1. Electrical apparatus for line telephony or line telegraphy;
videophones有线电话、电报设备，包括有线载波通信设备；
2. Hands-free speech communication is indispensable in audio and video conference systems, hot-line telephones and videophones, digital ISDN network, mobile radio terminals etc, people demand higher and higher speech quality in communication.
免提式话音通信在移动电话、热线电话、ISDN网及车载电话的电视电话会议等多种领域正得到日益广泛的应用，人们对声音通讯系统中的话音质量提出了越来越高的要求。