 LSR would likely use on the segment of the LSP that links the two LSRs. The receiving LSR processes the path as follows: Chapter 8 Figure 8-2 Label suggestion. Path (Suggested Label = 1a) Path (Suggested Label = 1b) Resv (Label = 1d) Resv (Label = 1c) It selects a label for use on the upstream link (xd). This should be the suggested label (ad=xa) if possible, but it can be any other label. It selects a preferred label for use on the downstream link (Ab). Depending on the properties of the switch, this may be the same value as selected for the upstream interface (ad=xb), for example, if the switch is not capable of wavelength modification. It sends a command to the switch fabric to begin programming the switch (adXXb). It sends a Path message downstream containing the label that it would likely use on the downstream segment (Ab). At some point, it receives a Resv from the downstream LSR. This indicates the actual label to use on the downstream segment (Ac). If the actual label is different from the suggested label (Ac#)b), the switch must Possibly pick a new value for the upstream label (xd). This is necessary if the switch is not capable of wavelength conversion; it would therefore choose the same label as provided from downstream (Ad=1c#1a). Send a command to the switch fabric to program the crossconnect (AdXXc). Wait for the switch to be fully programmed and stable. Send a command to the switch fabric to deprogram the speculative crossconnect (adx)b) as a background event. If the label is the label suggested (Ac=Ab), then no further programming is required, but the LSR must make sure that the programming request made earlier has completed satisfactorily. Finally, the LSR sends a Resv upstream indicating the actual label to use on the link (xd). GMPLS in Optical Networks If everything has worked well and wavelength conversion is not possible, the suggested label from the original message is used on all messages If there are any problems (for example, an actual label is unacceptable), the LSP is torn using the n