This paper describes experiments for evaluating the speech quality of packetized voice communications. The experimental conversations are performed through experimental packetized voice communications equipment, which provides packet transmission delays and packet losses. Three experimental results are apparent: packet losses degrade speech quality much more than packet transmission delays in PCM, packet delays affect speech quality more than packet losses in ADM, and inserting the last received codes for lost packets reduces the degradation of speech quality in PCM.

AAL2 technology, which will be used in 3rd generation mobile communications systems, can be used to efficiently transmit low-bit-rate traffic. Because user connections are multiplexed at virtual-channel connections in AAL2 networks, conventional ATM QoS management, which operates in units of VC connections, may be inadequate for managing the QoS of AAL2 connections. In this paper, we argue that for efficient utilization of network resources, it is advantageous to accommodate AAL2 connections with different QoS conditions in the same VC connection. We present a multiplexing configuration that enables QoS to be controlled at the AAL2-connection level. It works by matching the AAL2-packet-multiplexing timing to the cell-transmission timing. We also address the issue of AAL2-bandwidth management. To calculate the bandwidth, we evaluate the characteristics of multiplexing CPS packets into the ATM cell payload.