NGN (Next Generation Network) refers to a network developed to be suitable for an environment in which there is a convergence between wired, wireless communications and broadcasting. Most telecommunication providers have a plan or are conducting a migration of their network to NGN. One of the most important issues for constructing NGN is to provide end-to-end QoS (Quality of Service). This paper aims to propose carriers, who begin to evolve their network to NGN, a construction strategy in the interests of QoS by introducing an example of nationwide NGN in Korea. In viewing the strategy, we develop converged services, and define services provided through NGN first. Next, we define our own standard of service performance metrics, network performance metrics, and quality of service policy from the transport stratum view point. Then we design and construct NGN. Finally, we verify end-to-end performance objectives comparing predefined metrics with collected measurement data on the NGN and derive improvements. This paper deals with voice and video telephony data to analyze the traffic characteristics statistically. It should be noted that voice and video are real time data and reflect the absolute need for QoS in the network.