Patent ID: 7471697

Claim:
A multiplex transmission system that converts data from a client device that have been encoded using particular encoding rules to data that are based on standards of a transmission path, using a converter, and then transmits said data, said system comprising: a transmission path having a predetermined transmission signal format including a plurality of data codes for transmitting data and a plurality of control codes for transmitting control information, wherein one or more values of said control codes comprises an unused control code in that there is no relation defined between said value and control information; a first client device at a first end of said transmission path, said first client devices using a predetermined interface format; a first converter coupled with said first client device, said first converter converting signals received from said first client device in said predetermined interface format into said predetermined transmission signal format and converting signals received from said transmission path in said predetermined transmission signal format into said predetermined interface format for said first client device, wherein said first client device and said first converter can serve as either a transmitting side or a receiving side; a second client device at a second end of said transmission path, said second client device using said predetermined interface format; and a second converter coupled with said second client device to convert signals to and from said predetermined transmission format and said predetermined interface format, wherein said second client device and said second converter can also serve as either a transmitting side or a receiving side, wherein, a conveter on a transmitting side comprises an encoder that uses one or more of said unused control code values to transmit to a converter on a receiving side alert information indicating that a problem has occurred between the converter on the transmitting side and the client device on the transmitting side, wherein said converter on the receiving side, upon receiving said alert information from the converter on the transmitting side, transmits a signal to the client device on the receiving side, indicating that a problem on the transmitting side has occurred.