This part of the Interim European Telecommunication Standard (I-ETS) specifies the electroacoustic characteristics for 3,1 kHz bandwidth handset telephony functions implemented in videotelephony terminals. Those terminals are intended for use in the videotelephony teleservice and connected to the basic access of the coincident S and T reference point of the Integrated Services Digital Network (ISDN) using either Pulse Code Modulation (PCM) encoding according to CCITT Recommendation G.711 [1], A-law and µ-law or Low Delay code-Excited Linear Prediction (LD-CELP) coding at 16 kbit/s as specified in CCITT Recommendation G.728 [21].