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ODU Path Delay Measurement for Performance Monitoring

 

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Understanding ODU Path Delay Measurement

Performance monitoring is an important requirement in any network, including the optical transport networks (OTN). The key parameters that impact performance are bit error rate (BER) and delay. Delays in data communication over a network impact the network latency. Network latency is the time taken for a packet of data to travel from a designated point to another designated point. If there are less delays, the network latency is low. You can measure latency by sending a packet and then receiving it as it is returned back to you; the time taken for the round-trip indicates the latency.

The optical channel data unit (ODU) path delay measurement offers in-service delay measurement. Delay (or latency) is measured by transmitting a known pattern (delay measurement pattern) in a selected bit of the delay measurement (DM) field and measuring the number of frames that are missed when the delay measurement pattern is received at the transmitting end. For instance, if the transmitted delay measurement bit is 1 1 1 1 1 1 1 1 1 0 0 and the received delay measurement bit is 1 1 1 0 0 0 0 0 0 0 0, the delay measurement starts at frame 2 and ends at frame 8. This can be detected by the change in value between the transmitted bit and the received bit.

The result of the delay measurement is 6 frames (8 - 2).

Guidelines for Configuring Delay Measurement

When you configure in-service delay measurement, we recommend that you follow certain guidelines to ensure that you obtain accurate delay measurement.

  • Unidirectional delay measurement is not supported. The in-service delay measurement is specific to round-trip delay measurement and for optical channel data units only.

  • Delay measurement on different framers for the MIC and PIC is different. So, the delay measurement values are different.

  • Resiliency is not supported for path delay measurement.

  • Links at the local and remote interfaces must be active before you configure delay measurement.

  • Do not perform delay measurement tests when ODU maintenance signals are injected.

  • Do not configure local loopback and network loopback with remote loopback because the loopback data is overwritten by the delay measurement pattern.

Note

If a link failure occurs after you begin measuring delay, delay measurement fails. You must re-enable measurement of delay on the local interface to measure delay.

Enabling ODU Path Delay Measurement

Delay measurement is disabled by default. This topic explains the broad steps for measuring the optical channel data units (ODU) path delay on optical transport networks (OTN). First, enable remote loopback on the remote interface and commit the configuration. This enables the remote interface to loop back the delay measurement pattern to the local interface. Then, start delay measurement at the local interface and view the results.

Note

Do not enable remote loopback on both ends (local and remote). If you enable remote loopback on both interfaces, the delay measurement pattern is looped back continuously between the two interfaces.

Before you start measuring delay in the ODU path on OTN, complete the following tasks:

  • Ensure that the links are active at the local and remote interfaces and alarms are not configured.

  • Ensure that there is a delay of 10 seconds before enabling remote loopback. Also, ensure that there is a delay of 10 seconds after enabling remote loopback at the remote interface and before you start measuring delay.

  • Ensure that the delay measurement tests are not performed when ODU maintenance signals are injected.

  • Ensure that the local loopback and network loopback are also not specified because the looped-back data is overwritten by the delay measurement pattern.

Note

If link failure occurs after you begin measuring delay, delay measurement fails. You must re-enable measurement of delay on the local interface to measure delay.

To enable ODU path delay measurement, first enable remote loopback of the delay measurement pattern on the remote interface and then start measurement of the delay.

  1. Enable remote loopback on the remote interface by including the remote-loop-enable statement at the [edit] hierarchy level.
  2. After enabling remote loopback, commit the configuration.
  3. Start delay measurement on the local interface by including the start-measurement statement at the [edit] hierarchy level.
  4. After enabling measurement of delay on the local interface, commit the configuration.
  5. To view the delay measurement values, from the operational mode, enter the show interfaces extensive command.

Disabling ODU Path Delay Measurement

Delay measurement is disabled by default. If you enabled optical channel data unit (ODU) path delay measurement by using the remote-loop-enable and start-measurement statements, you can use this procedure to disable delay measurement.

Note

You can also use the delete or deactivate command to disable remote loopback on the remote interface. For instance, you can use the delete interfaces interfacename otn-options odu-delay-management remote-loop-enable or deactivate interface interfacename otn-options odu-delay-management remote-loop-enable command to disable remote loopback on the remote interface.

To disable ODU path delay measurement, first disable remote loopback of the delay measurement pattern on the remote interface and then stop delay measurement:

  1. Stop delay measurement on the local interface by including the stop-measurement statement at the [edit] hierarchy level.
  2. After you stop delay measurement on the local interface, commit the configuration.
  3. Disable remote loopback on the remote interface by including the no-remote-loop-enable statement at the [edit] hierarchy level.
  4. After disabling remote loopback on the remote interface, commit the configuration.
  5. To verify that remote loopback is disabled and delay is not measured, enter the show interfaces extensive command, from the operational mode.