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?