On the Quality of Computer Network Measurements

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(1)Due to the complex diversity of contemporary Internet-services, computer network measurements have gained considerable interest during the recent years. Since they supply network research, development and operations with data important for network traffic modelling, performance and trend analysis, etc. The quality of these measurements affect the results of these activities and thus the perception of the network and its services. This thesis contains a systematic investigation of computer network measurements and a comprehensive overview of factors influencing the quality of performance parameters obtained from computer network measurements. This is done using a novel network performance framework consisting of four modules: Generation, Measurement, Analysis and Visualization. These modules cover all major aspects controlling the quality of computer network measurements and thus the validity of all kinds of conclusions based on them. One major source of error is the timestamp accuracy obtained from measurement hardware and software. Therefore, a method is presented that estimates the timestamp accuracy obtained from measurement hardware and software.The method has been used. to evaluate the timestamp accuracy of some commonly used hardware (Agilent J6800/J6830A and Endace DAG 3.5E) and software (Packet Capture Library). Furthermore, the influence of analysis on the quality of performance parameters is discussed. An example demonstrates how the quality of a performance metric (bitrate) is affected by different measurement tools and analysis methods. The thesis also contains performance evaluations of traffic generators, how accurately applicationlevel measurements describe network behaviour, and of the quality of performance parameters obtained from PING and J-OWAMP. The major conclusion is that measurements systems and tools must be calibrated, verified and validated for the task of interest before using them for computer network measurements. A guideline is presented on how to obtain performance parameters at a desired quality level.. ON THE QUALITY OF COMPUTER NETWORK MEASUREMENTS. ABSTRACT. Patrik Arlos. Keywords: Computer Network Measurements, Network Measurement Accuracy, Timestamp Accuracy, Quality of Measurements, Traffic Generation, Analysis, Sampling.. Patrik Arlos. ISSN 1653-2090 ISBN 91-7295-070-6. 2005:05. 2005:05. ON THE QUALITY OF COMPUTER NETWORK MEASUREMENTS. Blekinge Institute of Technology Doctoral Dissertation Series No. 2005:05 School of Engineering.

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(230) MDI Meduim. 10 Mbps. Meduim 1 Mbps 10 Mbps. PMA. 1000 Mbps. Meduim. MDI. PMD. PMA. PCS. GMII. RECONCILIATION. > ::: 8! 5+ + '. PLS = Physical Layer Signaling PCS = Physical Coding Sublayer PMA = Physical Medium Attachment PHY = Physical Layer Device PMD = Physical Medium Dependent. 100 Mbps. Meduim. MDI. PMD. PMA. AUI. MII PCS. MII PLS. RECONCILIATION. RECONCILIATION. MDI. PMA. AUI. PLS. MAC — Media Access Control. MAC Control (Optional). LLC — Logical Link Control. AUI = Attachment Unit Interface MDI = Medium Dependent Interface MII = Media Independent Interface GMII = Gigabit Media Independent Interface MAU = Medium Attachment Unit. Physical. Data Link. Network. Transport. Session. Presentation. Application. OSI Reference Model Layers. LAN CSMA/CD Layers Higher Layers.

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