The recent emergence of wavelength-division multiplexing technology has led to a tremendous increase in the available transmission capacity in wide area networks. Consequently, these networks may no longer be limited by transmission bandwidth, but rather by the processing capability of electronic switches, routers, and multiplexers in the network. This realization has led to a new wave of research aimed at overcoming the electronic bottleneck by providing optical bypass at the WDM layer. Traffic grooming can be used as a bypass mechanism by which low-rate circuits are assigned to wavelengths in order to minimize the amount of electronic multiplexing equipment. Recently, this topic has received a significant amount of attention in both the research and commercial arenas. In this article we give an overview of the traffic grooming problem and survey some representative work in this area. While most recent work has focused on grooming in SONET rings, grooming traffic in general mesh networks is an important emerging problem.

In this paper we consider circuit assignment algorithms for dynamic traffic in unidirectional WDM/SONET ring networks. Our objective is to minimize the cost of electronic Add/Drop Multiplexers (ADMs) in the network, while being able to support any offered traffic matrix in a rearrangeably non-blocking manner. The only restriction on the offered traffic is a constraint on the number of circuits a node may source at any given time. We provide a lower bound on the number of ADMs required and give conditions that a network must satisfy in order for it to support the desired set of traffic patterns. Circuit assignment and ADM placement algorithms that perform closely to this lower bound are provided. These algorithms are shown to reduce the electronic costs of a network by over 30%. Finally, we discuss extensions of this work for supporting dynamic traffic in a wide sense or strict sense non-blocking manner as well as the benefits of using a hub node and tunable transceivers. I.

Abstract—In this paper, we study the benefits of using tunable transceivers for reducing the required number of electronic ports in wavelength-division-multiplexing/time-division multiplexing optical networks. We show that such transceivers can be used to efficiently “groom ” subwavelength traffic in the optical domain and so can significantly reduce the amount of terminal equipment needed compared with the fixed-tuned case. Formulations for this “tunable grooming ” problem are provided, where the objective is to schedule transceivers so as to minimize the required number of ports needed for a given traffic demand. We establish a relationship between this problem and edge colorings of graphs which are determined by the offered traffic. Using this relationship, we show that, in general, this problem is NP-complete, but we are able to efficiently solve it for many cases of interest. When the number of wavelengths in the network is not limited, each node is shown to only require the minimum number of transceivers (i.e., no more transceivers than the amount of traffic that it generates). This holds regardless of the network topology or traffic pattern. When the number of wavelengths is limited, an analogous result is shown for both uniform and hub traffic in a ring. We then develop a heuristic algorithm for general traffic that uses nearly the minimum number of transceivers. In most cases, tunable transceivers are shown to reduce the number of ports per node by as much as 60%. We also consider the case where traffic can dynamically change among an allowable set of traffic demands. Tunability is again shown to significantly reduce the port requirement for a nonblocking ring, both with and without rearrangements. Index Terms—Graph coloring, integer linear programming (ILP), optical networks, traffic grooming, wavelength-division multiplexing (WDM). I.

Abstract — In this paper, we study the benefits of using tunable transceivers for reducing the required number of electronic ports in WDM/TDM networks. We show that such transceivers can be used to efficiently “groom ” sub-wavelength traffic in the optical domain and so can significantly reduce the number of electronic ports compared to the fixed tuned case. We provide a new formulation for this “tunable grooming ” problem. We show that in general this problem is NP-complete, but we are able to efficiently solve it for many cases of interest. When the number of wavelengths in the network is not limited, we show that each node only needs the minimum number of transceivers (i.e., no more transceivers than the amount of traffic that it generates). This holds regardless of the network topology or traffic pattern. When the number of wavelengths is limited, we show an analogous result for both uniform and hub traffic in a ring. We also develop a heuristic algorithm for general traffic that uses nearly the minimum number of transceivers. In most cases, tunable transceivers are shown to reduce the number of ports per node by as much as 60%. I.