Generalized MPLS differs from traditional [[MPLS]]<ref>GMPLS RFC 3945 "1.2. Multiple Types of Switching and Forwarding Hierarchies"</ref> in that it supports multiple types of switching, i.e., the addition of support for TDM, wavelength, and fiber (port) switching. The support for the additional types of switching has driven GMPLS to extend certain base functions of traditional MPLS and, in some cases, to add functionality.
These changes and additions impact basic LSP properties: how labels are requested and communicated, the unidirectional nature of LSPs, how errors are propagated, and information provided for synchronizing the ingress and egress LSRs.
