1. Noise Can Help: Accurate and Efficient Per-flow Latency Measurement without Packet Probing and Time Stamping Dept. of Computer Science and Engineering Michigan State University East Lansing, Michigan, 48824, USA Muhammad Shahzad Alex X. Liu

2. 2 Latency Matters!  Applications ─ Financial trading ─ HPC  Architecture ─ CDNs ─ Data centers

3. “When considering how to reduce latency, the first step is to measure it.” (Joanne Kinsella, Head of Portfolio, British Telecom)

4. 4 Flow 1 = 1ms Flow 2 = 1ms Flow 3 = 1.25ms Flow 4 = 4ms  Aggregate Latency Measurement ─ Measure average latency ─ Guaranteeing average ≠ Guaranteeing each  Per-flow Latency Measurement ─ Measure latency of each flow  Applications ─ ISP operators ─ ISP customers Types of Latency Measurements Aggregate Latency = 1.7ms

5. 5 Prior Art and Limitations  Aggregate Latency Measurement ─ LDA [SIGCOMM’09] ─ FineComb [SIGMETRICS’11]  Per-flow Latency Measurement ─ RLI [SIGCOMM’10]: active probes ─ MAPLE [IMC’12]: timestamps  Commercial Solution ─ Corvil’s latency monitoring devices ─ USD 180,000 for a 2 × 10Gbps box

6. 6 Problem Statement

7. 7 Basic Idea

8. 8 Recording Phase: a naïve solution 000000000000 0 67 67 0 5 5 8 13 10 5252 7638 6985 53  One counter per flow: 1-1 mapping  Problem ─ Overflow vs. Underutilization  Reason ─ 1-1 mapping: flows counters 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 1 0 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 1 1 1

9. 9 Recording Phase: COLATE 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 1 0 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 1 1 1  Cost per packet: ─ One hash computation ─ One memory update

10. 10 Querying Phase Latency of Flow ? Take average

11. 11 Optimal Parameter Selection

12. 12 Optimal Parameter Selection

13. 13 Performance Evaluation  Network Traces  Simulated queue traversal to get departure timestamps ─ RED queue management strategy TraceDurationNo. of Packets No. of Flows CHIC5 mins37.3M3.01M ICSI41.1 hrs46.9M0.387M DC1.08 hrs19.9M0.439M

14. 14 Accuracy

15. 15 Comparison with RLI  Implemented RLI (SIGCOMM’10)

16. 16 Advantages over Prior-Art  Proposed an accurate and efficient per-flow latency measurement scheme ─ Reliable ─ Passive ─ Scalable ─ Efficient: Memory and Computations ─ Flexible  More in the paper ─ Standard deviation in latencies of packets in a flow ─ Theoretical development

17. 17 Questions?