Given these performance indicators, the next step is to determine how these indicators may be measured, and how the resulting measurements can be meaningfully interpreted. At this point it is useful to look at numerous popular network management and measurement tools and examine their ability to provide useful measurements. There are two basic approaches to this task; one is to collect management information from the active elements of the network using a management protocol, and from this information make some inferences about network performance.
This can be termed a passive approach to performance measurement, in that the approach attempts to measure the performance of the network without disturbing its operation. The second approach is to use an active approach and inject test traffic into the network and measure its performance in some fashion, and relate the performance of the test traffic to the performance of the network in carrying the normal payload.
Measuring Performance with SNMP
In IP networks the ubiquitous network management tool is the Simple Network Management Protocol (SNMP).The operation of SNMP is a polling operation, where a management station directs periodic polls to various managed elements and collects the responses. These responses are used to update a view of the operating status of the network.
The most basic tool for measuring network performance is the periodic measurement of the interface byte counters. Such measurements can provide a picture of the current traffic levels on the network link, and when related to the total capacity of the link, the relative link loading level can be provided. As a performance indicator this relative link loading level can provide some indication of link performance, in that a relatively lightly loaded link would normally indicate a link that has no significant performance implications, whereas a link operating at 100 percent of total available capacity would likely be experiencing high levels of packet drop, queuing delay, and potentially a high jitter level. In between these two extremes there are performance implications of increasing the load. Of course it should be noted that the characteristics of the link have a bearing on the interpretation of the load levels, and a low-latency 10-Gbps link operating at 90-percent load will have very significantly lower levels of performance degradation than a 2-Mbps high-latency link under the same 90-percent load.
Measuring Performance with SNMP
In IP networks the ubiquitous network management tool is the Simple Network Management Protocol (SNMP).The operation of SNMP is a polling operation, where a management station directs periodic polls to various managed elements and collects the responses. These responses are used to update a view of the operating status of the network.
The most basic tool for measuring network performance is the periodic measurement of the interface byte counters. Such measurements can provide a picture of the current traffic levels on the network link, and when related to the total capacity of the link, the relative link loading level can be provided. As a performance indicator this relative link loading level can provide some indication of link performance, in that a relatively lightly loaded link would normally indicate a link that has no significant performance implications, whereas a link operating at 100 percent of total available capacity would likely be experiencing high levels of packet drop, queuing delay, and potentially a high jitter level. In between these two extremes there are performance implications of increasing the load. Of course it should be noted that the characteristics of the link have a bearing on the interpretation of the load levels, and a low-latency 10-Gbps link operating at 90-percent load will have very significantly lower levels of performance degradation than a 2-Mbps high-latency link under the same 90-percent load.
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