Now-a-days cellular technology is emerging rapidly. Based on the demand of the users, next generation cellular system is being able to provide a variety of applications for users’ satisfaction. The Universal Mobile Telecommunication (UMTS) System is one of the features of cellular communication which is able to yield the different types of services as per users’ satisfaction. Real-time applications such as Video and voice conferencing have a great deal of demand over the cellular network. The quality of service (QoS) is the major concern for real time application such as voice and video telephony. In order to fulfill the users’ demand, it is necessary to improve the QoS. In this thesis work, we analyze and evaluate the performance of existing QoS for voice and video transmission over 3G/UMTS networks. The performance is evaluated based on some QoS parameters such as packet loss, delay, throughput and jitter. In order to investigate the performance of existing QoS scheme in UMTS network, we analyze the simulation results. The investigation illustrates that proper adaptation of QoS provides qualitative transmission in voice and video telephony. Finally on the basis of the simulation results, we study the QoS performance and propose integration scheme to enhance the QoS performance in 3G/UMTS network based on existing QoS parameters. This frame work will be effective to design the QoS for heterogeneous network in B3G/4G.