I am trying to understand the applicability of MPLS TE in a SP cloud
I understand that a head-end router and a tail-end router will be the MPLS TE tunnel source and destination, and that the LSP path that is created for a specific TE flow can either be a product of dynamic negotiation with the IGP leveraging its TE extensions to pass resource data -- or it can be a product of an explicity configured LSP.
The dynamically created LSP may not necessarily be the "shortest" path, or better stated, the least cost path, because a bandwidth requirement for the TE tunnel may be higher than any particular link -- or set of links and interfaces -- in the "shortest" path can deliver. So, the LSP for MPLS TE can be a suboptimal path through the SP IGP cloud. Optimal paths can be congested, so it is useful to utilize the avilablity of less optimal paths.
Now that I am done rambling, what I dont understand is exactly how MPLS TE tunnels are leveraged in practical situations.
From my experience and knowledge of RSVP in a QoS environment, it is the application that will request resources from the network from each router in the path. In an MPLS TE environment, who is making the demand?
I think its the head-end router itself, but WHEN will it trigger a TE request and on behalf of whom? Unlike a QoS application for RSVP, I dont think the purpose of MPLS TE in an SP cloud is used by the SP for the same purpose.
Can someone with MPLS TE experience provide some of their thoughts on this topic?