A field trial of a network-integrated speaker verification system was performed in the NYNEX public switched telephone network in 1993-94. Speaker verification was performed on all calling-card calls placed by NYNEX customers who took part in this trial. Subsequently, a comprehensive impostor field-trial was performed. A variety of phones, channel conditions and caller/calling environments were represented in this large field-trial. The results show that this system performed very well under these real-world conditions. A valid user rejection rate of 1%, which is operationally very desirable, produced an equally low dedicated impostor acceptance of 3.9%. User surveys showed high user preference of this type of service. The paper discusses the results of the field trial in detail.
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