ITU-T Y.1731 Performance
Monitoring in a Service Provider Network
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.
Prerequisites for ITU-T Y.1731 Performance Monitoring in a Service Provider Network
IEEE-compliant connectivity fault management (CFM) must be configured and enabled for Y.1731 performance monitoring to function.
Y1731 is supported over Port Channel interfaces.
ITU-T Y.1731 Performance Monitoring in a Service Provider Network
measurement message (DMM) with CFM over cross-connect on the router works only
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 rewritecommand 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.
LMM is not supported on the RSP3 module.
In ITU-T Y1731,
1DM measurement should mandate only PTP to have clock sync between sender &
Information About ITU-T Y.1731 Performance Monitoring in a Service Provider Network
Frame Delay and Frame-Delay
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:
level at which the MEP exists
Drop eligibility—marked drop ineligible
Total interval of
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
frame delay =
RxTimef – TxTimeStampf.
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)
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
stamp of the time at which the frame with ETH-DM request information was
stamp of the time at which the transmitting frame with ETH-DM reply information
The timestamping happens at the hardware level for DMM operations.
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.
Benefits of ITU-T 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.
How to Configure ITU-T Y.1731 Performance Monitoring in a Service Provider Network
The following new
commands were introduced that can be used to configure and display performance
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
Cisco IOS Debug
Configuration Examples for Configuring ITU-T Y.1731 Performance Monitoring Functions