8-1. Suppose LSR C can only generate wavelengths from a range R. Therefore, it signals a label set of "anything in range R except red." LSR D modifies this and signals "anything in range R except red or blue." LSR E forwards this unchanged, and LSR G can select a color that will be acceptable to all of the LSRs in the path, if one is available. Note that the color is not guaranteed to be acceptable. If LSR G chooses, say, green, another LSP B-D-C using green may have been set up while LSR D was waiting for the signaling response from LSR E. This risk can be reduced by also using suggested labels-see the section titled "Suggested Label." 8.2.2 Explicit Label Control GMPLS also introduces explicit label control. This enhances the MPLS con- cept of an explicit route by enabling the ingress LSR to specify the label(s) to use on one, some, or all of the explicitly routed links for the forward and/or reverse path. This is useful, for example, when the ingress LSR wants to insist that the wavelength used is the same along the whole LSP. This might be desirable in order to avoid distortion of the optical signal. It may also be useful in traffic engineering where the path computation engine has knowledge of the labels in use in the network and the switching capabilities of the LSRs. In this case, the path can be computed to include the specific labels to be used at each hop. Explicit labels are specified by the ingress LSR as part of the explicit route. At each LSR along the path, any explicit label that is specified in the explicit route for the next hop is removed and converted into a Label Set object, containing a single label, for the next hop. The LSR that receives this label is then required to use it for that hop and must fail the setup if that label is not locally available. Chapter 8 8.2.3 Egress Label Control When a network administrator initiates the setup on an LSP, he or she is free to specify more or less strictly the path that the LSP should follow and, optionally, as described in the previous subsection, t