Evaluation of routing algorithms for distributed lightpath establishment in wavelength-routed networks

Optical networks, where all-optical wavelength channels (called lightpaths) convey traffic, have been considered to effectively utilize WDM technology. In distributed lightpath networks, each node sets up and tears down the lightpath between a pair of communicating nodes. Therefore, conflicts about wavelength reservations during signaling operations may occur because of a lack of precise link-state information. In this paper, we evaluate effects of delayed link-state information on reservation protocols and routing algorithms through some simulations. More specifically, we evaluated the average path setup time for routing algorithms in distributed networks, and found how the frequency of link-state information exchange affects the precision of collected link-state information. From simulation results, we conclusively confirmed that a backward reservation-protocol lessens the effect delayed link-state information has. The effect is less than 0.2% increase of blocking probability with the backward reservation protocol, while the forward reservation protocol increases the blocking probability more than 15%. We also confirm the proposed alternate routing algorithm shortens lightpath setup time about 20% than the least loaded routing algorithm assuming ideal conditions.