The Future of Broadband Wireless (and the role of “awareness” in wireless Internet performance)

1. The Future of Broadband Wireless(and the role of “awareness” inwireless Internet performance) Carey Williamson iCORE Professor Department of Computer Science University of Calgary

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

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

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

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

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

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

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

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

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

12. Another Lightman Opinion • “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: Internet, Web, napster, WiFi Examples: ISDN BlueTooth 3G

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

14. Some Challenges/Opportunities • Ultra low-power processors: • pg 108: “could change the entire industry…” • Services: • pg 76: “extension of the Internet to mobile devices…whole new range of Internet services…personalized, location-sensitive content…previously impossible or impractical” • Awareness: • 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. The Future? • Service-centric economy • Significant shifting of economic power • The “winner” is likely to be either Japan (iMODE, DoCoMo) or China (Internet growth, wireless growth) • Reasons: • cooperation, encouragement, support from government on a national scale • strategic alliances within and across industries

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

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

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

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

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

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

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

23. ACK TCP 101 (Cont’d) • TCP slow-start and congestion avoidance

24. ACK TCP 101 (Cont’d) • TCP slow-start and congestion avoidance

25. ACK TCP 101 (Cont’d) • TCP slow-start and congestion avoidance

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

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

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

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

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

31. Motivating Example #2 • Multi-hop “ad hoc” networking Janelle Carey

32. Motivating Example #2 • Multi-hop “ad hoc” networking Janelle Yannis Carey

33. Motivating Example #2 • Multi-hop “ad hoc” networking Janelle Yannis Carey

34. Motivating Example #2 • Multi-hop “ad hoc” networking Janelle Yannis Carey

35. Motivating Example #2 • Two interesting subproblems: • 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) • 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. Example of Our Work • Context-Aware Transport/Network Internet Protocol (CATNIP) • Motivation: “Like kittens, TCP connections are born with their eyes shut” - CLW 2002 • Research Question: How much better could TCP perform if it knew what it was trying to accomplish (e.g., Web document transfer)?

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

38. Tutorial: TCP 201 • There is a beautiful way to plot and visualize the dynamics of TCP behaviour • Called a “TCP Sequence Number Plot” • 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. + Key: X Data Packet + Ack Packet X + X + X + X + X SeqNum + X + X X + + X + X + X + X + X + X Time

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

41. ? Key: X Data Packet + Ack Packet + X + X + X + X SeqNum + X + X X + + X + X + X + X + X + X Time

42. + X Key: X Data Packet + Ack Packet + X + X + X + X SeqNum + X + X X + + X + X + X + X + X + X Time

43. Key: X Data Packet + Ack Packet X X X ? + X SeqNum + X + X X + + X + X + X + X + X + X Time

44. + Key: X Data Packet + Ack Packet X X X X + + + + X SeqNum + X + X X + + X + X + X + X + X + X Time

45. Key: X Data Packet + Ack Packet SeqNum ? + X + X Time

46. + X + X + X + X X + + X Key: X Data Packet + Ack Packet SeqNum + X X X + + + X + X Time

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

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

49. Document Size Packet Priority 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 Application Transport Network

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)