Traffic Sensitive Active Queue Management

1. Traffic Sensitive Active Queue Management - Mark Claypool, Robert Kinicki, Abhishek Kumar Dept. of Computer Science Worcester Polytechnic Institute Presenter – Ashish Samant

2. Introduction • Internet was not designed to support application based quality of service (QoS). • Best effort model • No performance guarantees • Active Queue Management (AQM) helps deal with congestion at routers, but is not enough. • No per application QoS • Not sensitive to delay/throughput needs • Our goal, “to add per application based QoS to AQM, over current best effort Internet”. 8th IEEE Global Internet Symposium

3. Introduction Spectrum of QoS Requirements of Applications Streaming Video Interactive Video Throughput Sensitivity File Transfer Streaming Audio Web-browsing Interactive Audio Gaming Electronic Mail Delay Sensitivity 8th IEEE Global Internet Symposium

4. Introduction • Problems with previous approaches to AQM: • Static classification • Per flow state maintenance • Pricing, policing overhead • Features of Traffic Sensitive QoS (TSQ): • Allows applications to indicate delay/throughput sensitivity at packet level. • Can be deployed over existing AQM schemes. • No significant addition to overhead at routers. 8th IEEE Global Internet Symposium

5. Outline • Introduction • TSQ Mechanism • Application Quality Metrics • Experiments and Results • Future Work 8th IEEE Global Internet Symposium

6. TSQ Mechanism Router Routing Table Packet queue 3 2 1 4 8th IEEE Global Internet Symposium

7. TSQ Mechanism + Rate + q AQM 10 Mbps + q (hint) = q’ q’ TSQ p + = 5 Mbps p’ Packet queue 10 Mbps 8th IEEE Global Internet Symposium

8. TSQ Mechanism • On receiving each packet, router calculates a weight : w = (d * td ) / 2N + ta d = delay limit td = drain time N = no. of bits used to represent delay hints ta = arrival time • Weight of packet determines it’s position in router queue. • Lower delay hint leads to lower weight. • Time of arrival prevents starvation. 8th IEEE Global Internet Symposium

9. TSQ Mechanism • TSQ uses “cut-in-line” scheme to insert packets with high delay sensitivity (higher weights) towards the front of the queue. • Packets from throughput sensitive application are delegated to the back of the queue • Packets that “cut-in-line” are dropped with a higher probability to ensure fairness. • Thus, advantage of labeling packets with high delay hints is neutralized with higher drop rates. 8th IEEE Global Internet Symposium

10. TSQ Mechanism • The underlying AQM has a drop probability (p) that is applied uniformly to all packets. • Delay sensitive packets receive higher drop probability : p’ = [(l + q)2 * p ] / (l + q’)2 l = one way delay q = instantaneous queue position q’ = new queue position p = drop probability calculated by underlying AQM • Packets that “cut-in-line” more will have a higher drop probability. 8th IEEE Global Internet Symposium

11. Outline • Introduction • TSQ Mechanism • Application Quality Metrics • Experiments and Results • Conclusion and Future Work 8th IEEE Global Internet Symposium

12. Application Quality Metrics • Based on previous work, we measure application quality as minimum of it’s delay quality (Qd) and throughput quality (Qt) : Q(d,t) = min(Qd, Qt) { 0 ≤ Q(d,t) } • Higher value of Qd indicates the application is more sensitive to delay and vice versa. • Application quality is normalized between 0 and 1 - 1 indicates highest quality and 0 means no quality at all. 8th IEEE Global Internet Symposium

13. Application Quality Metrics Interactive Audio Delay Quality Refs [Act02][IKK93] Excellent Quality Good Quality Excellent Quality Bad Quality Good Quality Bad Quality 8th IEEE Global Internet Symposium

14. Application Quality Metrics Interactive Audio Throughput Quality Refs[Cor98] 8th IEEE Global Internet Symposium

15. Outline • Introduction • TSQ Mechanism • Application Quality Metrics • Experiments and Results • Conclusion and Future Work 8th IEEE Global Internet Symposium

16. Experimental Setup PI, PI+TSQ AQM Queue Size 800packets qref 200 packets Network Topology S1 D1 50 Mbps, 50 ms S2 50 Mbps, 50 ms D2 R1 R2 B Mbps SN-1 DN-1 DN SN 8th IEEE Global Internet Symposium

17. Experimental Setup • PI parameters : a = 0.00001822, b = 0.00001816, w = 170 Hz, qref = 200 packets, qmax= 800 packets. • Average packet size = 1000 bytes. • All experiments run for 100 seconds • TSQ parameters : l = 40 ms. This is one-way delay constant parameter. 8th IEEE Global Internet Symposium

18. Experiment – Interactive Audio • Experiment 1: Interactive Audio • Bottleneck link bandwidth = 15 Mbps • 100 sources and 100 destinations. One way propagation delay = 150 ms • 99 TCP based file transfer flows using delay hint = 16 • 1 TCP friendly CBR source sending at 128 Kbps, with varying delay hints. 8th IEEE Global Internet Symposium

19. Analysis – Interactive Audio Analysis - Interactive Audio ( Delay ) • Low median queuing delay for lower delay hint. • Less variation in queuing delay at lower delay hints. • Delay Quality increases as delay hints decrease. 8th IEEE Global Internet Symposium

20. Analysis – Interactive Audio • Throughput measured every RTT (300 ms). • Median throughput low for lower delay hints. 8th IEEE Global Internet Symposium

21. Analysis – Interactive Audio Overall Quality • Overall quality is minimum of delay and throughput quality. • Maximum quality occurs when delay hint is 6. 8th IEEE Global Internet Symposium

22. Conclusions • TSQ provides a per-packet QoS to Internet applications. • It is a best-effort service without any guarantees. • Trade-off between throughput and delay is maintained by adjusting queue position and drop probability. • Does not require complex modifications at the router, over those needed for the AQM. 8th IEEE Global Internet Symposium

23. Future Work • Derive quality metrics for other applications like network games, instant messaging, peer to peer. • Develop applications to dynamically change their delay hints. • Investigate optimum number of bits to be used for delay hints. • Apply TSQ to other domains, for e.g. wireless. 8th IEEE Global Internet Symposium

24. Questions or Comments ? Thank you ! 8th IEEE Global Internet Symposium