Jeong-dong Ryoo

Enhanced Protection Schemes to Guarantee Consistent Filtering Database in Ethernet Rings

Most of current ring-based Ethernet protection schemes work on a basis of filtering database (FDB) flush operation to guarantee data forwarding on protection switching. However, when a link or node failure occurs in a congested ring network, delayed data frames that have lower priorities than control frames can cause the FDB inconsistency problem that ring nodes build incorrect FDB information. Under this circumstance, some of ring nodes forward data frames in the wrong directions, so that the ring network shows undesirable and unstable performance. In order to resolve this problem, this paper introduces the following three techniques: flush delay timer, purge triggering, and priority setting. Especially, for the priority setting scheme we develop an absorbing Markov chain model for the Ethernet Ring Protection (ERP) protocol defined by G.8032. Then, we theoretically estimate the expected protection time on protection switching underlying the M/M/1/k queue system and also suggest an enhanced priority setting method to guarantee reliable protection switching even in a congested network. Along with our theoretical approach, we additionally evaluate the protection performance with a network simulator to verify our mathematical model. Simulation results show that our analytic model is indeed capable of estimating the expected protection switching time.

An Optimal Ring-Protection-Link Positioning Algorithm in Carrier Ethernet Ring Networks

Ethernet ring protection (ERP), defined in ITU-T recommendation G.8032, is a promising technology to realize the SONET/SDH-grade resilience in carrier Ethernet infrastructures. With its own loop prevention technique to block a link called ring-protection-link (RPL) in an ERP ring, the ERP introduces a new optimization problem named RPL positioning whose objective is to find the optimal RPL location to minimize the required ring capacity for given traffic demands. In this paper, we derive the optimal RPL positioning as an integer linear programming (ILP) problem and additionally propose an optimal RPL positioning algorithm for more effective ring loading. By evaluations, we demonstrate that our proposed algorithm is indeed capable of finding the optimal RPL equal to the results by an exhaustive search emerged in prior works or the formulated ILP model. But, it is more efficient in computing time than the exhaustive search and the ILP model.

Effective fault management for hierarchical OTN multiplexing using tandem connection monitoring coordinates

We propose and verify fault management method using tandem connection monitoring for OTN multiplexing hierarchy through experiments on fiber-cut event. Marking defects on TCM coordinates that consists of TCM levels and ODU trails, and identifying a root-cause of faults using two consequent actions of trail signal fail and server signal fail are newly presented as means to find fault-originators and root-causes. By effectively managing multiple faults all over the network and all over the hierarchical OTN layers, the fault management method could contribute toward the enhanced OAM for fast end-to-end service maintenance and fast restoration.