(Generalized Multiprotocol Label Switching) In a WDM optical networking system, it is the ability to route a data transmission based on the wavelength of light that carries it. The routing device only analyzes wavelengths (light frequencies) to make its forwarding decision rather than inspecting fields within each packet. GMPLS adds numerous enhancements to MPLS in order to support optical networks. Originally known as Multiprotocol Lambda Switching, the "L" in the acronym MPLS was the Greek lambda. See MPLS, lambda and WDM.