3.4 Key MPLS TE Features:

Before discussing the signaling component in detail, it;s worth mentioning some of the key MPLS TE features, which are as follows:

1. Explicit routes: MPLS supports setting up of explicit routes, which can be an important tool for load balancing and satisfying other objectives so as to steer traffic away from particular paths. Specific implementation detail about how explicit routes are formed and used will be discussed in next chapter, where RSVP-TE is discussed.

2. Path preemption: Some tunnels are more important than others. Say for example, a VoIP tunnel and data tunnel may compete for same resources, in which case VoIP tunnel is given a higher priority and data tunnel is made to recalculate a path or just drop, if no path is available. Tunnels have 2 priorities: setup priority and hold priority. Each can have a value from 0 to 7 and the higher the priority number the lower the tunnels importance. The setup priority is used when setting up a tunnel and is compared with the hold priority of already established ones. If the setup priority is higher than the hold priority of established tunnel, then established tunnel is preempted.

3. Fast Re-route: In case of a link failure, interior gateway protocols may take of the order of 10 seconds to converge. Fast reroute involves pre-signaling of backup path along with the primary path. The protection may be path protection (end-to-end) or local protection which may be further differentiated into link protection and node protection. Exact fast re-route protection using RSVP-TE is discussed in the next chapter.