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Understanding Network: Performance Measurements

Evaluating path performance means doing three types of measurements. measurements will give you an idea of the hardware capabilities of your network, such as the maximum capacity of your network. BandwidthThroughput measurements will help you discover what capacity your network provides in practice, i.e., how much of the maximum is actually available. Traffic measurements will give you an idea of how the capacity is being used.

Performance Measurements

Two factors determine how long it takes to send a packet or frame across a single link. The amount of time it takes to put the signal onto the cable is known as the transmission time or transmission delay. This will depend on the transmission rate (or interface speed) and the size of the frame. The amount of time it takes for the signal to travel across the cable is known as the propagations time or propagations delay. Propagation time is determined by the type of media used and the distance involved.

Once we move to multi-hop paths, a third consideration enters the picture – the delay introduced from processing packets at intermediate devices such as routers and switches. This is usually called the queuing delay since, for the most part, it arises from the time packets spend in queues within the device. The total delay in delivering a packet is the sum of these three delays. Transmission and propagation delays are usually quite predictable and stable. Queuing delays, however, can introduce considerably variability.

The term bandwidth is typically used to describe the capacity of a link.

Throughput is a measure of the amount of data that can be sent over a link in a given amount of time. Throughput estimates, typically obtained through measurements based on the bulk transfer of data, are usually expressed in bits per second or packets or second. Throughput is frequently used as an estimate of the bandwidth of a network, but bandwidth and throughput are really two different things. Throughput measurement may be affected by considerable overhead that is not included in bandwidth measurements. Consequently, throughput is a more realistic estimator of the actual performance you will see.

Throughput is generally an end-to-end measurement. When dealing with multi-hop paths, however, the bandwidths may vary from link to link. The bottleneck bandwidth is the bandwidth if the slowest link on a path, i.e., the link with the lowest bandwidth.

The above was extracted from the book, "Network Troubleshooting Tools" by Joseph D. Sloan.

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1 Responses to “Understanding Network: Performance Measurements”

  1. # Anonymous Anonymous


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