Patent ID: 6992977

Claim:
A plurality of transmission apparatuses each of which functions as a sending side transmission apparatus and a destination transmission apparatus; each of said plural transmission apparatuses being connected to terminals through an asynchronous network; said plural transmission apparatuses being interconnected through plural transmission lines each formed by a synchronous network; asynchronous data from one of said terminals being transmitted from said sending side transmission apparatus to said plural transmission lines after simultaneous conversion from said asynchronous data to synchronous data; said destination transmission apparatus selecting one of plural reception lines of said synchronous network; and said destination transmission apparatus converting said synchronous data to said asynchronous data and transmitting said asynchronous data to one of terminals through said asynchronous network; each of said transmission apparatuses comprising: a means for selecting one of reception lines each formed by said synchronous network; a means for transmitting a communication confirming frame to said synchronous network at least at a predetermined period; a communication confirming table for storing each reception time of said communication confirming frame received through said synchronous network, corresponding to each of said reception lines; and a means for deciding occurrence of failure on said reception line corresponding to said reception time when a difference between a reception time stored in said table and a present time at said predetermined period exceeds a predetermined value, and transmitting instructions of switching said reception line to said reception line selecting means.