1. Field of the Invention
The present invention relates to a multimedia communication apparatus capable of remote control in transmitting and receiving image and audio information.
2. Related Background Art
The conventional analog telephone line can only transmit voice information in the telephone communication, and data transmission can only be made at a low speed.
However, with the recent advancement in the fields of communication, semiconductor and optical communication, digital communication lines have been developed and have enabled the high-speed transmission of data of a large amount.
The digital transmission, being featured by that the quality of data can be maintained at a same level without loss in the course of transmission and that various media can be unified as a data transmission channel matching the characteristics of media is not required, and has thus realized transmission between complex media terminals. Thus, instead of the conventional telephone for transmission of voice only, there has been developed a multimedia communication apparatus capable of also transmitting the image at the same time.
The audio data to be transmitted have various formats, such as 64 Kbps (.mu.-law, A-law), 64 Kbps/56 Kbps/48 Kbps (SB-ADPCM), 32 Kbps (AD-PCM), 16 Kbps, 8 Kbps etc.
Also the transmission of image data by the digital line is made possible by data amount reduction through various band compressions such as movement compensation, frame skipping, inter- and intra-frame compensation, DCT transformation, vector quantizing transformation etc. An image encoding method, acceptable for the transfer rate of 64 Kbps which is the basic interface for the ISDN network, is the H.261 according to the ITU-T (formerly CCITT) recommendation.
For enabling mutual communication between the terminals dealing with such audio and image data, international standardization is being promoted by ITU-T (formerly CCITT) etc., and the rules for the service, protocol and multimedia multiplex frame configuration for audio visual services such as TV telephone or TV conference utilizing digital channel have been published as ITU-T (formerly CCITT) recommendations H.320, H.242, H.221 etc.
The recommendation H.221 defines the frame structure in the audio visual services from 64 to 192 Kbps, and the code allocation of FAS (frame alignment signal) and BAS (bitrate allocation signal) in the terminal ability exchange mode or in the communication mode.
Also H.242 defines the protocols for the ability exchange, communication mode switching etc. between the AV terminals employing BAS, and H.320 defines the system aspect of the AV services in general.
These recommendations define the method of multimedia communication for image, voice and data, after the setting of end-to-end physical connection and the establishment of synchronization by in-channel FAS, by means of the in-channel terminal ability exchange sequence utilizing BAS, mode switching sequence by designation of the communication mode etc.
However, adjustment of the terminal ability in each terminal according to the situation or selection of the communication mode within the exchanged ability is not contained in the definitions.
The information transfer rate of the media in the multimedia communication is determined, for the voice information, by the designation of the voice encoding method, while that for the data information is determined by presence or absence of data information and the designated transfer rate thereof in case the data information is present, and the transfer rate for image information is defined by the remainder after subtracting the transfer rates for the voice information and the data information from the entire information transfer rate of the selected communication channel.
However, the above-explained conventional multimedia communication apparatus, such as the television telephone apparatus capable of multimedia communication, in case of automatic call reception in the absence of the receiving person, can only effect a unilateral and fixed operation of transmitting a message indicating the absence of the receiver by a pre-recorded image or voice and recording and reproducing a message automatically received from the calling terminal, through the message telephone function. For operating such multimedia communication apparatus capable of automatic call reception from the calling apparatus, both the transmitting and receiving sides have to recognize and execute a particular command, so that such command will become a particular function to these specified terminals. Consequently, it has not been possible to achieve remote control from other ordinary multimedia communication apparatus.