Re-routing at critical nodes to enhance performance of wavelength reassignment in all-optical WDM networks without wavelength conversion
Reassignment of calls to different wavelengths on blocking can be used in WDM networks without wavelength conversion to get almost the same performance as that of WDM networks with wavelength conversion for circuit switched traffic [11]. However, in a few networks, we did find that while the reassignment on blocking does improve the performance of WDM networks without wavelength conversion, the performance falls short of that of wavelength conversion networks. In this paper, we analyze the reasons for this behavior in these networks. On identifying certain critical nodes as a cause of this behavior, we propose a rerouting technique around the critical node. With a small amount of rerouting, this bottleneck can be removed and the performance of WDM networks without wavelength conversion becomes almost equal to that of networks with wavelength conversion, thus making the wavelength conversion (costly) feature, as redundant. In this paper, we also propose a technique to carry out seamless wavelength reassignment so as not to disrupt traffic during the wavelength reassignment process. © 2008 IEEE.
Wavelength reassignment algorithms for all-optical WDM backbone networks
In this paper, we consider the problem of enhancing the blocking performance, in the circuit-switched wide-area optical wavelength-division multiplexed (WDM) networks with no wavelength conversion at the nodes. The limitation of such a no conversion network is the wavelength continuity constraint (wcc) which requires the same wavelength on all the hops of the path. Whenever there is a session request, a lightpath has to be established in the network. If the lightpath could not be established, lightpath request rejection or call blocking occurs. As each lightpath is a substantial revenue and is long-lived, lightpath request rejection is highly unfavorable in the optical backbone networks. An optimal optical network is the one with wavelength conversion capability at the nodes. In these conversion networks, blocking occurs due to capacity exhaustion on the links and not due to wcc. Hence these networks have the lowest possible blocking probability (Pb) achievable for any given network. Our aim is to see if one can achieve this near optimal blocking performance in no conversion networks by using our proposed wavelength reassignment algorithms. In the reassignment technique, when the new call gets blocked due to wcc, the already established calls or lightpaths are wavelength reassigned, so as to create a wavelength-continuous route in order to accommodate the new call. During wavelength reassignment, the routes for all the calls remain the same, i.e. no rerouting is done. We have proposed two heuristic reassignment algorithms namely, MOLC and Random and have studied their performance on some standard backbone optical networks. Simulation results show that in these example networks, our proposed reassignment algorithm can mostly remove the blocking due to the wcc and can achieve the wavelength conversion performance. © 2007 Elsevier B.V. All rights reserved.