Routing, Wavelength and Time-Slot Assignment in Time Division Multiplexed Wavelength-Routed Optical WDM Networks

This paper studies the routing and wavelength assignment problem for a circuit-switched time division multiplexed (TDM) wavelength-routed (WR) optical WDM network. In a conventional wavelength routed network, an entire wavelength is assigned to a given session (or circuit). This can lead to lower channel utilization when the individual sessions do not need the entire channel bandwidth. This paper considers a TDM-based approach to reduce this inefficiency. In this network architecture, each individual wavelength is partitioned in the time-domain into fixed-length time-slots organized as a TDM frame. 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, the goal is to determine the route, wavelength and time-slot assignment (RWTA) that meets the given request. This is similar to the routing and wavelength assignment problem studied for WR networks. In this paper, we present a family of RWTA algorithms and study the resulting blocking performance. For routing, we use the existing shortest-path routing algorithm with a new link cost function called least resistance weight function (LRW), that incorporates wavelength utilization information. For wavelength assignment, we employ the known least loaded (LL) wavelength selection; and for time-slot allocation, we present the leastloaded time-slot (LLT) algorithm with three different variations. Simulation based analyses are used to compare the proposed TDM architecture to traditional wavelength-routed networks, both with and without wavelength conversion. The goal is to compare the benefits of TDM and wavelength conversion relative to WR networks towards improving performance. The results show that the use of TDM provides substantial gains especially for multi-fiber networks.