Appendix C: Solutions to Selected Study Questions


1. See Section 1.3.1.

2. The two schemes are Label-Inferred LSPs (L-LSPs) and EXP-inferred LSPs (E-LSPs). See Section for more details.

3. See Section

4. See Section

5. Each LER builds one LSP to each of the other LERs. So each LER builds 99 LSPs. As there are 100 LERs, the total number of LSPs in network is 100 × 99, or 9900.

6. See Section 1.3.3.

7. See Figure 1.11 and the associated text.>


1. The Tunnel Id field in the Session Object, uniquely identifying the LSP at the head end is encoded as a 16-bit field. Therefore, the head end can be ingress for up to 16k LSPs only.

2. Many times it is desirable to keep the path within one geographic location in the normal case, but it is acceptable to let it take an out-of-area path following a failure. In such cases, link coloring may place too strict a constraint on the computation. The problem is that if no path is available within the geographic area (e.g. following a failure), link colors will not allow a path that crosses the domain (see also the discussion on fate sharing in Chapter 3). In contrast, IGP metrics could be set up such that the cross-geography links would be given very high metric and used as a last resort.

3. See RFC 5712. The two main ideas behind soft preemption are a) There should be minimum impact to customer traffic. Therefore, the LSPs being preempted should be given a chance to switch to an alternate path in a ...

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