1. Bandwidth Allocation for Last Hop in Wireless Networks Universal Communicator Research

2. Introduction Goal –Improve QoS for wireless applications Challenges –Bottleneck may occur either at the Internet or at the wireless hop –Limited QoS support in the Internet

3. Universal Communicator Research Our Approach Observation –Not efficient to reserve more bandwidth than what an application would use. –An application may use less either because it generates data at slower rate or because bottleneck is at somewhere else (e.g. Internet). Approach –Passively monitor applications bandwidth usage –Adaptively allocate wireless bandwidth according to their usage Place to deploy the technique –Access point –Client

4. Universal Communicator Research Performance Evaluation Three scenarios –Congestion at wireless hop –Congestion at the Internet path –Congestion at both places Four approaches to compare –No reservation –R0: Reserve s –R1: Reserve min(s, f*I) –R2: Same as R1, except periodically re-adjusts allocation s: the rate specified by the source I: Internet bandwidth f: fudge factor to account for estimation error A B Senders Receivers 6Mbps Internet pathwireless hop

5. Universal Communicator Research Scenario 1: Congestion at the first wireless hop Reservation helps to improve QoS when congestion occurs at the portion of path where reservation takes effect. Simulation scenario: S = 48 Kbps I = 96 Kbps s: the rate specified by the source I: Internet bandwidth Congestion at the wireless hop

6. Universal Communicator Research Scenario 2: Congestion at the Internet path Reservation cannot help improve QoS when congestion occurs at the portion of the path which reservation has no control. Simulation scenario: S = 48 Kbps, I = 24 Kbps congestion at the Internet

7. Universal Communicator Research Scenario 3: Congestion at both Internet and wireless hop Reservation based on Internet throughput performs the best. S = 16, 24, 32, 48, 64 Kbps, I = 24 or 96 Kbps congestion at both places

8. Universal Communicator Research Scenario 3: Congestion at both Internet and wireless hop (Cont.) Allocate bandwidth that adapts to the Internet paths throughput further improves performance. S = 6 – 136 Kbps (including CBR and VBR) I is from real bandwidth trace collected from microsoft.com congestion at both places

9. Universal Communicator Research Conclusions Propose adaptive bandwidth allocation for last wireless hop based on passive observation of Internet paths The proposed approach out-perform existing ones –Has better quality than no reservation –Admits more flows than naïve reservation Applications –Wireless real time applications (e.g. UCoM)