MPLS-Enabled Applications: Emerging Developments and New Technologies

2.8. OFFLINE PATH COMPUTATION

Traffic engineering with RSVP-TE relies on explicit paths. Most of the discussion so far focused on a model where the paths are computed dynamically by the routers. As seen in previous sections, the results of this computation may not be the most optimal. Offline computation tools are used to provide better results. This model is particularly familiar to operators from an ATM PVC (permanent virtual channel) background.

Offline computation tools provide the following advantages in the context of traffic engineering:

1. Exact control of where the paths are placed. The operator knows where the traffic is going to flow. There are no surprises from dynamic computation.

2. Global view of the reservations and of the bandwidth availability. As seen in Section 2.4.3, this global knowledge enables optimal placement of the LSPs.

3. Ability to cross area and AS boundaries. The computation is not based solely on the information in the TED; therefore, the restriction to a single IGP area does not apply.^[]

   ^[] This assumes that the TE information for the other area/AS is available through some other means.

4. Computation can take into account both the normal and the failure cases. One of the biggest strengths of offline tools is that they can take into account the impact of one or more link failures when computing the optimal placement of LSPs. Doing so can ensure that LSPs will always be able to reroute following a failure. Figure 2.5 shows an example of such a scenario. Assume ...