ABSTRACT
Recall from chapter 5 that the Multi-Protocol Label Switching with traffic engineering extensions (MPLS-TE) operation is composed of four main processes:
Information distribution: This process requires the awareness of available network resources. This “resource-aware” mechanism is implemented by defining relatively simple TE extensions to the traditional topology-driven interior gateway protocols (IGPs) (for example, open shortest path first (OSPF) and integrated intermediate system to intermediate system (ISIS)) so that additional network link attributes such as TE metric, maximum bandwidth, maximum reservable bandwidth, unreserved bandwidth, and administrative group (also known as resource class or link color) are included as part of each router’s link-state advertisement (LSA).
Path selection: This process uses information such as link attributes and topology-state information distributed by the IGP LSAs together with the manually configured constraints (such as path bandwidth and link color) defined at the ingress to select a constrained shortest path that fulfills the specific requirements of traffic trunks. This constraint-based path can be defined administratively offline by a network operator, or it can be computed automatically online by a constraint-based path selection algorithm, for instance, using constrained shortest path first (CSPF).
Path setup: This process requires a signaling protocol to establish a label switched path (LSP) for traffic trunks along the constraint-based path or explicit route that was dynamically determined or 74manually configured earlier in the path selection process. The signaling protocol of interest is the Resource Reservation Protocol with TE extensions (RSVP-TE). These extensions are the primary focus of this chapter. RSVP-TE is the most commonly used signaling protocol in MPLS-TE applications. The other alternative is CR-LDP (constraint-based LSP setup using Label Distribution Protocol [RFC3212]), which is beyond the scope of this book. At present there is no consensus on which protocol is technically better. Service providers should therefore make a choice between the two based on their requirements and networking environments. The traffic trunk attributes discussed previously in chapter 4 are mostly found in RSVP-TE.
Forwarding of traffic across the established LSP.
