Carriers are seeking to gain efficiencies and develop advanced services by merging the worlds of IP and optical networking. However, first they need to overcome the extremely complex multilayer architecture that's been cobbled together to carry IP service over networks designed to support voice and fixed circuits. Ultimately, they need one control plane that extends from IP at Layer 3 right down to the optical transport level at Layer 1.

Generalized Multi-protocol Label Switching (GMPLS) aims to meet this need by extending network intelligence from the network edge through the core and back to the edge under a unified control plane.

A proposed IETF standard, GMPLS is still in development and isn't expected to be ready for wide-scale deployment for 1 to 2 years. But the technology isn't entirely new, because it builds on many of the gains that came through the development and standardization of Multi-protocol Label Switching (MPLS ), which has simplified network architecture by replacing the need for ATM and frame relay equipment to oversee traffic engineering.

MPLS improves IP scalability and quality of service by creating virtual label-switched paths (LSP) across a network of label switching routers (LSR ). GMPLS' primary enhancement to MPLS is its capability to establish connections at Layer 1.

GMPLS can be deployed in two ways: overlay model or peer model. In an overlay model, also called a UNI, the router is a client to the optical domain and interacts only with the directly adjacent optical node. In the overlay model, the actual physical light path is decided by the optical network and not by the router.

In the peer model, the IP/MPLS layer operates as a full peer of the optical transmission layer. Specifically, the IP routers are able to determine the entire path of the connection, including through the optical devices.

The aim of GMPLS - both peer and overlay models - is to extends the reach of MPLS from routers through to the optical domain, where forwarding decisions are based on time slots, wavelengths or physical ports (called "implicit labels" in GMPLS terminology), not packet boundaries. GMPLS enables such cross-domain peering by supporting new classes of LSRs, including dense wavelength division multiplexers, add/drop multiplexers and optical cross-connects.