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ITU-T Y.1731 performance monitoring provides standard-based Ethernet performance monitoring that encompasses the measurement of Ethernet frame delay, frame-delay variation, and throughput as outlined in the ITU-T Y.1731 specification and interpreted by the Metro Ethernet Forum (MEF). Service providers offer service level agreements (SLAs) that describe the level of performance customers can expect for services. This document describes the Ethernet performance management aspect of SLAs.
IEEE-compliant connectivity fault management (CFM) must be configured and enabled for Y.1731 performance monitoring to function.
 Note |
Y1731 is supported over Port Channel interfaces. |
The frame-delay measurement message (DMM) with CFM over cross-connect on the router works only if the control-word command is enabled.
When the core network has multiple paths, the Tx and Rx, DMM/DMR packets can be sent and received on different ports. If the ports belong to a different interface module (IM), time stamping can be out of sync and in certain cases the Rx value can be lower than the Tx value. This value is displayed as 0 in the raw database output. As a workaround, configure Precision Time Protocol (PTP) between the two connectivity fault management (CFM) endpoint routers.
RSP3 module supports ASIC-based timestamping. When the sending and receiving ports of the Tx and Rx packets are on the same ASIC module, there is no dys-synchronization between the sending and receiving ports. However, if the sending and receiving ports are on different ASIC modules, the Precision Time Protocol (PTP) is to be configured between the two connectivity fault management (CFM) endpoint routers.
Y.1731 is supported with the rewrite command configuration on Ethernet Flow Points (EFPs) throughout the Layer 2 circuit. However, the configuration may be in such a way that the Y1731 PDUs may be transmitted untagged. This results in the other end of the Layer 2 circuit not being able to ascertain the CoS value which determines the SLA session to which the PDUs belong. Therefore, the rewrite command configuration is not supported when CoS value is configured with IP SLA or the Y.1731 profile.
Y.1731 performance monitoring is not supported in MEPs that are configured on TEFP on the RSP3 module.
Y.1731 performance monitoring is not supported in MEPs that are configured on ports.
CFM and Y.1731 performance monitoring on a port-channel is not supported on the RSP3 mdoule, in Cisco IOS XE Release 3.18SP and earlier.
CFM and Y.1731performance monitoring on a port-channel is supported on the RSP3 module starting Cisco IOS XE Everest 16.5.1. The supported scale value is 500 sessions.
LMM is not supported on the RSP3 module.
Y.1731 DMM is not supported on the RSP3 platform, when there are two VLAN tags, two or more MPLS tag with control word enabled on the system.
Note |
In ITU-T Y1731, 1DM measurement should mandate only PTP to have clock sync between sender & receiver. |
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 value copied from the ETH-DM request information.
Two-way frame delay is calculated as (RxTimeb–TxTimeStampf)–(TxTimeStampb–RxTimeStampf), 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.
The timestamping happens at the hardware level for DMM operations.
Note |
The frame-loss, frame-delay, and frame-delay variation measurement processes are terminated when faults related to continuity and availability occur or when known network topology changes occur. |
An MIP is transparent to the frames with ETH-DM information; therefore, an 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.
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. For information about Y.1731 On-Demand and Concurrent Operations, see Configuring IP SLAs Metro-Ethernet 3.0 (ITU-T Y.1731) Operations.
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Feature Name |
Release Information |
Feature Description |
|---|---|---|
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Application of QoS Policies on ITU-T Y.1731 Egress Packets |
Cisco IOS XE Cupertino 17.9.1 |
You can now apply QoS policies on Y.1731 egress packets. Operations, Administration, and Maintenance (OAM) functions and mechanisms for Ethernet-based networks are defined in ITU-T Y.1731. With this implementation, you can prioritize OAM traffic; for example, prioritizing operational information used to detect faults and determining network performance. |
The number of Y.1731 egress packets that are dropped, due to bandwidth limitation, must be reflected accurately. To facilitate the application of QoS on Y.1731 egress packets, the following requirements are implemented:
Note |
We recommend that you maintain sufficient free QoS labels to enable QoS for Y.1731 egress packets. |
Y.1731 performance management probe packets are subject to QoS on the measurement nodes because they have appropriate packet type of service (ToS) marking to take the same path as regular data do through the transit nodes. Packets are processed identically in the transit path.
Y.1731 packet must bypass ingress QoS at user-network interface (UNI) and hit EQoS on the network-network interface (NNI) of endpoints.
Ensure that Y.1731 functionalities, such as delay measurement and frame-delay measurement message (DMM) packets, are considered as transit traffic, because these packets measure the delay of green packets in the network.
For MPLS, the CoS-EXP mapping is preserved for CPU-injected Y.1731 traffic.
In case of data traffic not marked with MPLS EXP at the imposition, all packets fall under the class-default policy-map at the egress. In such cases, if the Y.1731 sessions also have CoS 0 configured in them, then the Y.1731 packets are likely to get discarded, subject to the bandwidth availability.
It is supported only in L2VPN (Xconnect/VPLS) services.
It is not supported for EVC BD services.
It is not supported with CFM Down MEP sessions.
Follow the steps below to apply egress QoS on ITU-T Y.1731 egress packets:
Execute the platform qos-feature y1731-qos enable command to enable QoS for Y.1731 egress packets.
Note |
Use the no form of the command to disable QoS for Y.1731 egress packets. |
Execute the write memory command to save the running configuration as the startup configuration.
Reload the system for the configuration to take effect.
Router#show run | sec y1731-qos
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#platform qos-feature y1731-qos en
Router(config)#endRouter#show run | sec y1731-qos
platform qos-feature y1731-qos enable
Router#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#no platform qos-feature y1731-qos enable
Router(config)#endThis example shows the configuration of Y.1731 Dela Measurement Messages (DMM)/1DM frames and Synthetic Loss Measurement (SLM)/Loss Measurement Management (LMM):
ip sla 1
ethernet y1731 delay DMM domain d1 evc evc10 mpid 1002 cos 4 source mpid 1001
frame size 1000
frame interval 10
ip sla schedule 1 life forever start-time now
ip sla 2
ethernet y1731 delay 1DM domain d1 evc evc10 mpid 1002 cos 0 source mpid 1001
frame size 1000
frame interval 10
ip sla schedule 2 life forever start-time now
ip sla 3
ethernet y1731 loss SLM domain d1 evc evc10 mpid 1002 cos 6 source mpid 1001
frame size 1000
frame interval 10
ip sla schedule 3 life forever start-time now
ip sla 4
ethernet y1731 loss LMM domain d1 evc evc10 mpid 1002 cos 8 source mpid 1001
frame interval 10
ip sla schedule 4 life forever start-time now
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