A major challenge in future mobile networks is how to fulfil the requirements set for 5G networks in terms of latency and throughput. 3GPP has defined a new architecture based on virtualization and Software Defined Networks (SDN) supporting network slices that can fulfil those requirements. In this paper, we present the first realization of the new 5G user plane function (UPF) component that supports SDN and provides optimized transport for reducing latency as required in 5G networks. The proposed UPF is the cornerstone for using different data transport strategies adapted to the needs of different verticals, such as Ultra Reliable Low Latency Communications (URLLC) services that require a separate network slice providing an optimized transport for URLLC applications. The paper also discusses how to best migrate from legacy 4G user plane to 5G UPF, so as to ensure a reasonable transition to 5G. In doing so, the objective is not to meet short-term needs but to fulfill the future latency and throughput requirements of emerging applications, and also to provide first performance results of UPF in a realistic testbed environment.1