However, if multiple failures occur simultaneously, there may not be sufficient remaining capacity to support the offered traffic load. This results in congestion and possibly* packet drops. To improve upon this, traffic engineering (TE) was implemented to make the routing of tunnels sensitive to the offered traffic demand and the available capacity in the network. The routing pro- tocol and RSVP-TE are expanded to advertise not only topology, metric, and link state but also the capacity of a link and the actual measured user traffic on the link. This information is distributed among all core nodes and they use this knowledge to route their tunnels on the lowest-latency path that has sufficient available bandwidth to support the needs of the tunnel. This is referred to as Constrained Shortest Path First (CSPF) routing in contrast to the open shortest path (open meaning simply that all links on the path have their link state up). Because all head-end nodes are acting independently, it is possible that a head end could sig- nal to set up a tunnel only to find that the resources have been grabbed by another head end. The RSVP protocol reserves the resources on each node as the setup message propagates along the path. The signaling message indicates the required bandwidth for this tunnel and each node keeps a record of the resources it has committed and reserved on each of its links. If the signaling mes- sage reaches the tail-end successfully meaning it has been able to reserve resources at each hop, the response messages back to the head end commit the resources to this tunnel. If at any point a node is unable to support the request because it has exhausted the capacity of a required link, it rejects the Routers have buffers that are able to temporarily hold data when the short-term traffic demand exceeds the bandwidth of an outgoing interface. This results in queuing delays but not loss. If the load is sustained, eventually buffers will be over- run and packets will be dropped. This can be partially mitigated by h