Vt path misconnection avoidance method in the event of sonet failures

Abstract

Idle frames are transmitted from first and second nodes of ring network in response to a first link failure, and protection switching is performed to form a first loop between the first and second nodes via at least a third node on receiving idle frames and Bridged & Switched frames are transmitted to the first loop. At the third node, AU (administrative unit) squelching is performed in response to a second link failure in the first loop, and protection switching is performed at the third node to form a second loop between the second and third nodes, and VT squelch is performed at the third node and busy indication frames are sent from the third node to the second node until the VT (virtual tributary) squelch is completed. From the third node to the second node, Bridged & Switched frames are transmitted and the AU squelch is cleared upon completion of the VT squelch. At the second node, AU squelching is performed in response to the busy indication frames from the third node, and AT squelch is cleared in response to the Bridged & Switched frames from the third node. Alternatively, the third node performs AU squelching in response to the second link failure and performs protection switching to form a second loop between the first and third nodes, and transmits Bridged & Switched frames to the first node. In response, the first node performs AU squelching, performs VT squelching and transmits busy indication frames to the third node until VT squelching is completed, and dears the AU squelch upon completion of the VT squelching. The third node responds to the Bridged & Switched frames from the first node for clearing the AU squelch.