Downgrading the CT of Bandwidth Sharing LSP Paths

Consider a link configured with two class types CT0 and CT1 and making use of the RDM admission control model as shown in Figure 1.

Figure 1. Sharing bandwidth when an LSP primary path is downgraded to backup CT

Consider an LSP path Z occupying bandwidth B at CT1. BC0 being the sum of all CTs below it, the bandwidth occupied in CT1 is guaranteed to be available in CT0. When new path X of the same LSP for CT0 is setup, it uses the same bandwidth B as used by path Z as shown in Figure 1 (a). When path Z is torn down the same bandwidth now occupies CT0 as shown in Figure 1 (b). Even if there were no new BW available in CT0 as can be seen in Figure 1 (c), path X can always share the bandwidth with path Z.

CSPF at the head-end node and CAC at the transit LSR node shares bandwidth of an existing path when its CT is downgraded in the new path of the same LSP.