The Frame Delay parameter can be used for on-demand OAM measurements of frame delay and frame-delay variation. When a maintenance end point (MEP) is enabled to generate frames with frame-delay measurement (ETH-DM) information, it periodically sends frames with ETH-DM information to its peer MEP in the same maintenance entity. Peer MEPs perform frame-delay and frame-delay variation measurements through this periodic exchange during the diagnostic interval.

An MEP requires the following specific configuration information to support ETH-DM:

• MEG level—MEG level at which the MEP exists

• Priority

• Drop eligibility—marked drop ineligible

• Transmission rate

• Total interval of ETH-DM

• MEF10 frame-delay variation algorithm

A MEP transmits frames with ETH-DM information using the TxTimeStampf information element. TxTimeStampf is the time stamp for when the ETH-DM frame was sent. A receiving MEP can compare the TxTimeStampf value with the RxTimef value, which is the time the ETH-DM frame was received, and calculate one-way delay using the formula frame delay = RxTimef – TxTimeStampf.

One-way frame-delay measurement (1DM) requires that clocks at both the transmitting MEP and the receiving MEPs are synchronized. Measuring frame-delay variation does not require clock synchronization and the variation can be measured using 1DM or a frame-delay measurement message (DMM) and a frame-delay measurement reply (DMR) frame combination.

If it is not practical to have clocks synchronized, only two-way frame-delay measurements can be made. In this case, the MEP transmits a frame containing ETH-DM request information and the TxTimeStampf element, and the receiving MEP responds with a frame containing ETH-DM reply information and the TxTimeStampf valued copied from the ETH-DM request information.

Two-way frame delay is calculated as frame delay = RxTimeb – TxTimeStampf, where RxTimeb is the time that the frame with ETH-DM reply information was received. Two-way frame delay and variation can be measured using only DMM and DMR frames.

To allow more precise two-way frame-delay measurement, the MEP replying to a frame with ETH-DM request information can also include two additional time stamps in the ETH-DM reply information:

• RxTimeStampf—Time stamp of the time at which the frame with ETH-DM request information was received.

• TxTimeStampb—Time stamp of the time at which the transmitting frame with ETH-DM reply information was sent.

Note	Discard frame-delay and frame-delay variation measurements for continuity and availability faults or when known network topology changes occur.

An MIP is transparent to the frames with ETH-DM information; therefore, a MIP does not require information to support the ETH-DM function.

The figure below shows a functional overview of a typical network in which Y.1731 performance monitoring is used.

Figure 1. Y.1731 Performance Monitoring

Combined with IEEE-compliant connectivity fault management (CFM), Y.1731 performance monitoring provides a comprehensive fault management and performance monitoring solution for service providers. This comprehensive solution in turn lessens service providers’ operating expenses, improves their service-level agreements (SLAs), and simplifies their operations.

The following new commands were introduced that can be used to configure and display performance monitoring parameters: debug ethernet cfm pm, monitor loss counters, and show ethernet cfm pm.

For more information about CFM and Y.1731 performance monitoring commands, see the Cisco IOS Carrier Ethernet Command Reference. For more information about debug commands, see the Cisco IOS Debug Command Reference.

For Y.1731 performance monitoring configuration examples, see "Configuring IP SLAs Metro-Ethernet 3.0 ITU-T Y.1731 Operations" in the IP SLAs Configuration Guide.