According to the discovery of available and suitable audiovisual services over IP, researches on the Quality of Service (QoS) for various multimedia application services are required. This paper presents evaluation of speech quality applying improved Packet Loss Concealment (PLC) algorithms with an end-to-end bidirectional transmission control scheme. We propose real-time transmission control scheme to perform better quality monitoring of VoIP service. In order to evaluate the newly proposed RTCP-XR scheme for VoIP services, we measure in real-time the quality degree of the received speech signal while applying our improved Packet Loss Concealment (PLC) algorithms in G.711 and G.729A codecs using an implemented Session Initiation Protocol (SIP)- based SoftPhone and a 1-port gateway systems. Overall, for the evaluation with scientific exactitude of speech quality applied our PLC algorithms we examine with made phone-calls through the heterogeneous network systems. The experimental results confirm the applied PLC algorithms for improvement of speech quality over IP in real environments with the QoSfactor transmission control mechanism.