Ashok Jhunjhunwala

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.

In this paper, we have proposed an analytical model that computes the blocking probability and the channel utilisation for a given load on the optical networks with wavelength conversion at the nodes. The computation has been carried out for fixed routing with uniform traffic distribution (UTD). When any link on a route blocks a call, the dropped call reduces the offered load on all other links invovled in the route. The overall blocking probability of the network is estimated using Erlang fixed point approximation with the reduced load on the links. The expression has been validated by comparing the results with that of simulation for a number of standard networks including 14 node NSFNET, 20 node ARPANET and 20 node INDIANET. We show that the analytical method performs well in the desired range of blocking probabilities and is applicable to any network topology. © 2008 by the IETE.

In this paper, we consider the problem of maximizing the time of first lightpath request rejection, T in the circuit-switched time division multiplexed (TDM) wavelength-routed (WR) optical WDM networks. TDM is incorporated into WDM, to increase the channel utilization when the carried traffic does not require the entire channel bandwidth. In TDM-WDM network, multiple sessions are multiplexed on each wavelength by assigning a sub-set of the TDM slots to each session. Thus, given a session request with a specified bandwidth, a lightpath has to be established by using the routing, wavelength and time-slot assignment (RWTA) algorithms. If the lightpath cannot be established, lightpath request rejection or call blocking occurs. As each lightpath is substantial revenue and long-lived, lightpath request rejection is highly unfavourable in the opitcal backbone networks. In this paper, we are proposing an intelligent routing, wavelength and time-slot reassignment algorithm for multi rate traffic demands, where, when a call gets blocked, the already established calls in the network are rerouted, wavelength and timeslot reassigned so as to accomodate the blocked call. Since we are talking of slow arrivals and long holding times for the lightpaths, it is possible to do this reassignment while provisioning a new call. Simulation based analyses are used to study the performance of the proposed reassignment algorithm. The results show that the proposed reassignment algorithm can be used to maximize the time of first call blocking, thereby accommodating more calls in the network before upgrading the network capacity. © 2006 IEEE.

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.

In this paper, we have proposed an analytical model for optical networks with full wavelength conversion at the nodes. We have derived an analytical expression to compute the carried traffic on links of the network for fixed routing with uniform traffic distribution (UTD). The carried traffic on a link in the network is thinned proportionately based on the blocking probability of the other links on the route. The blocking probability of the network is estimated using Erlang fixed point approximation with the reduced load on the links. The channel utilisation at a particular load is derived using the blocking probability. Thus the analytical model gives an estimate of the blocking probability and the channel utilisation at any given load and is applicable to any network topology. We have computed the carried traffic for a few example networks, such as 14 node NSFNET, 20 node ARPANET and 20 node INDIANET and validated the analytical results with simulations. We show that the analytical method performs well in the desired range of blocking probabilities and it is computationally efficient. © 2007 IEEE.

We present an analytical tool to enhance the blocking performance in the circuit-switched wide-area optical wavelength division multiplexed (WDM) networks with no wavelength conversion at the nodes. Given any network of arbitrary topology, the aim is to see if one can achieve the wavelength conversion (optimal) performance by using wavelength reassignment techniques in no conversion networks. If there is significant performance deviation, the tool identifies the critical points in the network which prevents the reassignment to totally remove wavelength continuity constraint (wcc) blocking. Once the critical points are identified, the tool appropriately modifies the routing such that the wavelength reassignment can achieve the optimal performance. © 2007 IEEE.

In this paper, we consider the problem of maximizing the time of first lightpath request rejection, T in the circuit-switched time division multiplexed (TDM) wavelength-routed (WR) optical WDM networks. TDM is incorporated into WDM, to increase the channel utilization when the carried traffic does not require the entire channel bandwidth. In TDM-WDM network, multiple sessions are multiplexed on each wavelength by assigning a sub-set of the TDM slots to each session. Thus, given a session request with a specified bandwidth, a lightpath has to be established by using the routing, wavelength and time-slot assignment (RWTA) algorithms. If the lightpath cannot be established, lightpath request rejection or call blocking occurs. As each lightpath is substantial revenue and long-lived, lightpath request rejection is highly unfavourable in the optical backbone networks. In this paper, we are proposing an intelligent routing, wavelength and time-slot reassignment algorithm for multi-rate traffic demands, where, when a call gets blocked, the already established calls in the network are rerouted, wavelength and time-slot reassigned so as to accommodate the blocked call. Since we are talking of slow arrivals and long holding times for the lightpaths, it is possible to do this reassignment while provisioning a new call. Simulation based analyses are used to study the performance of the proposed reassignment algorithm. The results show that the proposed reassignment algorithm can be used to maximize the time of first call blocking, thereby accommodating more calls in the network before upgrading the network capacity. © 2007 Elsevier B.V. All rights reserved.

In this paper, we identify the topological and routing technique constraints on the performance of optical backbone WDM networks with wavelength conversion at the nodes and propose techniques to overcome this constraints so that the network performance is enhanced. For any session request, a lightpath has to be established on the shortest path between the node pairs. As each lightpath is a substantial revenue and long-lived, the network operator would like no lightpath request rejection (call blocking) or would like to accomodate more calls in the network before he has to upgrade his network. Hence given a network, we are proposing an analytical method to identify the critical links of the network which will cause early blocking, for the fixed shortest path routing. Once the critical links are identified, we would like to analyse the physical location of these critical links on the network topology and propose a new fixed routing technique namely, restricted routing by which the performance is enhanced as it balances the load uniformly among the links. In this routing technique, not all the calls have the shortest path. We compare the performance of the restricted routing with the optimal performance where all the links have equal blocking probability. The analysis is carried out on some of the standard backbone networks and the results show that by the restricted routing there is a significant performance improvement. ©2008 IEEE.