Abstract: When a service receiving server 1 receives a request of a multi-point communication service from communication terminals 3A to 3C, a service ID corresponding to the multi-point communication service and passwords are respectively sent to the communication terminals 3A to 3C receiving the multi-point communication service and are sent to a communication service unit 2. When the communication service unit 2 receives the service ID and the password from the communication terminals 3A to 3C, the communication service unit 2 collates whether or not the service ID and the password sent from the communication terminals 3A to 3C agree with those sent from the service receiving server 1. In case of the agreement, the communication service unit 2 connects with the group of communication terminals 3A to 3C and provides the multi-point communication service for the communication terminals 3A to 3C according to the service ID.

Abstract: A service receiving unit 1 receiving a request of a multi-point communication service from a communication terminal 3A sends call-in addresses of all communication terminals 3A, 3B and 3C and a command instructing the provision of the multi-point communication service to a communication service unit 2. The communication service unit 2 sends a call to each communication terminal according to the call-in address and the command and provides the multi-point communication service. An accounting information server 4 performs the accounting to demand a communication charge and a service providing charge on the communication terminal 3A, the communication terminals 3A, 3B and 3C or a third person according to information of both a communication time-period and the number of communication terminals sent from the service receiving unit 1. Each charge is fixed or changed in proportion to or in inversely proportion to the number of communication terminals.

Abstract: In multimedia communication between a data sending device and a data receiving device through a communication line, a line state relating to transmission quality in the communication line is always detected in the data sending device, an operation mode corresponding to an error tolerance level optimum to the current line state is selected in the data sending device, pieces of media data are multiplexed to a stream of multiplexed media data according to a data multiplexing method relating to the selected operation mode, and the stream of multiplexed media data is sent to the data receiving device through the communication line. Because the line state changes with time, the data multiplexing method also changes with time. When the line state deteriorates, a data multiplexing method corresponding to a high error tolerance level is adopted. Also, when the line state ameliorates, a data multiplexing method corresponding to a low error tolerance level is adopted.