Due to their centralised design, current mobile network architectures as well as IMS layer will not be able to handle the increasing number of mobile users consuming high bitrate services. An Ultra Flat Architecture (UFA), based on SIP and designed with the primary goal of being scalable, has been introduced in a previous paper. In this paper, the limitations of current 3GPP architectures are discussed and detailed explanations of UFA interest and procedures are provided. UFA is entirely controlled by the operator and integrates QoS in its establishment and mobility procedures. To prove its concept and assess the performance of its mobility procedure, UFA is implemented on a testbed. UFA HO delay measured at the application level is 100ms in average; it is 12 times smaller than in a classic SIP-based mobility scheme