet(s) r Consider a typical Web document transfer: m median size about 6 KB, mean about 10 KB m most time is spent in startup period; as soon as you find out the network capacity, you’re done! m if you lose a packet or two, it hurts a lot!!!

28. October 16, 2002 28 The Problem (Restated) r TCP doesn’t realize this dichotomy between optimizing throughput (the classic file transfer model) versus optimizing transfer time (the Web document download model) r Wouldn’t it be nice if it did? (i.e., how much data it was sending, and over what type of network) r Some research starting to explore this...

29. October 16, 2002 29 Motivating Example #1 r Wireless TCP Performance Problems Wired Internet Wireless Access High capacity, low error rate Low capacity, high error rate

30. October 16, 2002 30 Motivating Example #1 r Solution: “wireless-aware TCP” (I-TCP, ProxyTCP, Snoop-TCP,...)

31. October 16, 2002 31 Motivating Example #2 r Multi-hop “ad hoc” networking Carey Janelle

32. October 16, 2002 32 Motivating Example #2 r Multi-hop “ad hoc” networking Carey Janelle Yannis

33. October 16, 2002 33 Motivating Example #2 r Multi-hop “ad hoc” networking Carey Janelle Yannis

34. October 16, 2002 34 Motivating Example #2 r Multi-hop “ad hoc” networking Carey Janelle Yannis

35. October 16, 2002 35 Motivating Example #2 r Two interesting subproblems: m Dynamic ad hoc routing: node movement can disrupt the IP routing path at any time, disrupting TCP connection; yet another way to lose packets!!!; possible solution: Explicit Loss Notification (ELN) m TCP flow control: the bursty nature of TCP packet transmissions can create contention for the shared wireless channel among forwarding nodes; possible solution: rate-based flow control

36. October 16, 2002 36 Example of Our Work r Context-Aware Transport/Network Internet Protocol (CATNIP) r Motivation: “Like kittens, TCP connections are born with their eyes shut” - CLW 2002 r Research Question: How much better could TCP perform if it knew what it was trying to accomplish (e.g., Web document transfer)?

37. October 16, 2002 37 Some Key Observations (I think) r Not all packet losses are created equal r TCP sources have relatively little control r IP routers have all the power!!!

38. October 16, 2002 38 Tutorial: TCP 201 r There is a beautiful way to plot and visualize the dynamics of TCP behaviour r Called a “TCP Sequence Number Plot” r Plot packet events (data and acks) as points in 2-D space, with time on the horizontal axis, and sequence number on the vertical axis

39. October 16, 2002 39 Time SeqNum X + Key: X Data Packet + Ack Packet X X X X X X X X X X X X X + + + + + + + + + + + + +

40. October 16, 2002 40 TCP 201 (Cont’d) r What happens when a packet loss occurs? r Quiz Time... m Consider a 14-packet Web document m For simplicity, consider only a single packet loss

41. October 16, 2002 41 Time SeqNum X + Key: X Data Packet + Ack Packet X X X X X X X X X X X X + + + + + + + + + + + + ?

42. October 16, 2002 42 Time SeqNum X + Key: X Data Packet + Ack Packet X X X X X X X X X X X X + + + + + + + + + + + + X +

43. October 16, 2002 43 Time SeqNum X + Key: X Data Packet + Ack Packet X X X X X X X X X X X X + + + + + + + + + ?

44. October 16, 2002 44 Time SeqNum X + Key: X Data Packet + Ack Packet X X X X X X X X X X X X + + + + + + + ++++ + X +

45. October 16, 2002 45 Time SeqNum X + Key: X Data Packet + Ack Packet X + ?

46. October 16, 2002 46 Time SeqNum X + Key: X Data Packet + Ack Packet X X X + + + X X X X + + + + X X X + + +

47. October 16, 2002 47 TCP 201 (Cont’d) r Main observation: m “Not all packet losses are created equal” r Losses early in the transfer have a huge adverse impact on the transfer latency r Losses near the end of the transfer always cost at least a retransmit timeout r Losses in the middle may or may not hurt, depending on congestion window size at the time of the loss

48. October 16, 2002 48 The TCP Transfer “Pain Profile” SeqNum of the Single Lost Packet 1 N Relative Transfer Time

49. October 16, 2002 49 Design of CATNIP Can we make the TCP/IP protocols “smarter” about the specific job they are trying to do?  Yes. Convey application-layer context information to the TCP and IP layers Network Transport Application Document Size Packet Priority

50. October 16, 2002 50 Design of CATNIP (Cont’d) Q: What could a TCP source do differently? A: If it knew how much data it had to send, and how far along it was already, then maybe…  Rate-Based Pacing of the Last Window (RBPLW)  Early Congestion Avoidance (ECA)  Selective Packet Marking (SPM): Use the reserved high-order bit in the TCP header to convey packet priority information (high priority for the really crucial packets)

51. October 16, 2002 51 Design of CATNIP (Cont’d) Q: What could an IP router do differently? A: If it knew which packets were the “painful” ones to lose, then the router could…  CATNIP-Good: give them preferential treatment, and avoid throwing them away (if possible) when congested  CATNIP-Bad: throw them away

52. October 16, 2002 52 Simulation Evaluation Network model: Client 100 Server 1 Server 2 Server 10 Client 1 Client 2 Client 99 1.5 Mbps, 5 ms 10 Mbps, 5 ms RouterSRouterC

53. October 16, 2002 53 Simulation Evaluation (Cont’d) Web workload model:  100 clients, 10 different Web pages  Use empirically-observed distribution to determine the size, and the number of embedded images

54. October 16, 2002 54 Simulation Evaluation (Cont’d) Factors and Levels: Performance metrics:  transfer time for each Web page  packet loss ratio

55. October 16, 2002 55 Simulation Results for DropTail Routers Reno/ RBPLW Reno ECA ECA/RBPLW Mean and Standard Deviation of Transfer Times

56. October 16, 2002 56 Simulation Results for CATNIP-Good Routers Mean and Standard Deviation of Transfer Times Reno/DropTail SPM/Good

57. October 16, 2002 57 Observations r Sources have relatively little control r IP routers have all the power r Adding context-awareness at the IP routers improves both mean and standard deviation of Web page transfer times r SPM and CATNIP-Good provide most of the benefit r Advantages of CATNIP are most prominent at low levels of IP packet loss (1-5%)

58. October 16, 2002 58 Summary r There seem to be performance advantages to bending the rules regarding the Internet protocol stack layered model r The general notion of “awareness” needs to explored in a variety of contexts m wireless networks, ad hoc routing, TCP/IP, Web caching, mobile computing, adaptive applications, … r Many exciting issues to explore!!

59. October 16, 2002 59 The Next Steps r Putting it all together: Web + Wireless r Wireless Internet Performance Lab (UofC) r Experimental Laboratory for Internet Systems and Applications (UofS/UofC,CFI) r Research Collaborations: m UofC, UofS, UofA, TRLabs, CS/ECE m Nortel? HP? Cisco? Agilent? Telus Mobility?

60. October 16, 2002 60 The End: Question Time! r For more information: m Email: carey@cpsc.ucalgary.ca m URL: www.cpsc.ucalgary.ca/~carey r Many thanks to my research team and the TeleSim Research Group at the U of C r Special thanks to iCORE, NSERC, CFI, andTelus Mobility