Office recognition method in ring network

A ring network has first and second network connecting offices for connecting ring networks together and for dropping a signal from a terminal office. Each node of the ring network recognizes whether it is the first network connecting office based upon channel setting information. A first node, which has been recognized as being the first network connecting office, executes a squelch-table creation procedure between itself and other nodes based upon the channel setting information, thereby identifying a second node, which is the second network connecting office. The first node embeds office identification information in a squelch table of a protection channel and sends this information to the second node. The second node recognizes that it itself is the second network connecting office based upon the office identification information.