To reduce the cost of fault management in the alloptical networks, it is investigated to detect the degradation of optical signal quality solely at the terminal points of all-optical monitoring paths. The monitoring paths must be routed so that all single-link failures can be localized using routes information of monitoring paths where signal quality degradation is detected. However, routes computation for the monitoring paths that satisfy the above condition is time consuming. This paper proposes a procedure for deriving the lower bounds of the required number of monitoring paths to localize all the singlelink failures, and an efficient monitoring path computation method based on the derived lower bounds. The proposed method repeats the route computation for the monitoring paths until feasible routes can be found, while the assumed number of monitoring paths increases starting from the lower bounds. With the proposed method, the minimum number of monitoring paths with the overall shortest routes can quickly be obtained when the possible terminal nodes of monitoring paths are arbitrarily given. Thus, the proposed method can minimize the operational cost of monitoring the degradation of signal quality and can reduce the overhead traffic transferred through the monitoring paths.
In MPLS (Multi-Protocol Label Switching) over optical networks, both the optical level and the MPLS level fault recovery can be considered. Generally, a more flexible path arrangement can be realized by the MPLS level recovery, while fast recovery can be achieved by the optical level recovery. When the optical level recovery is adopted, only normal traffic is carried through the working lightpaths and only recovered traffic is carried through the backup lightpaths. In contrast, the working LSPs (Label-Switched Paths) and the backup LSPs corresponding to other working LSPs can be accommodated into an identical lightpath when the MPLS level recovery is adopted. By such sophisticated accommodation of LSPs into the lightpaths, lightpath bandwidth can be utilized efficiently under the condition that the bandwidth utilization is restricted to attain the given objective of transfer quality for the MPLS packets in the normal state and unrestricted in a short time a failure occurs somewhere in the network. This paper proposes a simple mathematical programming model to obtain the optimum arrangement of the working and backup LSPs assuming the MPLS level recovery and a practical LSPs provisioning mode. By comparing the minimized network cost obtained from the optimum arrangement of the working and backup LSPs with the network cost resulting from the optical level recovery, this paper quantitatively evaluates the effectiveness of such bandwidth utilization improvement obtained from the MPLS level recovery and reveals that the MPLS level recovery can actually reduce the network cost due to its flexible arrangement of LSPs on the lightpaths.Keywords MPLS over optical networks · MPLS level fault recovery · Arrangement of working and backup LSPs · Network cost · Mathematical programming model
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