voice and video require packets to arrive in the correct sequence order to be processed. If packets arrive out-of-order or out-of-sequence, they may have to be dropped because they cannot be inserted into the stream that has already been played. 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 the 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. These factors, and others (such as the performance of the network signaling on the end nodes, compression, encryption, concurrency, and so on) all affect the effective performance of a network. In some cases, the network may not work at all; in others, it may be slow or unusable. And because applications run over these networks, application performance suffers. Various intelligent solutions are available to ensure that traffic over the network is effectively managed to optimize performance for all users. See Traffic Shaping The performance management discipline Network performance management (NPM) 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. For example: Streaming video or voice can be unreliable (brief moments of static) but needs to have very low latency so that lags don't occur Bulk file transfer or e-mail must be reliable and have high capacity, but doesn't need to be instantaneous Instant messaging doesn't consume much bandwidth, but should be fast and reliable 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