IMPROVEMENTS RELATING TO VIDEO TELEPHONY

摘要

In a videophone a method of transmitting simultaneously video and audio data over a PTSN uses a first modem (31) which is connected to the PTSN to transmit by analogue means data by a data compression technique to a second modem. Each modem (31) has associated with it a controller (32) linked to a respective audio unit (33) and a video unit (34). Each audio unit (33) is arranged to transmit fixed sized data packages in a synchronous mode and each video unit (34) is arranged to transmit a variable bit stream of variable length in an asynchronous mode. Each controller (32) is capable of transmitting data in packs in a data frame comprising 5 packs, the audio data is contained in 4 fixed sized data packs of 160 bits of data and the video data packet is contained within a single data pack.