Monish Chatterjee

A survey on regenerator Placement Problem in translucent optical network

Recent research work reveals that the performance of translucent optical network is very near to fully opaque network but much better than transparent network in terms of cost and overall blocking. A translucent optical network is capable to reduce the network design cost as well as routing cost by dividing each light-path into one or limited number of segments by selecting some nodes as regenerator nodes in the network which helps retain the original optical signal quality. Minimization of the total number of placed regenerators and selection of their best locations to establish a path between every pair of source-destination nodes in the network are the main objective of translucent optical network design. This is known as regenerator Placement Problem (RPP) which has been proved to be NP-complete. This paper will provide an overview of various research works and heuristics developed on RPP along with their advantages, drawbacks and performance.

New strategies for static routing and wavelength assignment in de Bruijn WDM networks

Blocking probability has been one of the important parameters for performance analysis in the design of wavelength routed WDM networks. Existing research has proved that the way in which Routing and Wavelength Assignment (RWA) is carried out significantly affects wavelength conversion requirements, which directly affects the blocking performance. In this paper we propose two new static Wavelength Assignment (WA) strategies namely NRNWA (Nearest Request Next Wavelength Assignment) and LDWA (Link Dependent Wavelength Assignment) for WDM networks based on de Bruijn graphs. We compare these proposed strategies with our earlier static RDWA (Ring Dependent Wavelength Assignment) strategy and the well-known FFWA (First Fit Wavelength Assignment) strategy. For request routing, we consider our earlier CRR (Congestion Reduced Routing) and the well-known SRR (Shift Register Routing) algorithms. We combine the various routing and the WA strategies mentioned above in pairs to form eight static RWA strategies and compare the blocking performance of the eight strategies for different de Bruijn graphs. Performance comparison shows that the proposed strategies perform better than the earlier ones.

Congestion optimized routing in unidirectional de Bruijn WDM networks in presence of node faults

In this paper the problem of reducing congestion in WDM networks based on unidirectional de Bruijn graphs has been addressed in the presence of node faults. We propose a polynomial time routing algorithm for reducing congestion and analyze its time complexity. Congestion is defined as the maximum of the number of lightpaths propagating through a link over all links in the network. Congestion optimization is important as it leads to optimization of the load λmax an important parameter of a lightpath request. Results of the algorithm are shown for de Bruijn networks with various sizes of lightpath requests both in the presence and absence of node faults. Finally we evaluate the performance of the algorithm by comparing the results with those from two other strategies, the greedy routing algorithm and the graph search routing algorithm. Comparisons show that the proposed routing algorithm is the best amongst the three both in the presence and absence of node faults.

Channel Assignment in a High-Bandwidth de Bruijn Optical WDM Network

This paper proposes a channel assignment technique in de Bruijn optical wavelength division multiplexed (WDM) networks that can support lightpaths between pair of nodes. Each lightpath uses a channel along each link in its route. The paper provides a polynomial time algorithm that can be used effectively for the proposed channel assignment technique. The load lambdamax of a set of light path requests is the maximum of the number of lightpaths propagating through a link over all links in the network. At least lambdamax wavelengths will be needed to assign channels to the lightpaths. If a network employs full wavelength conversion then lambdamax wavelengths will be sufficient to perform the channel assignment.

Improved algorithms for dynamic routing and wavelength assignment in WDM all-optical mesh networks

Existing research has shown that the mode in which Routing and Wavelength Assignment (RWA) of lightpath requests are carried out can significantly affect resource consumption in optical WDM networks. The increase in resource consumption in turn directly affects the blocking probability for future lightpath requests. The RWA problem in all-optical networks is known to be NP-Complete. In this paper we propose two heuristic dynamic RWA algorithms namely MLBF (Minimum Load Best Fit) and MLF (Minimum Load Fit) for all-optical mesh networks that can solve the RWA problem effectively in polynomial time. Performance comparisons show that the proposed algorithms outperform some earlier well-known strategies.

Dynamic survivable traffic grooming with effective load balancing in WDM all-optical mesh networks

Traffic grooming in WDM optical networks is a scheme for aggregating several low-speed traffic streams from users onto a high-speed lightpath. In such networks, an optical fiber carries a large number of lightpaths and each individual lightpath carries the traffic of a large number of connection requests. So the failure of a single fiber-link, even for a brief period in such networks is a serious event. Thus survivability of user connections is extremely important. Since the problem of survivable traffic grooming in WDM mesh networks is NP-Complete, we propose a polynomial-time heuristic HDSTG (Heuristic Dynamic Survivable Traffic Grooming) that can be effectively used for dynamic traffic grooming in WDM all-optical mesh networks. Our heuristic is designed to provide guaranteed survivability of connection requests for any single link failure. We also propose two strategies, which can be used for effective load balancing to improve dynamic survivable traffic grooming namely TGMHL (Traffic Grooming with Minimized Hops and Load) and TGML (Traffic Grooming with Minimized Load). Performance comparisons demonstrate that the proposed strategies are better for network cost reduction and throughput enhancement as well.

An efficient traffic grooming policy for heterogeneous WDM mesh networks

Traffic grooming in WDM optical networks is a technique for aggregating many low-speed traffic streams from users onto a high-speed lightpath. In this scheme the objective of the network operator determines the grooming policy. Since traffic grooming problem in WDM mesh networks is NP-Complete, we propose a new polynomial-time static traffic grooming policy namely RCG (Reducing Congestion) for heterogeneous WDM mesh networks. RCG is designed for the network operator to reduce congestion on the logical topology. In addition to reducing congestion, RCG also tries to reduce the use of wavelength-links, number of lightpaths and the number of traffic hops on the logical topology to the extent possible. To the best of our knowledge, no other recently proposed grooming policy has addressed the issue of reducing congestion, lightpaths, wavelength-links and traffic hops together in polynomial time for heterogeneous WDM networks. Performance comparisons with some earlier well-known grooming policies reveal that the proposed policy is much better for throughput maximization.

A wavelength assignment algorithm for de Bruijn WDM networks

This paper proposes an offline wavelength assignment technique for de Bruijn (d, k) optical wavelength division multiplexing (WDM) networks having nodal degree d and diameter k that can support lightpaths between pair of nodes. Each lightpath uses a channel (wavelength) along each link in its route. An efficient algorithm is proposed that can be used to assign wavelengths to lightpath requests in O(k|V|) time, where |V| represents the number of nodes of the de Bruijn network and V represents the set of nodes. The proposed algorithm can be efficiently used for wavelength assignment in de Bruijn WDM networks having limited wavelength conversion capabilities. This work shows that de Bruijn graph can be expressed as union of edge-disjoint rings. Wavelengths are assigned for the individual rings in the graph thus resulting in the assignment for the graph itself. Results are shown for a given de Bruijn graph and for an arbitrary request. The proposed algorithm is compared with two other algorithms, which use two other known works of wavelength assignment on ring topology. Comparisons of the time complexity and the type of wavelength conversion required for these algorithms clearly show that the proposed algorithm is a faster and more efficient way of assigning wavelengths.

Heuristic for Routing and Wavelength Assignment in de Bruijn WDM networks based on Graph Decomposition

An important parameter for performance analysis of Routing and Wavelength Assignment (RWA) strategies in WDM networks is blocking probability. Past research has shown that the process in which RWA is carried out significantly affects the wavelength conversion requirements, which in turn affects blocking probability. In this paper we propose a new strategy GDWA (Graph Decomposition based Wavelength Assignment) for static Wavelength Assignment (WA) in a special class of WDM networks which are based on de Bruijn graph. We combine our own request routing strategy LBR (Load Balanced Routing) with the new WA strategy effectively to propose a new static polynomial time RWA heuristic LBGD-RWA (Load Balancing with Graph Decomposition based RWA). We compare the performance of our heuristic with three alternate RWA strategies. Performance comparison reveals that the proposed heuristic gives the best blocking performance.

An online cost-efficient protection scheme for quick recovery in all-optical WDM mesh networks

Since a single fiber carries a huge amount of data in optical WDM networks, a fiber cut even for a brief period is a very serious event. Designing schemes to prevent disruption of user traffic and recovery techniques from failures is thus an important area of research. Since a single fiber cut is the most common type of fault, in this paper we address the problem of protecting all-optical WDM mesh networks from single link failure. Our proposed onlineprotection scheme is an improvement over an existing approach and is not only cost-efficient in terms of network resource consumption but can also provide quick recovery from a link failure. We first provide an ILP formulation for the problem and then propose a heuristic solution iStreams that can provide near-optimal solution in polynomial time. Performance comparisons with some well-known schemes of protection show that our heuristic algorithm can be a better choice for conserving resource while providing quick recovery from a link failure.