the initiator, would also be useful. In fact, they are useful. In a densely used network, populated mostly with bidirectional (symmetric) and unidirectional forward LSPs, it may not be possible to find a route for a new bidirectional data flow that has enough available resources for both LSP directions. In this scenario, the only solu- tion may be to signal the forward and reverse halves of the desired LSP sep- arately. The resulting combination is known as an asymmetric bidirectional Asymmetric bidirectional LSPs can be set up using any of the pre- GMPLS methods that were used to set up symmetric bidirectional LSPs. In fact, one of the drawbacks of these methods, the difficulty in getting the two directions to follow the same path, is not an issue for asymmetric bidirec- tional LSPs. However, the issue of needing a management and signaling protocol still applies, and the problem of coordinating the forward and reverse halves of the LSP still exists. Reverse-path LSP signaling might also be achieved by reusing the GMPLS support for bidirectional LSPs with the (not yet standardized) understanding that as long as an upstream label is present, the Label Request and Label objects may be omitted from Path and Resv messages, respectively. Given this understanding, an asymmetric bidirectional LSP, with the two LSP directions following different paths, can be set up by Chapter 8 separately signaling the forward and reverse halves of the LSP. Note that practical network administration tools would tie the two halves of the asym- metric LSP together such that they can be managed as a single logical entity. 8.6 Link Management Protocol (LMP) When GMPLS is used to signal LSPs across core optical networks, a num- ber of new management issues arise: If most of the switches in an optical network are photonic, and therefore may not automatically spot loss of light (LoL), how can the precise location of a fault be localized? If the link between two switches consists of a large bundle of optical fibers, how can the routing protocol