JPH0370939B

PURPOSE:To attain the communication of closed zone having a high secrecy by conducting mutual communication in a short time when a channel is formed without forming the channel at all times even if the communication is attained with the communication system having a strong directivity. CONSTITUTION:A call from a telephone set 22 of a fisherboat 2 is converted once into a low bit rate by a mobile body interface circuit 20 and stored, and when a transmission line between a light transmission/receiving section 16 of the fisherboat 2 and a light transmission/receiving section 8 of a mother ship 1 is formed, the call is transferred to a mobile body interface circuit 12 of the mother ship 1 in a high speed of, e.g., 64 kbit/sec x n-bit rate. Thus, the call time being a channel forming time required to transmit the talking information in this case is a short time of nearly 2.3sec. The mobile body interface circuit 12 of the mother ship 1 stores once the transmitted talking information, converts it into sound information in 2.4 kbit/sec, reads it and restores the information into voice. Then, the PCM coding of 64 kbit/sec is applied and the result is connected to a digital exchange 4.