Ethernet Service OAM (802.1ag/Y.1731)

Ethernet Service OAM standards provide a framework to continuously monitor key SLA performance metrics at layer 2. These standards are designed to provide a uniform set of tests and resulting measurements that can be implemented directly in network elements and NIDs, providing consistent, interoperable monitoring across multi-vendor networks.

The key features of Ethernet Service OAM are end-to-end service visibility, fault isolation, reporting, and continuous performance monitoring. As specified in the IEEE 802.1ag and Y.1731 standards, these capabilities enable service providers to manage Ethernet services regardless of the network path, topology, operator, or network layer that carries the traffic between service endpoints.

This article describes how to configure Ethernet Service OAM on the Accedian demarcation devices.

Overview

Ethernet Service OAM defines a set of protocols to provide Fault Management (FM) capabilities as well as the ability to perform Performance Monitoring (PM) for Ethernet services.

IEEE 802.1ag, ITU-T Y.1731, and MEF OAM standards are based on a common multi-domain network model. The model reflects services delivered by multiple providers or operators at different levels. The domain hierarchy ensures OAM is contained within pre-defined maintenance levels.

Service OAM Fault Management Functionalities

Ethernet Service OAM includes the following Fault Management (FM) functionalities:

Connectivity Check Messages (CCM)
Connectivity check messages are “Heart beat” messages for CFM. The CCM provides a means to detect connectivity failures in a MEG. CCMs are multicast messages and are confined to a domain (MD). These messages are unidirectional and do not solicit a response. Each MEP transmits a periodic multicast CCM inward towards the other MEPs.
The MEP Statistics window provides a means to verify CCM statistics for messages sent and received, and Remote Defect Indicator (RDI) message presence.

Loopback Messages (LBM)
Loopback messages, also known as “MAC ping” or “Layer-2 ping” are unicast frames that a MEP transmits. They are similar in concept to the IP “Ping” command. Sending Loopback to successive MIPs can determine the location of a fault. A MEP can send an LBM to any MEP or MIP in the service. Unlike CCMs, LBMs do not run on their own; they need to be initiated and stopped by an administrator or operator.

Link Trace Messages (LTM)
Link trace messages are multicast frames that a MEP transmits to track the path (hop-by-hop) to a destination MEP. This process is also known as “MAC Trace Route,” and is similar in concept to the User Datagram Protocol (UDP) Trace Route. When an LTM is sent to an End Point (MEP), all intermediate points (MIP) respond with an LTR along the path travelled by the LTM. The returned LTRs (and those not returned) identify the segment or point where the fault originates.

Service OAM Performance Monitoring Functionalities

In addition to Fault Management, Ethernet Service OAM also supports various Performance Monitoring (PM) functionalities:

Frame Delay and Delay Variation (DMM)
Y.1731 specifies techniques for both one-way and round-trip frame delay and frame delay variation. One-way delay and delay variation measurements require that the service endpoints have synchronized reference clocks, while round-trip delay measurements do not.

Frame Loss (PL)
CCM messages are used to determine bi-directional frame loss ratios for a service. Counters at the service endpoints measure the number of sent, received and dropped packets.

Synthetic Loss Measurements (SLM)
Synthetic Loss Measurement (SLM) is used to measure the frame loss ratios (near-end and far-end) between two MEPs. Measurements and calculations are performed at one end only, the other being used as a reflector. The SLM instance is configured on the unit where you want to display the SLM measurements.

Vendor-Specific Protocol (VSP)
ETH-VSP is used for vendor-specific OAM functionality, which may be used by a vendor across its equipment. Accedian Networks uses VSP to perform frame loss and delay measurements between its V-NID products and the MetroNID and MetroNODE products. The V-NID is used as a VSP generator, while the MetroNID/MetroNODE units are reflectors.

Configuration Examples

• Example 1: Configuring Connectivity Fault Management (CFM)
• Example 2: Configuring an Up MEP
• Example 3: Configuring a MEG Intermediate Point (MIP)
• Example 4: Fault Validation and Isolation using LBM and LTM
• Example 5: Configuring Delay Measurements (DMM)
• Example 6: Configuring Frame Loss measurements with PL
• Example 7: Configuring Frame Loss measurements with SLM
• Example 8: Configuring SOAM for dual-tagged frames
• Example 9: Configuring VSP for inter-operation with V-NID

In order to illustrate the various options than can be used with Ethernet Service OAM, the following setup is used in all the configuration examples presented in this article.

Traffic Attributes:

• The subscriber’s service frames are tagged with C-VLAN 100.
• The Service Provider adds a tag (S-VLAN 2000) in its domain (done in NID2 and NID4).

Example 1: Configuring Connectivity Fault Management (CFM)

Connectivity Fault Management (CFM) is the most basic function of Ethernet Service OAM. It is also a pre-requisite to configure the Performance Monitoring functions (PL, SLM and DMM).

Configuration Procedure:

• Configure the MD Levels
• Configure the MEGs
• Configure the MEPs
• Validate the MEP status
• View the MEP results

Configure the MD Levels
Eight Maintenance Domain (MD) levels are available to accommodate different network deployment scenarios. MD levels define how far Service OAM frames will go, or which domains they are allowed to traverse.

Because Y.1731 does not use MD level names, the system has eight pre-defined pseudo-names for the Maintenance Domains (MD), one for each level, named Y.1731 level 0 to Y.1731 level 7.

These MD names exist only to simplify the integration of MEGs for Y.1731 with the CFM (802.1ag) MIB, which requires MD names. Users can create custom MD names if they choose to operate in 802.1ag mode. In this example, however, you will operate in Y.1731 mode and use the default MD level names.

Based on the maintenance domain structure shown in Figure 1, you will define MEG1 (Level 4) in the Provider’s Domain and MEG2 (Level 5) in the Subscriber’s Domain:

Configure the MEGs

1. Connect to NID2.

2. Access the page SOAM ▶ CFM ▶ MA/MEG and click Add.

3. Create a MEG instance (MEG1) at Level 4 by entering all parameters, as shown in the figure below, and click Apply.

4. Connect to NID4 and repeat the last two steps to create the same MEG instance.

5. Connect to NID1.

6. Access the page SOAM ▶ CDF ▶ MA/MEG and then click Add.

7. Create a MEG instance (MEG2) at Level 5 by entering all parameters, as shown in the figure below, and click Apply.
   

8. Connect to NID5 and repeat the last two steps to create the same MEG instance.

Configure the MEPs

1. Connect to NID2.

2. Access the page SOAM ▶ CFM ▶ MEP and click Add.

3. Create a MEP instance by entering all parameters, as shown in the figure below, and click Apply.

4. Connect to NID4 and repeat the last two steps to create the other MEP instance. Note that the MEPID is 2.

5. Connect to NID1.

6. Access the page SOAM ▶ CFM ▶ MEP and click Add.

7. Create a MEP instance by entering all parameters, as shown in the figure below, and click Apply.

8. Connect to NID5 and repeat the last two steps to create the other MEP instance. Note that the MEPID is 2.

Validate the MEP status

1. Connect to any of the units where you configured MEPS (e.g. NID1)
2. Access the page SOAM ▶ CFM ▶ MEP ▶ Status. If everything has been configured correctly, the status should be as follows:

All fault indicators should be at “I” (Inactive). “A” would identify an Active fault.

3. Access the page SOAM ▶ CFM ▶ MEP ▶ Statistics. This page shows a high-level summary of the CCM frames that have been sent between the MEPs, as well as those which carry a Remote Defect Indicator (RDI). Click the Broom icon in the top-right corner to clear the statistics. If everything has been configured correctly, the statistics should be as follows:

4. Click “1” under MEPID to see a detailed count for all types SOAM frames received and sent on the MEP.

Example 2: Configuring an Up MEP

Each MEP has a direction; down or up. A Down MEP receives CFM PDUs from the LAN and sends CFM PDUs towards the LAN. An Up MEP receives CFM PDUs from a bridge relay entity and sends CFM PDUs towards the bridge relay entity on a bridge.

In Example 1, you configured down MEPs on MEG1 and MEG2. You will now create a third MEG (MEG3, Level 6) on NID1 and NID5, and configure Up MEPs.

Configuration Procedure:
Configure the MEG.
Configure the Up MEPs.
Validate the configuration.

Configure the MEG

1. Connect to NID1.

2. Access the page SOAM ▶ CFM ▶ MA/MEG and click Add.

3. Create a MEG instance (MEG3) at Level 6 by entering all parameters, as shown in the figure below, and click Apply.

4. Connect to NID5 and repeat the last two steps to create the same MEG instance.

Configure the Up MEPs

1. Connect to NID1.

2. Access the page SOAM ▶ CFM ▶ MEP and click Add.

3. Create a MEP instance by entering all parameters, as shown in the figure below, and click Apply. Take note that this MEP will be on the Client port, its Direction will be set to Up, and it will be assigned MEPID 1.

4. Connect to NID4 and repeat the last two steps to create the other MEP instance. Note that the MEPID is 2.

Validate the configuration

1. Connect to NID1 or NID 5.

2. Access the page SOAM ▶ CFM ▶ Stack. If everything has been configured correctly, the new Up MEP on port Client should be visible in the CFM stack:

Example 3: Configuring a MEG Intermediate Point (MIP)

A MIP is a provisioned OAM reference point capable of reacting to diagnostic OAM frames initiated by MEPs, such as LBM and LTM frames. A MIP does not initiate proactive or diagnostic OAM frames. MIPs are used for Fault Management.

In Example 1, you configured down two Down MEPs on MEG1 (Level 4), in NID2 and NID4. You will now create MIPs on the same level in NID3.

Configuration Procedure:
Configure the MEG.
Create MIP via CFM default configuration.
Validate the configuration.

Configure the MEG

1. Connect to NID3.

2. Access the page SOAM ▶ CFM ▶ MA/MEG and click Add.

3. Create a MEG instance (MEG1) at Level 4 by entering all parameters, as shown in the figure below, and click Apply.

Note that MHF creation is set to Default, which instructs the system to use the CFM Defaults to control the creation of MIP Half Functions (MHF).

Create MIP via the CFM Default configuration

1. Access the page SOAM ▶ CFM ▶ Defaults and configure as follows:

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This creates a MIP on the Client and Network ports.

Validate the configuration

1. Connect to NID1 or NID 5.

2. Access the page SOAM ▶ CFM ▶ Stack:

Note that a MIP is composed of two MIP half Functions (MHF); Up and Down. Therefore, this screen capture shows two MIPs (with a total of four Half Functions); one MIP on the Client port and one on the Network port.

Example 4: Fault Validation and Isolation using LBM and LTM

This example shows how to use the LBM and LTM functionalities to validate or isolate faults.

Example 4, Part 1: Loopback Message (LBM):

Configuration Procedure:

• Configure a MEG and two MEPs as in Example 1
• Configure LBM

Configure a MEG and two MEPs as in Example 1

1. Refer to Example 1 on .

Configure LBM

1. Connect to a unit.

2. Access the page SOAM ▶ CFM ▶MEP ▶ LBM. This page displays an LBM instance for each MEP that is configured in the system:

3. Click a MEPID. E.g., Index 2, MEPID 1:

The function is configured by default to send LBMs to its remote MEP, based on the MEPID (Target type). However, you can also change the Target type to send unicast LBMs to a specific MAC address, or to send multicast LBMs if needed.

4. Set the number of messages (LBM) to send and click Apply.

The LBM test results are displayed at the bottom of the screen.
To send an LBM to a MIP, set Target type to MAC address and enter the MAC of the MIP in the MAC address field.
Example 4, Part 2: Link Trace Message (LTM):
Configuration Procedure:

• Configure a MEG and two MEPs as in Example 1.
• Configure LBM.

Configure a MEG and two MEPs as in Example 1

1. Refer to Example 1

Configure LTM

1. Connect to a unit.

2. Access the page SOAM ▶ CFM ▶MEP ▶ LTM. This page displays an LBM instance for each MEP that is configured in the system:
   

3. Click a MEPID. E.g., Index 1, MEPID 1:
   

4. Click Start to initiate a Link Trace:

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The Link Trace results are displayed at the bottom of the screen.

Going back to Example 3 (Configuring a MIP), if you run a Link Trace from NID2 to NID4, you should expect the MIP in NID3 to reply to the LTM.

The Link Trace results should be similar to the following:

Example 5: Configuring Delay Measurements (DMM)

This example shows how to configure Delay Measurements (DMM) between end points.

Y.1731 delay measurements are based on a four-timestamp method. This method is used to eliminate any processing time used by the far-end unit to loop the OAM frames back, so that you get a true measurement of the network delay and delay variation.
DMM/DMR Flow:

• When configured for two-way delay measurements, a MEP periodically transmits DMM frames with the TxTimeStampf value (timestamp at the time the DMM frame is transmitted).
• When the remote MEP receives a DMM frame, it replies with a DMR frame. The remote MEP adds the RxTimeStampf value (timestamp at the time of receiving the DMM frame) and the TxTimeStampb value (timestamp at the time of transmitting the DMR frame).
• Upon receiving a DMR frame, a MEP registers RxTimeb (reception time of the DMR frame).

• The frame delay for one-way and two-way is then calculated as follows:
  Frame Delaytwo-way = (RxTimeb - TxTimeStampf) - (TxTimeStampb - RxTimeStampf)
  Frame Delayone-way_near-end = RxTimeb - TxTimeStampb

Configuration Procedure:

• Configure a MEG and two MEPs as in Example 1 on page 5.
• Configure DMM on both end points.
• View the results.

Configure a MEG and two MEPs as in Example 1

1. Refer to Example 1

Configure DMM on both end points

1. Connect to NID2.

2. Access the page SOAM ▶ CFM ▶ DMM ▶ Configuration and click Add.

3. Create a DMM instance as shown in the figure below, and click Apply.

4. Connect to NID4 and repeat the last two steps to create a DMM instance on the remote end point.

View the results

1. In NID2, access the page SOAM ▶ CFM ▶ DMM ▶ Results and click index 1.

Example 6: Configuring Frame Loss Measurements with PL

This example describes how to configure the Packet Loss (PL) functionality. PL uses the Continuity Check Message (CCM) frames that are sent between MEPs to measure frame loss. Frame loss is always measured from the far-end MEP to the near-end MEP. If frame loss needs to be monitored from the local MEP to the remote MEP, a PL instance must be configured on the remote MEP as well.

Configuration Procedure:

• Configure a MEG and two MEPs as in Example 1 on page 5.
• Configure PL on both end points.
• View the results.

Configure a MEG and two MEPs as in Example 1

1. Refer to Example 1 on page 5.

Configure PL on both end points

1. Connect to NID2.

2. Access the page SOAM ▶ CFM ▶ Packet Loss ▶ Configuration and click Add.

3. Create a PL instance as shown in the figure below, and click Apply.

4. Connect to NID4 and repeat the last two steps to create a PL instance on the remote MEP.

View the results

1. In NID2, access the page SOAM ▶ CFM ▶ Packet Loss ▶ Results and click index 1.

Click Refresh if needed to reload the results or use the Poll checkbox to do it automatically.

The bottom section displays the results on a continuous basis. Click Clear to reset the statistics.

Example 7: Configuring Frame Loss Measurements with SLM

This example describes how to configure the Synthetic Loss Measurement (SLM) functionality. SLM needs to be configured on one end point only. The other end point (remote MEP) acts as a reflector. It also sends its results to the local MEP where they can be viewed.

Configuration Procedure:

• Configure a MEG and two MEPs as in Example 1 on page 5.
• Configure SLM on one MEP.
• View the results.

Configure a MEG and two MEPs as in Example 1

1. Refer to Example 1.

Configure SLM on one MEP

1. Connect to NID2.

2. Access the page SOAM ▶ CFM ▶ SLM ▶ Configuration and click Add.

3. Create an SLM instance as shown in the figure below, and click Apply.

View the results

1. In NID2, access the page SOAM ▶ CFM ▶ SLM ▶ Results and click index 1.

Click Refresh, if needed, to reload the results or use the Poll checkbox to do it automatically.

The bottom section displays the results on a continuous basis. Click Clear to reset the statistics.

Example 8: Configuring SOAM for dual-tagged frames

As of firmware version 6.2, most Accedian demarcation devices (except the EtherNID and MetroNID TE platforms) support Service OAM dual-tagged frames (stacked VLANs). Once a MEG is set up for dual-VLAN tagging, all SOAM instances (MEP, DMM, PL, and SLM) that are created afterwards will automatically inherit the dual-tag configuration.

This example describes how to configure the unit to send dual-tagged SOAM frames. The SOAM frames will be tagged as follows:

• Outer tag: S-VLAN 2000
• Inner tag: C-VLAN 100

Setup:

Configuration Procedure:

• Configure a VLAN interface for the outer tag.
• Assign the interface to the list of CFM interfaces.
• Create a MEG.
• Create a MEP.

Configure a VLAN interface for the outer tag

1. Connect to NID1.

2. Access the page System ▶ Configuration ▶ Interface and click Add.

3. Create a VLAN interface with the outer tag (S-VLAN 2000) on the port where the MEP will be configured (Port 4).

Assign the interface to the list of CFM interfaces

1. Access the page SOAM ▶ CFM ▶ Interface. Select the new interface (MEP_S2000) in the pull-down menu and click Assign.

Once assigned, the interface is displayed in the list and available for CFM:

Create a MEG

1. Access the page SOAM ▶ CFM ▶ MA/MEG and click Add.

2. Create a MEG instance (MEG1) at Level 4 by entering all parameters, as shown in the figure below, and click Apply.

Note that the VLAN is set to C-VLAN 100, which is the inner tag. The inner tag is defined in the MEG configuration. The outer tag, on the other hand, is defined in an interface, as you did in the first two parts of this procedure.

Create a MEP

1. Access the page SOAM ▶ CFM ▶ MEP and click Add.

2. Create a MEP instance by entering all parameters, as shown in the figure below, and click Apply.

Repeat this procedure in NID2 to configure the remote end point.

Example 9: Configuring VSP for inter-operation with V-NID

This example describes how to configure a MetroNID or MetroNODE unit as a VSP reflector to inter-operate with an Accedian V-NID. In this configuration, the V-NID is used as a VSP generator. The V-NID send VSP frames to the reflector unit (MetroNID or MetroNODE). The V-NID computes frames loss and one-way delay measurements (both directions).

Configure the MD Levels

1. Connect to a unit.

2. Access the page SOAM ▶ CFM ▶ VSP.

3. Select the MEG level for which VSP frames must be reflected; e.g., 4. Selecting All would reflect VSP frames for all MEG levels (0 - 7).

Abbreviations and Acronyms