Application of on-line test idea for avoidance of timing loop

With the extensive deployment of SDH, the architecture of synchronization transport network is more complicated. So the timing loop can not be avoided effectively only using a network plan. The existing synchronization statue message (SSM) has a certain effect on avoiding timing loop and should be improved to avoid it as possible. In this paper, the scheme "DUS for test (DUST)" is advanced as an option to the enhancement of SSM, and simulated on a network model, the further refinements are also discussed.