Timo-Pekka HeikkinenTKK Networking laboratory

Supervisor: Prof. Raimo KantolaInstructor: Lic. Tech. Marko Luoma

“Measuring the performance of an active network measurement

platform”

Master’s Thesis Presentation – Timo Heikkinen 28.5.2007

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Contents

› Theory part» Terms and concepts

› Practical part» Brix system

› Results› Conclusions› Future work

Master’s Thesis Presentation – Timo Heikkinen 38.5.2007

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Theory part

› Active measurements in data communication networks

› Active vs. passive measurements› Types of active measurement mechanisms

and methods› Difficulties in making active

measurements» Accuracy of measurements

Master’s Thesis Presentation – Timo Heikkinen 48.5.2007

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Terms and concepts 1

› Probe» An artificial packet containing information relevant to

the measurement (e.g. timestamp, seq. # etc.)› One-way latency (delay)

» Time it takes for a probe to travel from point A to point B in a network

› Round-trip delay» Time it takes for a probe to travel from A to B and back

to A› Delay jitter

» The amount of variation in the measured delay› Packet loss

» A packet is declared lost when it has failed to arrive to its destination in a certain amount of time

Master’s Thesis Presentation – Timo Heikkinen 58.5.2007

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› Types of delay» Processing delay

· Time it takes for a router to process a packet

» Transmission delay· Time it takes for a router to push a packet to the link

» Propagation delay· Time it takes for a signal to travel across the physical

medium

» Queuing delay· Time the packet spends inside routers’ queues

Terms and concepts 2

Master’s Thesis Presentation – Timo Heikkinen 68.5.2007

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Practical part

› Measuring the performance of an active measurement system (Brix Networks)

› Two test cases / network environments» Simple network topology

· Comparison of the Brix system versus an well-known accurate measurement system (AX4000)

» (Relatively) Complex network topology· Is Brix able to detect certain events in the network?

› Overall, how does the Brix system perform?

Master’s Thesis Presentation – Timo Heikkinen 78.5.2007

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Devices

Brix 100 Verifier

Brix 1000 Verifier

» Synchronization› Brix 1000 GPS-receiver

· Acted as an NTP-server

› Brix 100’s NTP synched› NTP synch in the complex case

· No need for GPS because RTT was measured

Master’s Thesis Presentation – Timo Heikkinen 88.5.2007

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Brix Architecture

Operations Center GUI,Subscriber portal GUI

Verifier

Verifier

Verifier

ConsolidatorCollectorLocal RegistryNetwork Registry

Test

BrixWorx

Master’s Thesis Presentation – Timo Heikkinen 98.5.2007

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Brix Reporting

Data from the Brix system

Master’s Thesis Presentation – Timo Heikkinen 108.5.2007

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Results (1/4), case 1

Cumulative probability distributions of all tested devices when measuring one-way delay. Delay shown with and without NTP-offset correction

Master’s Thesis Presentation – Timo Heikkinen 118.5.2007

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Results (2/4), case 1

Measured one-way delay between Brix 1000 and Brix 100 verifiers

Master’s Thesis Presentation – Timo Heikkinen 128.5.2007

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Results (3/4), case 2

Effects of high load on the delay measured by the Brix system

Master’s Thesis Presentation – Timo Heikkinen 138.5.2007

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Results (4/4), case 2

Core router failure as reported by the Brix system.

Master’s Thesis Presentation – Timo Heikkinen 148.5.2007

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Conclusions (1/2), case 1

› More time should have been spent on designing the test setup

› Brix 100’s are not accurate enough to measure sub-millisecond one-way delays» Clock instability big issue » Accuracy ~940 μs, ~120 μs with NTP corr.

› Brix 1000’s are accurate when using GPS synchronization» Clocks stabile enough» Accuracy ~50 μs, ~10 μs with NTP corr.

› AX4000 accuracy ~1 microsecond (when using only one clock)

Master’s Thesis Presentation – Timo Heikkinen 158.5.2007

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Conclusions (2/2), case 2

› Test parameters should have been selected more carefully

› Measurement reports are lost too often› Congestion and node failures can be

detected with Brix› Short link failures were undetected

Master’s Thesis Presentation – Timo Heikkinen 168.5.2007

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Future work

› Case 1 should be done in a more complex network environment

› Case 2 should be done with the same equipment as used in case 1

› GPS synchronized Brix 1000’s› NTP offset measurement