MICROCHIP AN1286 Ethernet Ring Protection Switch Configuration User Guide

MICROCHIP AN1286 Ethernet Ring Protection Switch Configuration User Guide

Introduction

This document explains how to setup Ethernet Ring Protection Switching (ERPS) features. Ethernet Ring Protection Switching is defined by the ITU G.8032 standard.
This implementation conforms to ITUT-G.8032(V1) and ITUT-G.8032(V2).

The ITU G.8032 standard defines the automatic protection switching (APS) protocol and protection switching mechanisms for Ethernet layer network (ETH) ring topologies. The protection protocol defined in ITU G.8032 enables protected pointto point, point-to-multipoint and multipoint-to-multipoint connectivity within a ring or interconnected rings, called “multi-ring/ladder network” topology. The ETH ring maps to the physical layer ring structure.

Each Ethernet ring node is connected to adjacent Ethernet ring nodes participating in the same Ethernet ring, using two independent links. A ring link is bounded by two adjacent Ethernet ring nodes and a port for a ring link is called a ring port. The minimum number of Ethernet ring nodes in an Ethernet ring is two.

Loop avoidance in an Ethernet ring is achieved by guaranteeing that, at any time, traffic may flow on all but one of the ring links. This particular link is called the ring protection link (RPL) and under normal conditions this ring link is blocked, i.e., not used for service traffic. One designated Ethernet ring node, the RPL owner node, is responsible for blocking traffic at one end of the RPL. Under an Ethernet ring failure condition, the RPL owner node is responsible for unblocking its end of the RPL, unless the RPL has failed, allowing the RPL to be used for traffic. The other Ethernet ring node adjacent to the RPL, the RPL neighbour node, may also participate in blocking or unblocking its end of the RPL.

The following conditions of the Ethernet ring are supported:

• Signal fail (SF) – When an SF condition is detected on a ring link and it is determined to be a “stable” failure, Ethernet ring nodes adjacent to the failed ring link initiate the protection switching mechanism.

• No request (NR) – The condition when no local protection switching requests are active. The following administrative commands are supported:

• Forced switch (FS) – This command forces a block on the ring port where the command is issued.

• Manual switch (MS) – In the absence of a failure or FS, this command forces a block on the ring port where the command is issued.

• Clear – The Clear command, at the Ethernet ring node, is used for the following operations.

  • Clearing an active local administrative command (e.g., FS or MS).
  • Triggering reversion before the wait to restore (WTR) or wait to block (WTB) timer expires in the case of revertive operation.
  • Triggering reversion in the case of non-revertive operation.
    Revertive and non-revertive switching.

• In revertive operation, after the condition(s) causing a switch has/have cleared, the traffic channel is restored to the working transport entity, i.e., blocked on the RPL.
  If a defect is cleared, the traffic channel reverts after the expiry of a WTR timer, which is used to avoid toggling protection states in the case of intermittent defects.

• In non-revertive operation, the traffic channel continues to use the RPL, if it has not failed, after a switch condition has cleared.

Protection switching shall be performed when:

• SF is declared on one of the ring links and the detected SF condition has a higher priority than any other local request or far-end request
• the received R-APS message requests to switch and it has a higher priority than any other local request
• initiated by operator control (e.g., FS, MS) if it has a higher priority than any other local request or far-end request.

ERPS Protocols

ERPS information is carried within the R-APS PDU which is one of a suite of Ethernet OAM PDUs. OAM PDU formats for each type of Ethernet OAM operation are defined in ITU-T Rec. Y.1731.

Configuration

In the normal case, an ERPS configuration requires CFM MEP instances to be instantiated in both ends of a protected flow. However, if the ring nodes are connected back-to-back, that is, without going through another network of switches, you may rely on the physical link directly without using a CFM MEP for signal fail. In that case use “sf-trigger link”.

An example of an ERPS configuration is shown below, with the associated CFM configuration:

Configuration of parameters

The syntax for ERPS global level CLI configuration command is:

Where:

The syntax for ERPS level CLI configuration command is:

Where:

An example is shown below:

Using control commands

The syntax for ERPS level CLI command is:

Where:

Example:

Show status and statistics

The syntax of the show erps CLI command is:

Where:

Example show statistics:

Example show status:

Configure three switch ring example

A simple three switch network is constructed to demonstrate how the ERPS features can be configured. The network is shown below.

The following commands will disable STP and LLDP, enable C-Port on Port 1 and 2 on all 3 switches.

The 3 individual switches are now configured like this:
Configure CFM and ERPS on Switch 1

Configure CFM and ERPS on Switch 2

Configure CFM and ERPS on Switch 3

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