An LSP is not known to be workable until it is actually established by the signaling component. The signaling component, which is responsible for establishing LSP state and distributing labels, relies on a number of extensions to RSVP:
The Explicit Route object allows an RSVP path message to traverse an explicit sequence of routers that is independent of conventional shortest-path IP routing. The explicit route can be either strict or loose.
The Label Request object permits the RSVP path message to request that intermediate routers provide a label binding for the LSP that it is establishing.
The Label object allows RSVP to support the distribution of labels without changing its existing mechanisms. Because the RSVP Resv message follows the reverse path of the RSVP path message, the Label object supports the distribution of labels from downstream nodes to upstream nodes.