Noise Can Help: Accurate and Efficient Per-flow Latency Measurement without
Packet Probing and Time Stamping
Dept. of Computer Science and EngineeringMichigan State University
East Lansing, Michigan, 48824, USA
Muhammad Shahzad Alex X. Liu
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Latency Matters! Applications
─ Financial trading─ HPC
Architecture─ CDNs─ Data centers
“When considering how to reduce latency,the first step is to measure it.”
(Joanne Kinsella, Head of Portfolio, British Telecom)
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Flow 1 = 1msFlow 2 = 1msFlow 3 = 1.25msFlow 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
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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
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Problem Statement Input
─ Relative error ─ Success probability
Output─ An estimate of average latency such that
─ An estimate of standard deviation in latency such that
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Basic Idea Total latency of a flow with packets is
Recording Phase Querying Phase
∑∀𝑘
𝑡𝑅𝑘 ,∑∀𝑘
𝑡𝑅𝑘 ,∑∀𝑘
𝑡𝑅𝑘 ,∑∀𝑘
𝑡𝑅𝑘∑
∀𝑘
𝑡𝑆𝑘 ,∑∀𝑘
𝑡𝑆𝑘 ,∑∀𝑘
𝑡𝑆𝑘 ,∑∀𝑘
𝑡𝑆𝑘∑
∀𝑘
𝑡𝑆𝑘 ∑
∀𝑘
𝑡𝑅𝑘
𝐿𝑎𝑡𝑒𝑛𝑐𝑦=−
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Recording Phase: a naïve solution
0 0 0 0 0 0 0 0 0 0 0 0067
670 5
5
8
13
10
1052 76 38 69 8553
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 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
0 0 0 0 0 0 0 1 1 1
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∑ 𝑎𝑙𝑙𝑐𝑜𝑢𝑛𝑡𝑒𝑟𝑠≥𝑇⇒𝐷𝑢𝑚𝑝𝑡𝑜𝑝𝑒𝑟𝑚𝑎𝑛𝑒𝑛𝑡 𝑠𝑡𝑜𝑟𝑎𝑔𝑒
Recording Phase: COLATE Map multiple flows to each counter Map each flow to multiple counters Many-Many mapping
─ Map each flow to out of counters
When a packet comes─ Select random number ─ Evaluate hash ─ Add time stamp counter number ─ Dump when sum of counters exceeds a threshold
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 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
0 0 0 0 0 0 0 1 1 1
Cost per packet:─ One hash computation─ One memory update
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Querying PhaseLatency of Flow ?
Extract Extract
𝐸 [ ]=∑∀ 𝑘
𝑡𝑆𝑘
𝑚𝐸 ¿
Latency =
Take average
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𝑏=?
𝑚=?
𝑛=?
Optimal Parameter Selection Four unknown parameters
─ Number of counters ─ Number of counters each flow maps to─ Size of each counter ─ Threshold
𝑇=∑ 𝑎𝑙𝑙𝑐𝑜𝑢𝑛𝑡𝑒𝑟𝑠=?
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Optimal Parameter Selection Four equations
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Performance Evaluation Network Traces
Simulated queue traversal to get departure timestamps─ RED queue management strategy
Trace Duration No. of Packets
No. of Flows
CHIC 5 mins 37.3M 3.01M
ICSI 41.1 hrs 46.9M 0.387M
DC 1.08 hrs 19.9M 0.439M
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Accuracy
α=0.99 , β = 0.01 α=0.9 5 , β = 0.05
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Comparison with RLI Implemented RLI (SIGCOMM’10)
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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
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Questions?
