w or aggregate, including all types of end-users. Also, performance mea- surements give inputs to the business management system and have a direct influence on different aspects of NGN operators, such as network planning and dimensioning, services marketing, and SLAs. Overall, MPM supports business processes to plan, pro- vision, operate, and maintain NGN networks and services, with the desired level of QoS provisioning. 3.6 DPI Performance Models and Metrics Deep packet inspection (DPI) performs analysis on different packet headers from layer 2 at the bottom up to the application layer on the top, as we discussed in Chapter 2. The output of a given DPI function is usually used in subsequent functions which may include reporting (on the data carried by the packet) or actions on the packet (e.g. for the purposes of QoS classification, selective charging approach for different types of services, security control to locate and stop security threats for the network or the end-users, and SO on). So, DPI is becoming an important and integral part of telecom networks. The general aspects for applying DPI technologies inside the network are typically one or several of the following [22]: 3.6 DPI Performance Models and Metrics monitoring the status of the networks network optimization and redesign improving network performance. Besides the general objectives for the DPI deployment in the network, there are cer- tain specific objectives, which include monitoring different types of traffic, identifying invalid traffic according to the policy rules, analyzing network performances, realloca- tion of network resources, or rebuilding the network based on network performance monitoring, as well as improving the satisfaction of end-users. The deployment of DPI nodes should not interrupt the performance aspects of services and applications. In theory, out-of-path DPI nodes (which analyze copies of the packets) can be implemented without interruption of services and applications. If DPI nodes are inserted on the path of packets, se