With the rapid development of network technology, deployment of real-time applications such as video, voice and Virtual Reality over network become more popular than ever. However, the best effort model, existing over Internet cannot satisfy the QoS requirements of real-time applications. In order to make Internet Quality of Service (QoS) capable, IETF proposed a series of protocols and algorithms, some of them forming what is known as "Differentiated Services". In this paper, we focus on analyzing the performance of real-time applications over a Diffservcapable network, especially when real-time traffic aggregation and link congestion case happen in core router. Based on extensive testing results we propose a novel scheduling scheme, which can solve the problem generated by EF traffic aggregation and link congestion. Based on our findings, we conclude that with proper resource management and traffic engineering, differentiated services can provide satisfactory QoS to real-time applications with strict delay, delay variation, packet loss and throughput constraints.