A signaling protocol performs some crucial functions when a light-path is to be set up, it performs information exchange between nodes, distribute labels, and reserve resource along the path that is to set up. In a GMPLS network the signaling protocols used are RSVP-TE and CR-LDP that may carry within their messages any object specified by the GMPLS architecture. The signaling protocols are responsible for setting up, modifying or tearing down a G-LSP.
An end-to-end path in a optical network have some specific requirements for the signaling function: as small set up latency (due to restoration purposes), support for bidirectional paths, rapid failure detection and notification, and fast and intelligent restoration.
In the RSVP protocol, signaling happens between source and destination nodes, a signaling message may contain information about QoS requirements and label requests for intermediate nodes. In the CR-LDP protocol signaling occurs in a hop-by-hop basis and indicates the route and its required parameters, in each node the required resource is reserved, a label is assigned and a forwarding table is set.
The routing protocol OSPF-TE is used by routing nodes to exchange Link State Advertisement (LSA) messages. The links state messages contain the active channels, the allocated channels, the channels that are reserved for restoration (back-up channels). Allocated channels also have holding and set-up priority parameters that are used to determine is a path set-up may preempt another already established path. The extensions to OSPF enables to inform the type of LSP that can be established in a link, the current unused bandwidth, the maximum size of G-LSP and the administrative groups supported.
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