25-08-2017, 09:32 PM
Performance Evaluationof Computer Networks
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Performance Evaluation
Historically, performance evaluation was initially concerned with computer systems.
During the 1970’s and 1980’s, computer system performance evaluation emerged as an essential component of Computer Science due to rapid and concurrent advancements in computer hardware and computer operating systems.
The resultant increased complexity of modern computer systems made understanding and evaluating computer systems more difficult.
Performance Evaluation
Performance evaluation is the application of the scientific method to the study of computer systems.
Viewed as distinct from computer system design, the goal of performance evaluation is to determine the effectiveness and fairness of a computer system that is assumed to work correctly.
Performance evaluation techniques have been developed to accurately measure the effectiveness with which computer system resources are managed while striving to provide service that is fair to all customer classes.
Outline
Performance Evaluation
Computer Network Performance Metrics
Performance Evaluation Techniques
Workload Characterization
Simulation Models
Analytic Models
Empirical Measurement Studies
What to measure?
Choice of measurement tools
The Design of Measurement Experiments
Computer NetworkPerformance Metrics
Metric :: a descriptor used to represent some aspect of a computer network’s performance.
The goal is objective performance indices.
For computer networks, metrics can capture performance at multiple layers of the protocol stack, e.g.,
UDP throughput
IP packet round trip time
MAC layer channel utilization
Performance metrics can be positive and negative.
e.g., goodput, packet loss rate, MAC layer retries
Outline
Performance Evaluation
Computer Network Performance Metrics
Performance Evaluation Techniques
Workload Characterization
Simulation Models
Analytic Models
Empirical Measurement Studies
What to measure?
Choice of measurement tools
The Design of Measurement Experiments
Performance Evaluation Techniques
Workload characterization for computer networks involves the design and choice of traffic types that provide the inputs for computer network performance evaluation.
Performance measures of computer networks are all dependent to some extent on the input workload, the network topology and the choices in controlled parameters or network default settings.
An evaluation study of a computer network seeks to determine the values for network performance indices under a given traffic workload and network configuration.
Typical Network Traffic Types
Web Traffic between a Browser and an Internet Server.
Long-Lived File Transfers
FTP downloads.
Multimedia Streaming
Video clip downloads (UDP and/or TCP)
Audio VOIP (Voice Over IP)
Peer-to-Peer Exchanges
Concurrent downloads and uploads
Telnet file edits
Performance Evaluation Techniques
Models
Simulation Modeling
Analytic Modeling
Both modeling techniques tend to rely on queuing theory.
Measurement Studies
Empirical measurement of real networks
Measurements where some aspect of the network architecture or topology is emulated via software or hardware.
The primary focus of this presentation is on the design and techniques used in experiments to measure real computer networks.
Conceptual Models
Researchers utilize knowledge about the interactions of network components to understand and explain the workings of a computer network via a conceptual model.
Models are partitioned into simulation models or analytic models. Both model types rely on simplifying assumptions that that enable the model to capture important characteristics of networks (usually in terms of networks of queues).
Simulation Models
Simulation attempts to reproduce the behavior of the network in the time domain.
Event-driven simulation defines a network in terms of states and transitions where events trigger transitions.
Simulation is essentially a numeric solution that utilizes systems of equations and data structures to capture the behavior of the simulated network in terms of logical conditions.
Simulation Models
The three types of simulators are:
Trace-driven
Program-driven
Distribution-driven
The choice of the duration of a simulation run is subject to the same issues of estimating variance and variance reduction as found in the design of empirical measurements.