Dynamic Routing and Wavelength Assignment Scheme for Protection against Node Failure Ying Wang1, Tee Hiang Cheng1,2 and Biswanath Mukherjee3 1School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 2Lightwave Department, Institute for Infocomm Research, Singapore 3 Department of Computer Science, University of California, Davis, California /16

Outline There are few studies on the design of optical networks that could survive single node failures. We design a dynamic RWA scheme that will set up a primary path as well as a node-disjoint shared protection path for each connection. We propose a novel scheme that uses three vectors to convey incomplete information of link state. Finally, we get the experiment results of some criteria.

Introduction Optical network is prone to failures; hence, network survivability is a major concern of network operators. ․ Resiliency is generally achieved by means of Protection and Restoration. In a typical protection scheme against node failure, the primary and backup paths need to be node-disjoint in any intermediate node along their routes. ․ node-disjoint requirement can also protect against a link failure.

Introduction (contd.) Most of the RWA problem studies related to protection and restoration in the optical layer focus on off-line computation. ․ These problems are pertaining to network planning or static provisioning. DLE (Dynamic Lightpath Establishment) ․ The primary and backup paths need to be calculated at the same time and wavelength channels need to be allocated for both paths.

Network Information Scenarios We consider three possible ways in which network status information can be stored and disseminated and the effect on capacity efficiency. ․ Full Information Scenario (FIS) ․ Partial Information Scenario (PIS) ․ No Sharing of Information Scenario (NSIS)

Full Information Scenario (FIS) Having a centralized RWA server that stores all the information about the network and computes the primary and backup paths for any new wavelength demand. ․ scalability problem

Partial Information Scenario (PIS) PIS is to disseminate the network information to every node in the network such that each ingress node can make a RWA decision based on the network information it posses. ․ Only essential network information can be disseminate. ․ Uses three vectors to describe the state of each link. - Wavelength Channel Availability Vector W avi - Backup Wavelength Channel Reservation Vector W res - Conflict Vector C N

No Sharing of Information Scenario (NSIS) When ingress nodes make a routing and wavelength assignment decision, it has no information of existing primary and backup lightpaths, so it cannot share any wavelength channels on the backup lightpath with others; ․ It will result in the worst capacity efficiency and can be used as a benchmark

ILP solution Values given : N Set of nodes in the network E Set of unidirectional fiber links in the network W Set of wavelengths channel on each fiber link s Source node of a lightpath d Destination node of a lightpath S ij w Assume the value of 1 if wavelength channel w is free on link ij; zero otherwise The variables are: P ij w Assume the value of 1 if the primary lightpath uses wavelength channel w on link ij; zero otherwise B ij w Assume the value of 1 if the backup lightpath uses wavelength channel w on link ij; zero otherwise Z ij w The cost of using wavelength channel w on link ij in the backup lightpath

ILP solution (contd.) The ILP formulation is as follows:

ILP solution (contd.)

Experiment Result Capacity Efficiency Effectiveness of PIS with Different Number of Wavelength Channels per Link Capacity Comparison between Node Failure and Link Failure Protection

Capacity Efficiency The saving in the total number of wavelength channels used between NSIS and FIS varies from 18% to 23%, the saving in total wavelength channel usage between NSIS and PIS is from 10% to 15%. The result seems reasonable.

Effectiveness of PIS with Different Number of Wavelength Channels per Link # of wavelength channels per link Saving in total wavelength channel usage between NSIS and PIS 369% ~ 13% 485% ~ 10% 604% ~ 7% 1610%~ 15% The results lead us to conclude that there exists an optimal number of wavelengths to aggregate; beyond which, the network will suffer a significant drop in capacity efficiency.

Capacity Comparison between Node Failure and Link Failure Protection The simulation results also show that for most meshed topologies, less than 7% extra capacity is needed to provide node and link failure protection compared to link failure protection.