Video telephone service (VTS) is considered one of promising services provided in wideband CDMA (WCDMA) networks. Without a designated call admission policy, VTS calls are expected to suffer from relatively high probability of blocking since they normally have more stringent signal quality requirement than ordinary voice calls. In this letter, we consider a prioritized call admission design in order to reduce the blocking probability of VTS calls, which may encourage the users to access the newly-provided VTS in a more comfortable way. The VTS calls are given a priority by reserving a number of channel-processing equipments. With the reservation, the blocking probability of prioritized VTS calls can be reduced evidently. That of ordinary calls, however, is increasing instead. This letter provides a system model that counts the blocking probabilities of VTS and ordinary calls simultaneously, and numerically examines an adequate level of the prioritization for VTS calls. The results show that the prioritization level should be selected depending on received interference as well as bandwidth required for VTS.

The states-of-the-art in visual communication in Japan are described. First the status of networks, which is a basis for offering visual communication service, is outlined. Visual communication service being developed on the basis of ISDN is described. The future service can be represented by NTT's service vision VI&P. Visual communication technologies and services being studied are surveyed.