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NE20E-S2 V800R010C10SPC500 Feature Description - MPLS 01

This is NE20E-S2 V800R010C10SPC500 Feature Description - MPLS
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Associated Bidirectional CR-LSPs

Associated Bidirectional CR-LSPs

Associated bidirectional CR-LSPs provide bandwidth protection for bidirectional services. Bidirectional switching can be performed for associated bidirectional CR-LSPs if faults occur.


MPLS networks face the following challenges:
  • Traffic congestion: RSVP-TE tunnels are unidirectional. The ingress forwards services to the egress along an RSVP-TE tunnel. The egress forwards services to the ingress over IP routes. As a result, the services may be congested because IP links do not reserve bandwidth for these services.

  • Traffic interruptions: Two MPLS TE tunnels in opposite directions are established between the ingress and egress. If a fault occurs on an MPLS TE tunnel, a traffic switchover can only be performed for the faulty tunnel, but not for the reverse tunnel. As a result, traffic is interrupted.

A forward CR-LSP and a reverse CR-LSP between two nodes are established. Each CR-LSP is bound to the ingress of its reverse CR-LSP. The two CR-LSPs then form an associated bidirectional CR-LSP. The associated bidirectional CR-LSP is mainly used to prevent traffic congestion. If a fault occurs on one end, the other end is notified of the fault so that both ends trigger traffic switchovers, which traffic transmission is uninterrupted.


Figure 4-47 illustrates an associated bidirectional CR-LSP that consists of Tunnel1 and Tunnel2. The implementation of the associated bidirectional CR-LSP is as follows:
  • MPLS TE Tunnel1 and Tunnel2 are established using RSVP-TE signaling or manually.

  • The tunnel ID and ingress LSR ID of the reverse CR-LSP are specified on each tunnel interface so that the forward and reverse CR-LSPs are bound to each other. For example, in Figure 4-47, set the reverse tunnel ID to 200 and ingress LSR ID to on Tunnel1 so the reverse tunnel is bound to Tunnel1.


    The ingress LSR ID of the reverse CR-LSP is the same as the egress LSR ID of the forward CR-LSP.

  • Penultimate hop popping (PHP) is not supported on associated bidirectional CR-LSPs.

    The forward and reverse CR-LSPs can be established over the same path or over different paths. Establishing the forward and reverse CR-LSPs over the same path is recommended to implement the consistent delay time.

Figure 4-47 Associated bidirectional CR-LSP

Usage Scenario

  • An associated bidirectional static CR-LSP transmits services and returned OAM PDUs on MPLS networks.

  • An associated bidirectional dynamic CRLSP is used on an RSVP-TE network when bit-error-triggered switching is used.

Updated: 2019-01-02

Document ID: EDOC1100055471

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