trol channel is still operational. Control channel failure can result in the transfer of LMP operations to a backup control channel. If no LMP control channel is up, it is impossible to be sure of the state of the data links and LMP cannot collect any further information. The data links are marked as "degraded" and the signaling components can be warned that problems may occur and not be properly rectified. The signaling components could take remedial action such as rerouting the LSPs. 8.6.2 Traffic-Engineering Links There may be a large number of optical fibers between a pair of optical switches. Since it is usually the case that several of these fibers have the same properties as far as routing protocols are concerned-that is, the same endpoints, QoS, and so on-it makes sense not to flood the routing database with duplicated information for each individual fiber. For routing purposes, therefore, fibers with the same properties are grouped together into a traf- fic-engineering link, and only the traffic-engineering link is advertised via routing. However, if individual fibers are not known through routing information, GMPLS LSRs need a way of identifying individual fibers within a traffic- engineering link SO that a signal switched into a fiber by the upstream LSR can be picked up by the downstream one. LMP meets this need by provid- ing mechanisms for Mapping the ID used at one end of an optical fiber to the ID used at its other end (link verification) Grouping sets of IDs at either end into the corresponding traffic- engineering link ID (link summarization) GMPLS in Optical Networks 8.6.3 Link Verification Link verification has two purposes: The verification of data connectivity on particular data links The automatic determination of the mapping between local and remote interface IDs for both data and traffic-engineering links In GMPLS, LSRs use the interface ID mappings determined by LMP link verification to signal exactly which fiber of a traffic-engineering link is the target for an LSP. The link verificati