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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
“When considering how to reduce latency,the first step is to measure it.”
(Joanne Kinsella, Head of Portfolio, British Telecom)
4
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
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
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=−
8
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
9
∑ 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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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=?
13
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
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
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