Actually, they are very complementary technologies and often offer similar results in terms of reducing networking OPEX costs. ROADM technology is hardware based, while GMPLS is a draft standard for network control, and is software based. They are both elements of an optical network architecture.
ROADM was created in an effort to ease the planning and provisioning process of circuits on a WDM ring. This replaced what was once a very manual process with little room for error with flexibility to make changes on the fly, thus leaving room for network re-configuration as networks and customer requirements changed. Some ROADM technologies can even be extended beyond use in rings, and can be applied to mesh networks. The distinguishing feature of the ROADM is that switching is done in the optical domain, without converting the signal back to an electronic form.
GMPLS on the other hand was designed to automate the provisioning and traffic management across optical networks, somewhat similar to what MPLS offered to data networks. In the case of GMPLS, the standards are being defined by the IETF (Internet Engineering Task Force). The ITU (International Telecommunications Union) has extended these concepts in formulating the G.ASON standards, taking into account additional requirements important to service providers. The Optical Internetworking Forum (OIF) formulates interoperability agreements based primarily on the G.ASON standards. Most recently the OIF User to Network Interface 2.0 (OIF UNI 2.0) has been demonstrated at Supercomm to automatically provision Ethernet circuits across a multi-vendor optical network..
GMPLS and G.ASON, although applicable in principle to ROADM-based networks, are now practically limited to networks where switching is done electrically. The problem of choosing a route in an all-optical network can be a complex optical engineering task, a problem that the standards groups have not yet tackled. In this case a UNI approach is ideal, as it can be used for interoperable automated provisioning while leaving the tough routing decision to a technology-aware software module in the optical network.
