To provide a wide range of applications to a variety of users, NTT plans to introduce a global ATM backbone network and a global mega-media network (GMN) in Japan. This paper describes these new global networks and discusses technical issues for ATM and IP network performance and QoS. These issues include ATM cell and IP packet transfer performance and availability performance and related standardization by ITU-T. Also described are original techniques developed by NTT for designing network availability to improve satisfaction of telecommunication customers.

This paper focuses on how transmission error performance can be evaluated by parameters such as errored seconds (ES) and severely errored seconds (SES), under in-service conditions. Currently, attention is being paid to In-Service Monitoring (ISM) as an effective measurement technique for the error performance in digital networks. So the paper, first of all, overviews error performance parameters and shows the concept of ISM. It next discusses estimation methods for the error performance of digital channels by using information on anomaly and defect events in transmission systems. Furthermore, the paper refers to the potential usage of ISM for service quality estimation and performance assurance.>

In wideband audio teleconference systems, speech quality may be degradated due to acoustic echo in the conference room. Echo control devices such as an echo canceller can be used to improve the speech quality. This paper describes echo return loss required for acoustic echo cancellers based on subjective assessment. In particular for talker echo, subjective evaluation was pursued using a simulated wideband audio teleconference system constructed in our laboratory. Test conditions were combinations of transmission delay and insertion loss against echo path. The thresholds of detectable and/or objectionable echoes based on subjective evaluation are clarified.