1. Receiver Driven Bandwidth Sharing for TCP Authors: Puneet Mehra, Avideh Zakor and Christophe De Vlesschouwer University of California Berkeley. Presented at: INFOCOM 2003. Twenty-Second Annual Joint Conference of the IEEE Computer and Communications Societies.

2. Overview of the Presentation Motivation Goals Proposed Method NS-2 Simulations Conclusion

3. Motivation Most Internet traffic is TCP HTTP, FTP, P2P, Multimedia streaming… In many cases access links are bottleneck Limited Bandwidth (B/W) eg: DSL/Cable < 1.5Mbps User run many apps that compete for B/W Problem: TCP shares bottleneck B/W according to RTT Not fair to flows with large RTT Doesn’t consider application needs or user prefs!

4. Example: INTERNET High RTT Low RTT Med. RTT Video traffic FTP P2P Congestion

5. Goals Achieve full utilization of the receiver’s access link (bottleneck). Satisfy user preferences: -priorities assigned to each flow. Approach: limit throughput of low- priority flows to provide additional B/W for high-priority ones

6. Overview of the Presentation Motivation Goals Proposed Method NS-2 Simulations Conclusion

7. TRAS Target Rate Allocation Sub- System FCS 1 Flow Control System FCS n Flow Control System σ Calculation Sub-System σ User Preferences BWSS Bandwidth Sharing System T1T1 TnTn Internet Sender n Sender 1 RnRn RnRn R1R1 R1R1 W n & d n W 1 & d 1 For the receiver σ = system target bit-rate For the n th connection W n = Advertised Window d n = Delay in ACK packets T n = Target Rate R n = Measured Rate System Overview............

8. System Overview… Band-Width Sharing System (BWSS) consists of: a) Flow Control System (FCS) b) Target Rate Allocation Sub-system (TRAS) c) σ Calculation Sub-system.

9. FCS 1 Flow Control System T1T1 R1R1 d1d1 W1W1 For the n th connection W = Advertised Window d = Delay in ACK packets R = Measured Rate P = Packet size in bits T i = Target Rate m i = minimum bandwidth w i = weight Calculate Target Rate – Measured Rate Measure Bit-rate and RTT Adapt Receiver Window / ACK Delay Flow Control System

10. Flow Control System… R i < T i : search for the smallest W i to achieve (1- α )T i =< R i =< (1+ α )T i If R i > (1+α)*T i then delay the ACKs as decreasing W i is ineffective. Aim to minimize delay : otherwise results in unresponsiveness & instability in TCP flow.

11. Window size limits the data rate : Max Window size = min (cwnd max, receiver’s adv. window) Receiver’s advertised window After fast recovery Example Slide borrowed from Dr. Nitin Vaidya’s TCP tutorial

12. RTT and Bandwidth estimation TCP timestamp option to estimate RTT. Bandwidth estimation relies on exponentially weighted moving average R  α*R + (1-α)*R ø Ø – bandwidth estimation period, tradeoff between accuracy of estimation and time for convergence.

13. Target Rate Allocation System Some apps need minimum guaranteed rate(video), others don’t (ftp) User assigns each flow: Priority (p i ), minimum rate (m i ) and weight (w i ) Bandwidth allocation algorithm: Satisfy minimum rate in decreasing order of priority Remaining B/W shared according to weight T1T1 User Prefs. σ TnTn Prevents starvation of low priority connection

14. σ – Calculation Subsystem R1R1 RNRN U = Σ i R i σ Goal: Choose σ to maximize link utilization. U = Σ i R i (σ) Approach: Iteratively increase/decrease σ and measure the impact on utilization σ < σ ideal implies under-utilization of the link. If σ > σ ideal, does it affect the system ?

15. Overview of the Presentation Motivation Goals Proposed Method NS-2 Simulations Conclusion

16. Example of User Preferences Time 0: Min. Rate = 0 Kb/s weights = 1,2,3 for S0-S2 Priority -> S0 (max), S2(min) Time 300: Min Rate = 600 Kb/s TCP BWSS

17. Network-Congestion Example Priorities: increasing from S0-S2 Min Rate: S0,S2 – 600Kb/s S1 – 100 Kb/s Time 400s to 1200s 700Kb/s Interfering TCP traffic S2 limited to 300Kb/s

18. Multimedia Streaming Example S0 – Ftp traffic. Low Priority Min Rate = 700Kb/s S1 – Streaming at 450Kb/s High Priority 300Kb/s UDP flow (400s-1000s)

19. Overview of the Presentation Motivation Goals Proposed Method NS-2 Simulations Conclusion

20. BWSS allows user to allocate link B/W Flexible B/W allocation model Adapts to changing network conditions No changes to TCP/senders/routers Observation: - works only if desired rate is achievable under flow’s cwnd - What was receiver window advertisement actually designed for??

21. Observation: TCP window management 1 Ack1 win4 2 4 3 4 5 6 DATA3 ~ 6 win4 Data1 win4 8 Ack6 win2 9 10 11 DATA10 ~11 win4 senderreceiver

22. Questions??