Technology Overview

Related Concepts

**Table 1** Related concepts
Concept	Description
MPLS TE tunnel	MPLS TE often associates multiple LSPs with a virtual tunnel interface, and such a group of LSPs is called an MPLS TE tunnel. An MPLS TE tunnel is uniquely identified by the following parameters: Tunnel interface: a P2P virtual interface that encapsulates packets. Similar to a loopback interface, a tunnel interface is a logical interface. A tunnel interface name is identified by an interface type and number. The interface type is tunnel. The interface number is expressed in the format of slot ID/card ID/port ID. Tunnel ID: a decimal number that identifies an MPLS TE tunnel and facilitates tunnel planning and management. A tunnel ID must be specified when an MPLS TE tunnel interface is configured. Figure 1 MPLS TE tunnel and LSP A primary LSP with an LSP ID 2 is established along the path LSRA → LSRB → LSRC → LSRD → LSRE on the network shown in Figure 1. A backup LSP with an LSP ID 1024 is established along the path LSRA → LSRF → LSRG → LSRH → LSRE. The two LSPs are in MPLS TE tunnel named Tunnel 1 with a tunnel ID 100.
CR-LSP	LSPs in an MPLS TE tunnel are generally called constraint-based routed label switched paths (CR-LSPs). Unlike Label Distribution Protocol (LDP) LSPs that are established based on routing information, CR-LSPs are established based on bandwidth and path constraints in addition to routing information.

MPLS TE Tunnel Establishment and Application

An MPLS TE tunnel is established using a series of protocol components, as shown in Table 2. They work in sequence during tunnel establishment.

**Table 2** Four MPLS TE components
No.	Name	Description
1	Information advertisement component	In addition to network topology information, TE requires network load information. MPLS TE introduces the information advertisement component by extending an existing IGP, so that TE information can be advertised. TE information includes the maximum link bandwidth, maximum reservable bandwidth, reserved bandwidth, and link colors. Each node collects TE information about all nodes in a local area and generates a traffic engineering database (TEDB).
2	Path calculation component	The path calculation component runs the Constraint Shortest Path First (CSPF) algorithm and uses data in the TEDB to calculate a path that satisfies specific constraints. Evolving from the Shortest Path First (SPF) algorithm, CSPF excludes nodes and links that do not satisfy specific constraints and uses SPF to calculate a path.
3	Path establishment component	The path establishment component establishes the following types of CR-LSPs: Static CR-LSP: Static CR-LSPs are set up by manually configuring forwarding information and resource information, independent of signaling protocols and path calculation. Setting up a static CR-LSP consumes few resources because no MPLS control packets are exchanged between two ends of the CR-LSP. Static CR-LSPs cannot be adjusted dynamically when the network topology changes; therefore, static CR-LSPs generally apply to small-scale networks with simple topologies. Dynamic CR-LSP: Dynamic CR-LSPs are set up by the NetEngine 8000 F using Resource Reservation Protocol-Traffic Engineering (RSVP-TE) signaling information, which can carry constraint parameters, such as the LSP bandwidth, partial explicit routes, and colors. There is no need to manually configure each hop along a dynamic CR-LSP. Dynamic CR-LSPs apply to large-scale networks.
4	Traffic forwarding component	The traffic forwarding component imports traffic to MPLS TE tunnels and forwards the traffic based on MPLS. The preceding three components are enough for setting up an MPLS TE tunnel. However, an MPLS TE tunnel cannot automatically import traffic after being set up. Instead, it requires the traffic forwarding component to import traffic to the tunnel.

An MPLS TE network administrator only needs to configure link attributes based on link resource status and tunnel attributes based on service needs and network planning. MPLS TE can then automatically establish tunnels based on the configurations. After tunnels are set up and traffic import is configured, traffic can then be forwarded along tunnels.