Performance Management • enables the manager to prepare the network for the future, as well as to determine the efficiency of the current network. • involves measuring the performance of a network and its resources in terms of utilization, throughput, error rates, and response times
Factors Affecting Network Performance • Latency: It can take a long time for a packet to be delivered across intervening networks. In reliable protocols where a receiver acknowledges delivery of each chunk of data, it is possible to measure this as round-trip time. • Packet loss: In some cases, intermediate devices in a network will lose packets. This may be due to errors, to overloading of the intermediate network, or to intentional discarding of traffic in order to enforce a particular service level. • Retransmission: When packets are lost in a reliable network, they are retransmitted. This incurs two delays: First, the delay from re-sending the data; and second, the delay resulting from waiting until the data is received in the correct order before forwarding it up the protocol stack. • Throughput: The amount of traffic a network can carry is measured as throughput, usually in terms such as kilobits per second. Throughput is analogous to the number of lanes on a highway, whereas latency is analogous to its speed limit
With performance management information, a network manager can reduce or prevent network overcrowding and inaccessibility. This helps provide a more consistent level of service to users on the network, without overtaxing the capacity of devices and links. This form of management looks at the percentage of utilization of devices and error rates to help in improving and balancing the throughput of traffic in all parts of a network.
Typically, some devices are more highly utilized than others. Performance monitoring give qualitative and time relevant information on the health and performance of devices so that underutilized devices are more fully utilized, and overtaxed devices are rebalanced. In a well-utilized network with healthy components, the error rates for packets traversing the network are down and response times are shortened.
Performance Management Discipline • Network performance management consists of measuring, modeling, planning, and optimizing networks to ensure that they carry traffic with the speed, reliability, and capacity that is appropriate for the nature of the application and the cost constraints of the organization. Different applications warrant different blends of capacity, latency, and reliability.
Network performance management tasks and classes of tools • Network Performance management is a core component of the FCAPS ISO telecommunications framework (the 'P' stands for Performance in this acronym). It enables the network engineers to proactively prepare for degradations in their IT infrastructure and ultimately help the end-user experience. • Network managers perform many tasks; these include performance measurement, forensic analysis, capacity planning, and load-testing or load generation. They also work closely with application developers and IT departments who rely on them to deliver underlying network services.
For performance measurement, operators typically measure the performance of their networks at different levels. They either use per-port metrics (how much traffic on port 80 flowed between a client and a server and how long did it take) or they rely on end-user metrics (how fast did the login page load for Bob.) • Per-port metrics are collected using flow-based monitoring and protocols such as Netflow (now standardized as IPFIX) or RMON. • End-user metrics are collected through web logs, synthetic monitoring, or real user monitoring. An example is ART (application response time) which provides end to end statistics that measure Quality of Experience.