1. The Effect of First-Hop Wireless Bandwidth Allocation on End-to-End Network Performance Lili Qiu, Paramvir Bahl, Atul Adya Microsoft Research NOSSDAV’2002 Miami Beach, Florida

2. 2 Outline Motivate the problem First hop wireless bandwidth reservation schemes Performance evaluation Related work Conclusion

3. 3 Introduction IP telephony is becoming popular With the growth of wireless technologies, an IP- based portable phone is a compelling device for voice communication

4. Kyocera QCP 6035 (CDMA) - Palm 3.5 OSPalm 3.5 OS Nokia 9110 (GSM) - GEOS OSGEOS OS MS SmartPhone - WinCE 3.0 OS AudioVox Thera (CDMA2000) - PPC 2002 OSPPC 2002 OS Samsung I300 - Palm OSPalm OS Siemens SX 45 (GPRS) - PPC 2002 OSPPC 2002 OS Handspring Treo 180 - Palm OS (GSM)Palm OS (GSM) MSR’s UCoM (802.11) - PPC 2002PPC 2002 49 million PDA-Phones by the year 2007 [Cellular News 1/23/02]

5. 5 Research Issues Design space –Power –Security –Mobility –Bandwidth  this paper’s focus –… Wireless bandwidth management –Wireless technologies used in the first hop are still slow –Challenges End-to-end reservation is preferred for ensuring QoS Little QoS support in the Internet  reservation only at wireless hops Effectiveness of local reservation depends on location of bottleneck

6. 6 Motivation: Throughput of Internet Paths How often is a wireless application traversing the Internet rated-limited by its Internet path rather than wireless hop? Analyze the Internet tcpdump traces collected at microsoft.com –Incoming & outgoing web traffic, software download traffic, streaming media traffic DateTime# pkts# clients Dec. 20, 20006:53PM–9:01PM100 million134,475 Jan. 24, 200110:08AM -11:21AM20.4 million53,811

7. 7 Throughput of Internet Paths Different clients experience widely different throughput, from 1 Kbps to 10 Mbps Over 30% clients have throughput less than 20 Kbps  Internet path can become bottleneck Useful to consider congestion level of the Internet when making the bandwidth allocation decision in the first hop

8. 8 Temporal Stability of Internet Throughput Over 90% of the hosts have throughput variation within a factor of 2  Internet throughput is stable

9. 9 Our Approach Observation –Not efficient to reserve more bandwidth than what an application would use. –An application may use less BW either because it generates data at slower rate or because bottleneck is at other links (e.g. Internet). Approach –Passively monitor applications’ bandwidth –Adaptively modify allocated wireless bandwidth according to usage Places to deploy the technique –Infrastructure (Access point/Access server) –Client (PDA)

10. 10 First-hop Wireless Bandwidth Reservation Schemes 1.No reservation: best effort 2.R0: Reserve s 3.R1: Reserve min(s, f*I) 4.R2: Same as R1, except it periodically re-adjusts allocation s: the rate specified by the source I: Internet bandwidth f: tolerance factor to account for estimation error

11. 11 Performance Evaluation Simulations in ns-2 Senders use TFRC [FHP00] Compare the above four reservation schemes Three scenarios –Congestion at wireless hop –Congestion at the Internet path –Congestion at both places A B Senders Receivers 6Mbps Internet pathwireless hop

12. 12 Scenario 1: Congestion in the wireless hop First hop reservation maintains QoS when congestion occurs in the first hop. Simulation scenario: S = 48 Kbps I = 96 Kbps s: the rate specified by the source I: Internet bandwidth  Congestion in the wireless hop

13. 13 Scenario 2: Congestion in the Internet path R0 is wasteful. First hop reservation is ineffective when congestion occurs in the Internet. Simulation scenario: S = 48 Kbps, I = 24 Kbps  congestion in the Internet

14. 14 Scenario 3: Congestion at both Internet and wireless hop Reservation based on Internet throughput performs the best. S = 48 Kbps, I = 24 or 96 Kbps  congestion at both places

15. 15 Scenario 3: Congestion at both Internet and wireless hop (Cont.) Use the throughput in the Internet trace for our simulation –Pick hosts from the Dec. 2000 throughput trace, and assign their perceived throughput to the bandwidth of the Internet path –Vary the bandwidth of the links according to the trace Estimate throughput using past measurements Tolerance factor (f) = 1.5 Desired sending rate of a source –Either CBR: 16 Kbps, 24 Kbps, 32 Kbps, 48 Kbps –Or VBR: the rate of video traces we collected Poisson arrival & departure –mean duration = 8 minutes

16. 16 Scenario 3: Congestion at both Internet and wireless hop (Cont.) Allocating bandwidth that adapts to the Internet path’s throughput is even better.

17. 17 System Components Allocation Server monitors throughput and re-adjusts reservation periodically Access Server Polices users OptionAllocationAccessPro 1Client Easier to deploy 2AP No need for client cooperati on 3Gateway

18. 18 Related Work Studies on Internet path properties –Internet throughput remains stable on the time scales of minutes [BSSK97, ZDPS01] Admission controls –RSVP [ZDES+93] –Measurement-based admission control –Endpoint admission control [BKSS+00] Wireless QoS –IEEE 802.11e –Subnet bandwidth manager [RFC 2814]

19. 19 Conclusions Provide applications with better QoS without infrastructure support in the Internet Study several bandwidth allocation techniques for wireless hops Adaptive bandwidth allocation for first-hop wireless based on passive observation of Internet paths performs the best –Has better quality than no reservation –Admits more flows than naïve reservation Design choices Applications –Wireless real time applications

20. 20 Acknowledgement Venkata N. Padmanabhan Scott Hogan Rob Emanuel Chris Darling Al Lee