The role of TE is to get the traffic from edge to edge in the network in the most optimal way.
- MPLS TE takes into account the configured (static) bandwidth of links.
- MPLS TE takes link attributes into account (for instance, delay, jitter).
- MPLS TE adapts automatically to changing bandwidth and link attributes.
MPLS TE allows for a TE scheme where the head end router of a label switched path (LSP) can calculate the most efficient route through the network toward the tail end router of the LSP. The head end router can do that if it has the topology of the network. Furthermore, the head end router needs to know the remaining bandwidth on all the links of the network. Finally, you need to enable MPLS on the routers so that you can establish LSPs end to end. The fact that label switching is used and not IP forwarding allows for source-based routing instead of IP destination-based routing. That is because MPLS does forwarding in the data plane by matching an incoming label in the label forwarding information base (LFIB) and swapping it with an outgoing label.
Therefore, it is the head end label switching router (LSR) of the LSP that can determine the routing of the labeled packet, after all LSRs agree which labels to use for which LSP.