In all-optical WDM networks, splitters at branch nodes are used to realize multicast trees. It is expensive to place splitters at all of the nodes in an all-optical WDM network. To reduce the cost, splitters can be placed at a subset of nodes. The problem of selecting a subset of nodes to place the splitters such that certain performance measure is optimized is called the splitter placement problem. Splitter placement problems in all-optical WDM networks in which a single light tree is constructed to realize each multicast connection have been studied in previous researches. This paper studies the splitter placement problem in all-optical WDM networks in which a light forest consisting of a collection of light trees is used to realize a multicast connection. The goal is to place a given number of splitters in the network such that the average per link wavelength resource usage of multicast connections is minimized. An upper bound and a lower bound on the per link average wavelength resource usage for a given number of multicast connections are derived. Two splitter placement methods are proposed for this problem. The two proposed splitter methods are shown to yield significant lower average wavelength resource usage than the random placement method. One of the methods is shown to produce near minimum average wavelength resource usage.
