2 commonly used terms in MPLS are LDP and RSVP-TE. While the former relates to easy provisioning in MPLS setup, the latter i.e. RSVP-TE is related to guarantee bandwidth for traffic communication. LDP setups LSPs based on routing data, whereas RSVP setups additional traffic engineered LSPs.
LDP is abbreviation for Label Distribution Protocol that defines a set of process and messages by which one LSR (Label Switched Router) informs another of the label bindings. LSR further establishes label switched paths through a network by mapping network layer routing information to data-link layer path .In case of MPLS LDP , Label bindings is established automatically for specific FECs (behaviour is different by different vendors).
RSVP-TE is used to establish MPLS transport LSPs for meeting traffic engineering requirements. It is mainly used to provide QoS and load balancing across the network including optical Core network. The RSVP-TE (traffic extension) protocol is an addition to the RSVP protocol with extensions to allow it to set up optical paths in an agile optical network. RSVP is the primary choice if we need to perform Traffic Engineering ie FRR, DiffServ-TE, Explicit Routing etc.
Below table differentiates between MPLS LDP and RSVP(-TE) –