Understanding Y.1731 Performance Monitoring
When service providers sell connectivity services to a subscriber, a Service Level Agreement (SLA) is reached between the buyer and seller of the service. The SLA defines the attributes offered by a provider and serves as a legal obligation on the service provider. As the level of performance required by subscribers increases, service providers need to monitor the performance parameters being offered. To capture the needs of the service providers, organizations have defined various standards such as IEEE 802.1ag and ITU-T Y.1731 that define the methods and frame formats used to measure performance parameters.
Y.1731 Performance Monitoring (PM) provides a standard ethernet PM function that includes measurement of ethernet frame delay, frame delay variation, frame loss, and frame throughput measurements specified by the ITU-T Y-1731 standard and interpreted by the Metro Ethernet Forum (MEF) standards group. As per recommendations, the ME 3400E switches should be able to send, receive and process PM frames in intervals of 1000ms (1000 frames per second) with the maximum recommended transmission period being 1000ms (1000 frames per second) for any given service.
To measure SLA parameters such as frame delay or frame delay variation, a small number of synthetic frames are transmitted along with the service to the end point of the maintenance region, where the Maintenance End Point (MEP) responds to the synthetic frame. For a function such as connectivity fault management, the messages are sent less frequently, while performance monitoring frames are sent more frequently.
Figure 1-1 illustrates Maintenance Entities (ME) and Maintenance End Points (MEP) typically involved in a point-to-point metro ethernet deployment for the Y.1731 standard.
Figure 1-1 A Point-to-Point Metro Ethernet Deployment with Typical Maintenance Entities and Maintenance Points
Performance monitoring parameters include
- Connectivity, page 41-2
- Frame Delay and Frame Delay Variation, page 41-2
- Frame Loss Ratio and Availability
Connectivity
The first step to performance monitoring is verifying the connectivity. Continuity check messages (CCM) are best suited for connectivity verification. Since they are optimized for fault recovery operation, they are not usually accepted as a component of an SLA due to the timescale difference between SLA and fault recovery. Instead, Connectivity Fault Management (CFM) and Continuity Check Database (CCDB) are used to verify connectivity. For more information on CFM see, Configuring Ethernet OAM, CFM, and E-LMI.
Frame Delay and Frame Delay Variation
Ethernet frame delay measurement (ETH-DM) is used for on-demand ethernet Operations, Administration, and Maintenance (OAM) to measure frame delay and frame delay variation.
Ethernet frame delay and frame delay variation are measured by sending periodic frames with ETH-DM information to the peer MEP and receiving frames with ETH-DM information from the peer MEP. During the interval, each MEP measures the frame delay and frame delay variation.
ETH-DM also collects information, such as worst and best case delays, average delay, and average delay variation. It provides a runtime display of delay statistics during a two-way delay measurement. ETH-DM records the last 100 samples collected per remote Maintenance End Point (MEP) or per CFM session.
These are the two methods of delay measurement, as defined by the ITU-T Y.1731 standard: One-way ETH-DM and Two-way ETH-DM. However, only Two-way ETH-DM is supported.
Two-way ETH-DM:
Each MEP transmits frames with ETH-DM request information to its peer MEP and receives frames with ETH-DM reply information from its peer MEP. Two way frame delay and frame delay variation are measured using delay measurement message (DMM) and delay measurement reply (DMR) frames.
Synthetic Loss Measurement
Synthetic Loss Measurement (ETH-SLM) is a mechanism to measure frame loss using synthetic frames, rather than data traffic. A number of synthetic frames are sent and received, and the number that are lost is calculated between a pair of MEPs. This number is used as a statistical sample to approximate the frame loss ratio of data traffic.
ETH-SLM transmits synthetic frames with ETH-SLM information to a peer MEP and similarly receives synthetic frames with ETH-SLM information from the peer MEP. Each MEP performs frame loss measurements which contribute to unavailable time.
A near-end frame loss refers to frame loss associated with ingress data frames. Far-end frame loss refers to frame loss associated with egress data frames. Both near-end and far-end frame loss measurements contribute to near-end severely errored seconds and far end severely errored seconds which together contribute to unavailable time.
ETH-SLM is measured using SLM and SLR frames. Although ITU-T Y.1731 defines two methods of frame loss measure, only Single-ended ETH-SLM is supported.
With Single-ended ETH-SLM, each MEP transmits frames with the ETH-SLM request information to its peer MEP and receives frames with ETH-SLM reply information from its peer MEP to complete synthetic loss measurements.
Supported Interfaces
Y.1731 PM supports these interfaces:
- SLM and DMM on Switchport on OFM
- SLM and DMM on Switchport on IFM
- SLM and DMM on PC Switchport OFM
- SLM and DMM on PC Switchport IFM
Restrictions and Usage Guidelines
Follow these restrictions and usage guidelines when you configure Y.1731 PM on the switch:
- Y.1731 PM is not supported on these interfaces:
– mLACP
– Port MEPs
– L2VFI
- Y.1731 PM is not supported on customer VLANs (C-VLANs). PM is only supported on service provider VLANs (S-VLANs).
- PM does not support SNMP, although CLI and system-logging is supported.
- Frame throughput measurements are not supported.
- Clock synchronization is not mandatory for Two-way delay measurement.
- For PM support on port-channels. adding or deleting a member link renders the session invalid.
- On-demand SLM/DMM is not supported on ME 3400E.
- SLM supports the following modes for sending frames:
– Continues Mode
– Burst Mode
- SLM supports frame interval of 1 sec and 100 ms.
Verifying Synthetic Loss Measurement Configurations
To verify the SLM configurations, use the following commands in privileged EXEC mode:
Switch# show ip sla statistics 2 details
IPSLAs Latest Operation Statistics
Loss Statistics for Y1731 Operation 2
Type of operation: Y1731 Loss Measurement
Latest operation start time: 14:47:36.954 IST Wed Nov 21 2012
Latest operation return code: OK
Start time: 14:47:36.954 IST Wed Nov 21 2012
Number of measurements initiated: 20
Number of measurements completed: 20
Unavailable indicators: 0
Min/Avg/Max - (FLR %): 0:9/000.00%/0:9
Cumulative - (FLR %): 000.00%
Min - 14:47:50.574 IST Wed Nov 21 2012
Max - 14:47:50.574 IST Wed Nov 21 2012
Unavailable indicators: 0
Min/Avg/Max - (FLR %): 0:9/000.00%/0:9
Cumulative - (FLR %): 000.00%
Min - 14:47:50.574 IST Wed Nov 21 2012
Max - 14:47:50.574 IST Wed Nov 21 2012
Switch# show ip sla history 100 interval-statistics
Loss Statistics for Y1731 Operation 100
Type of operation: Y1731 Loss Measurement
Latest operation start time: 10:36:28.610 UTC Mon May 14 2012
Latest operation return code: OK
Start time: 10:36:28.610 UTC Mon May 14 2012
End time: 10:37:28.610 UTC Mon May 14 2012
Number of measurements initiated: 594
Number of measurements completed: 594
Number of Observations 118
Available indicators: 118
Unavailable indicators: 0
Min/Avg/Max - (FLR %): 0:4/000.00%/0:4
Cumulative - (FLR %): 000.00%
Min - 10:37:28.246 UTC Mon May 14 2012
Max - 10:37:28.246 UTC Mon May 14 2012
Number of Observations 118
Available indicators: 118
Unavailable indicators: 0
Min/Avg/Max - (FLR %): 0:4/000.00%/0:4
Cumulative - (FLR %): 000.00%
Min - 10:37:28.246 UTC Mon May 14 2012
Max - 10:37:28.246 UTC Mon May 14 2012
To display the same outputs as the latest statistics detail command, use the show ip sla history interval n command. The number displayed is the number of intervals configured.
- Output for Loss Measurement:
Switch# show ip sla history 1 interval-statistics
Loss Statistics for Y1731 Operation 1
Type of operation: Y1731 Loss Measurement
Latest operation start time: *09:46:16.225 UTC Fri Nov 26 2010
Latest operation return code: OK
Start time: *09:46:16.225 UTC Fri Nov 26 2010
End time: *09:48:16.221 UTC Fri Nov 26 2010
Number of measurements initiated: 12006
Number of measurements completed: 12000
Number of Observations 11999
Max - *09:47:20.252 UTC Fri Nov 26 2010/ Min - *09:48:16.221 UTC Fri Nov 26 2010
Available indicators: 11999
Unavailable indicators: 0
Max/Avg/Min - (FLR %): 1:3/2.78%/0:0
Number of Observations 11999
Max - *09:48:16.221 UTC Fri Nov 26 2010/ Min - *09:48:16.221 UTC Fri Nov 26 2010
Available indicators: 11999
Unavailable indicators: 0
Max/Avg/Min - (FLR %): 0:0/0.0%/0:0
- Output for Delay Measurement:
Switch# show ip sla history 10 interval-statistics
Delay Statistics for Y1731 Operation 10
Type of operation: Y1731 Delay Measurement
Latest operation start time: 10:58:30.144 PDT Tue Jan 4 2011
Latest operation return code: Timeout
Start time: 10:58:30.144 PDT Tue Jan 4 2011
End time: 10:59:05.140 PDT Tue Jan 4 2011
Number of measurements initiated: 33
Number of measurements completed: 34
Number of TwoWay observations: 34
Max/Avg/Min TwoWay: 113364/100499/100099 (microsec)
Time of occurrence TwoWay:
Max - 10:59:05.140 PDT Tue Jan 4 2011
Min - 10:58:40.076 PDT Tue Jan 4 2011
Bin Range (microsec) Total observations
Number of TwoWay positive observations: 19
Max/Avg TwoWay positive: 13256/706 (microsec)
Time of occurrence TwoWay positive:
Max - 10:59:05.140 PDT Tue Jan 4 2011
Number of TwoWay negative observations: 14
Max/Avg TwoWay negative: 86/11 (microsec)
Time of occurrence TwoWay negative:
Max - 10:58:40.076 PDT Tue Jan 4 2011
Bin Range (microsec) Total observations
Bin Range (microsec) Total observations
To display the performance monitoring session summary, use the show ethernet cfm pm session summary command.
Switch# show ethernet cfm pm session summary
Number of Configured Session : 1
Number of Active Session: 1
Number of Inactive Session: 0
To display the SLM configurations, use the show run | b ip sla command in privileged EXEC mode.
Switch# show run | b ip sla
ethernet y1731 loss SLM domain PROVIDER_DOMAIN_VLAN evc domain_vlan101@101 mpid 101 cos 2
ethernet y1731 loss SLM burst domain PROVIDER_DOMAIN_VLAN evc domain_vlan101@101 mpid 101
availability algorithm static-window
ip sla schedule 103 start-time now
ip sla enable reaction-alerts
Switch# show ip sla configuration
IP SLAs Infrastructure Engine-III
Operation timeout (milliseconds): 0
Ethernet Y1731 Loss Operation
Domain: PROVIDER_DOMAIN_VLAN
Request size (Padding portion): 64
Operation frequency (seconds): 20 (not considered if randomly scheduled)
Next Scheduled Start Time: Pending trigger
Randomly Scheduled : FALSE
Entry Ageout (seconds): never
Recurring (Starting Everyday): FALSE
Status of entry (SNMP RowStatus): Active
Threshold (milliseconds): 0
Frame consecutive loss-ratio: 10
Availability algorithm: sliding-window
Operation timeout (milliseconds): 0
Ethernet Y1731 Loss Operation
Domain: PROVIDER_DOMAIN_VLAN
Request size (Padding portion): 64
Operation frequency (seconds): 20 (not considered if randomly scheduled)
Next Scheduled Start Time: Start Time already passed
Randomly Scheduled : FALSE
Entry Ageout (seconds): never
Recurring (Starting Everyday): FALSE
Status of entry (SNMP RowStatus): Active
Threshold (milliseconds): 0
Aggregate interval burst-cycles: 1
Frame consecutive loss-ratio: 10
Availability algorithm: static-window