Taehan Lee

Optimal routing and wavelength assignment in WDM ring networks

We consider the routing and wavelength assignment (RWA) problem on WDM ring networks without wavelength conversion. When the physical network and required connections are given, RWA is the problem to select a suitable path and wavelength among the many possible choices for each connection such that no two paths using the same wavelength pass through the same link. We give an integer programming formulation of the problem and propose an algorithm to solve it. Although the formulation has exponentially many variables, we solve the linear programming relaxation of it by using the column generation technique. We solve the column generation problem efficiently by decomposing the problem into several subproblems. After solving the linear programming relaxation, we apply the branch-and-price procedure to get an optimal solution. We test the proposed algorithm on some randomly generated data. Test results show that the algorithm gives optimal solutions to almost all instances under the given node limit of the branch-and-bound tree.

An integer programming approach to the time slot assignment problem in SS/TDMA systems with intersatellite links

Abstract We consider the time slot assignment problem (TSAP) in a cluster of satellite-switched time-division multiple-access (SS/TDMA) satellite system with intersatellite links (ISL). The problem is known to be NP-complete. In this paper, we consider TSAP as a graph coloring problem on a bipartite multigraph which is constructed from the traffic requirements. We give an integer programming (IP) model for TSAP and propose an algorithm based on the column generation technique. Computational results using randomly generated data are reported.

Optimal Multicast Routing and Wavelength Assignment on WDM Ring Networks Without Wavelength Conversion

We consider the multicast routing and wavelength assignment (MC-RWA) problem on WDM bidirectional ring networks without wavelength conversion. We give an integer programming formulation of the problem and propose an algorithm to solve it optimally. The algorithm is based on column generation and branch-and-price. We test the proposed algorithm on randomly generated data and the test results show that the algorithm gives optimal solutions to all of the test problems.

Comparison of routing methods in optical multicast WDM ring networks

Multicast routing and wavelength assignment (MC-RWA) is an important issue when designing multicast WDM ring networks. Two heuristic multicast routing methods, minimum spanning tree (MST) and shortest path routing (SPT), have been studied extensively. However, the comparison of those two heuristics in terms of the number of required wavelengths is still an open issue because of the lack of efficient optimization methods for MC-RWA. In this paper, using a recently developed optimization algorithm, we compare the two multicast routing methods and optimal MC-RWA. The results show that SPT requires about 1–12% more wavelengths than MST. Moreover, the number of required wavelengths under MST routing is shown to be very close to that of the optimal solution.

Exact Modeling and Performance Analysis of Paging Schemes Using Paging Agents

This study considers paging schemes that can page some cells or only one cell within the location area to reduce paging cost by using PAs (Paging Agents) and compares their performances by using a new analytic method. There are three ways of paging schemes using PAs; BSPA (Base Staton Paging Agent), 2SPA (2-Step Paging Agent), LAPA (Location Area Paging Agent). This study proposes exact performance of BSPA and 2SPA using a new analytic method based on Markov chain modeling to find the most efficient paging scheme. Numerical results for various circumstances are presented by using proposed analytic method to select a proper paging scheme in mobile communication networks.

Comparison of wavelength requirements between two wavelength assignment methods in survivable WDM networks

We consider the routing and wavelength assignment (RWA) in survivable WDM network. A path protection scheme assumed and two different wavelength assignment methods for protection paths are considered. Integer programming formulations of RWA under two wavelength assignment methods are proposed and we devised algorithms to solve them. Test results show that the difference of wavelength requirements between two wavelength assignment methods is 5–30–