Patent ID: 7519072

Claim:
A transmission system comprising: a plurality of concentrated subscriber line transmission apparatuses, each accommodating a plurality of user terminals; and a relaying apparatus located between said concentrated subscriber line transmission apparatuses and a communication network, wherein said relaying apparatus comprises: a first buffer memory for buffering control requests to be transmitted to said concentrated subscriber line transmission apparatuses, a second buffer memory for buffering download data to be transmitted to one of said concentrated subscriber line transmission apparatuses, a control unit for generating a maintenance frame including a control request read out from said first buffer memory, and download frames each including download data read out from said second buffer memory, and transmitting these frames to a specific one of said concentrated subscriber line transmission apparatuses selectively, wherein said control unit controls the transmission of said download frames, depending on the status of traffic of communication frames being relayed from said communication network toward said specific one of concentrated subscriber line transmission apparatuses and on the buffering status of control requests awaiting transmission in said first buffer memory, and an interface board for relaying communication frames between said concentrated subscriber line transmission apparatuses and the communication network, and a control board connected to said interface board, wherein said first and second buffer memories and said control unit are mounted on said control board, wherein said interface board comprises: an upward signal processing circuit for relaying upward communication frames from said concentrated subscriber line transmission apparatuses to said communication network, a downward signal processing circuit for relaying downward communication frames from said communication network to said concentrated subscriber line transmission apparatuses, and a status monitor for detecting status of traffic of downward communication frames, and wherein said control unit determines timing to transmit each of said download frames, depending on the status of traffic detected by said status monitor and on the buffering status of control requests awaiting transmission in said first buffer memory and delivers the download frame to said downward signal processing circuit.