Case study # 1.2 Title Acoustic noise troubles caused by switching noise of digital subscriber unit (DSU) Type of trouble Acoustic noise. Source of trouble DSU. System affected Customer's equipment. Location Customer premises. Keywords DSU, mutual coupling. Version date 2004-01-01 System configuration Acoustic noise trouble occurred at a customer's premises. The system configuration is shown in Figure 1.2-1. A remote terminal (RT) was used, as well as single mode fibres for the trunk lines. Metal lines were distributed using a metallic internal cable. Telephones, facsimile machines, and DSU were connected to the cable. There was no radio base station around the location. The electric field strength was not so high. After an ISDN service was introduced, the acoustic noise problem occurred. The line connected to the telephone was changed; however, the noise problem still continued. Beep MDF Internal cable Optical fibre RT DSU Miti(08)_F1.2-1 Figure 1.2-1 – System configuration Copyright © ITU 2010 – All Rights Reserved