An improved guided restoration algorithm for ATM crossconnect networks

This paper proposes the guided restoration algorithm starting at different timing (GRA-DT) which is a scaleable self-healing algorithm that takes into account the buffer size required for the self-healing OAM cells arriving at an ATM crossconnect. In the guided restoration algorithm (GRA) all self-healing processes are started just after VP-AIS cells are detected. Thus if many VPs are affected by failures, a lot of self-healing OAM cells are transmitted during a short period of time. To avoid losing such cells, ATM crossconnects must be equipped with a large size buffer to store the self-healing OAM cells waiting for processing. To reduce the buffer size, we propose the GRA-DT with which self-healing processes are started at different timing for different VPs. This scheme has the effect of dispersing self-healing OAM cell transmission in time. Thus the number of self-healing OAM cells waiting in a buffer decreases and the buffer size can be smaller. This can be achieved by a simple alternation of GRA that adds information on starting timing to one of the VP terminating nodes. The result obtained in evaluating GRA-DT in some lattice networks shows that the number of self-healing OAM cells is about 55-86% of that for GRA in the case of double link failures. In addition, GRA-DT effectively reduces the redundant link resource reservation, and thus the restoration ratio was increased by 20% for the 36 node network in the event of node failures.