However,the concern is that voice traffic in frame environments built with permanent virtual circuits (PVC) will not be as cost-effective as frame nets built with switched virtual circuits (SVC).

• 但问题是，用永久虚拟电路（PVC）建立起来的帧环境中的话音通信的性能价格比不如用交换虚拟电路（SVC）建立起来的帧网络。