Hellstrand et al. They both support explicitly routed label switched paths. 2.2 Explicit merging A recovery scenario is a special case of merging of two LSPs. In a recovery scenario when the traffic is switched over to the recovery path, the primary path does not longer work and hence does not forward any traffic. At the merging point, the PML, there is only one traffic stream that either comes, at normal conditions, on the primary path or, at failure situations, on the recovery path.
Traffic only runs on one path at the same time - either the recovery path or the primary path.
The traffic stream is not doubled on the merged LSP and hence no update of any resource allocation is needed. To allow for this special case an indication is needed to explicitly inform that recovery merge is requested. Also, a flag may be set to indicate compulsorily merge. Hellstrand et al. Reserved Zero on transmission.