Basic Concepts

An MPLS-TP network consists of the section, LSP, and PW layers in bottom-up order. A lower layer is a server layer, and an upper layer is a client layer. For example, the section layer is the LSP layer's server layer, and the LSP layer is the section layer's client layer.

On the MPLS-TP network shown in Figure 1, MPLS-TP OAM detects and locates faults in the section, LSP, and PW layers. Table 1 describes MPLS-TP OAM components.

Figure 1 MPLS-TP OAM application
Table 1 MPLS-TP OAM components

Name

Description

Example

Maintenance entity (ME)

All MPLS-TP OAM functions are performed on MEs. Each ME consists of two maintenance entity group end points (MEPs) and maintenance entity group intermediate points (MIPs) on the link between the two MEPs.
  • Section layer:

    Each pair of adjacent LSRs forms an ME.

  • LSP layer:

    LSRs A, B, C, and D form an ME.

    LSRs D and E form an ME.

    LSRs E, F, and G form an ME.

  • PW layer:

    LSRs A, D, E, and G form an ME.

Maintenance entity group (MEG)
A MEG is comprised of one or more MEs that are created for a transport link. MEGs for various services contain different MEs:
  • A MEG for a P2P unidirectional path contains only one ME.
  • A MEG for a P2P bidirectional path contains two MEs. A MEG for P2P bidirectional co-routed path contains a single ME.
  • A MEG for a P2MP unidirectional path contains MEs destined for leaf nodes.
  • Section layer:

    Each ME forms a MEG.

  • LSP layer:

    Each ME forms a MEG.

  • PW layer:

    Each ME forms a MEG.

NOTE:

If two tunnels in opposite directions between LSR A and LSR D are established, a single MEG consisting of two MEs is established.

MEG end point (MEP)

A MEP is the source or sink node in a MEG.
  • Section layer: Each LSR can function as a MEP.

    Each LSR functions as an LSR.

  • LSP layer: Only an LER can function as a MEP.

    LSRs A, D, E, and G are LERs functioning as MEPs.

  • PW layer: Only PW terminating provider edge (T-PE) LSRs can function as MEPs.

    LSRs A and G are T-PEs functioning as MEPs.

MEG intermediate point (MIP)

Intermediate nodes between two MEPs on both ends of a MEG. MIPs only respond to OAM packets sent by MEPs and do not take the initiative in OAM packet exchanges.
  • Section layer:

    No MIPs.

  • LSP layer:

    LSRs B, C, and F function as MIPs.

  • PW layer:

    LSRs D and E function as MIPs.

Usage Scenario

MPLS-TP OAM monitors the following types of links:
  • Static bidirectional co-routed CR-LSPs
  • Static VLL-PWs and VPLS-PWs
Parent Topic: Understanding MPLS-TP OAM
Copyright © Huawei Technologies Co., Ltd.
Copyright © Huawei Technologies Co., Ltd.
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