Abstract: Video data is coded at either a minimum transfer rate or maximum transfer rate and stored in a storage unit as a video reply message. In a case where the video data has been coded at the minimum transfer rate and stored, the video reply message is transmitted upon being multiplexed with an audio reply message if the actual transfer rate agrees with the minimum transfer rate. If the two transfer rates are different, invalid bits conforming to the difference between the rates are generated and the invalid bits, the audio reply message and the video reply message are multiplexed and transmitted. In a case where the video data has been coded at the maximum transfer rate and stored, on the other hand, the video reply message is decoded when an incoming call arrives, the video data thus obtained is coded based upon the actual transfer rate, and the video reply message obtained by coding is multiplexed with the audio reply message and transmitted.

Abstract: A receiver unit for a data transmission system, where transmitted data signals are accompanied by overhead signals, comprises processor means with one or more processors for processing said overhead signals as well as RAM type storage means, in which the processor means can store the data which are obtained by the processing of the overhead signals. Further, between the arriving overhead signals and the processor means there is a buffer circuit, in which the overhead signals can be temporarily placed prior to their processing, and from which the processor means can fetch the signals as the processor means become ready to process the signals.