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

8th IEEE Global Internet Symposium 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 Throughput Sensitivity Delay Sensitivity Electronic Mail File Transfer Web-browsing Streaming Audio Streaming Video Gaming Interactive Video Interactive Audio

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

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

8th IEEE Global Internet Symposium 8 TSQ Mechanism  On receiving each packet, router calculates a weight : w = (d * t d ) / 2 N + t a d = delay limit t d = drain time N = no. of bits used to represent delay hints t a = 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 ( Q d ) and throughput quality ( Q t ) : Q(d,t) = min(Q d, Q t ) { 0 ≤ Q(d,t) }  Higher value of Q d indicates the application is more sensitive to delay and vice versa.  Application quality is normalized between 0 and indicates highest quality and 0 means no quality at all.

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

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 Network Topology S1 S2 SN-1 SN Queue Size PI, PI+TSQ AQM 800 packets q ref 200 packets R1 50 Mbps, 50 ms D1 D2 DN-1 DN R2 50 Mbps, 50 ms B Mbps

8th IEEE Global Internet Symposium 17 Experimental Setup  PI parameters : a = , b = , w = 170 Hz, q ref = 200 packets, q max = 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 !