Y.1731 synthetic loss measurement (ETH-SLM)

Y.1731 ETH-SLM (Synthetic loss measurement) is a mechanism for measuring frame loss using synthetic frames, rather than inspecting real customer data traffic.

ETH-SLM is used to perform on-demand or proactive tests by sending frames with ETH-SLM information to one or multiple peer MEPs and similarly receiving frames with ETH-SLM information from the peer MEPs. Each MEP then performs frame loss measurements based on the counters added to the frames. Since a bidirectional service is defined as unavailable if either of the two directions is declared unavailable, ETH-SLM must facilitate each MEP to perform near-end and far-end synthetic frame loss measurements.

Y.1731 ETH-SLM is a Layer 2 protocol, and Layer 2 connectivity is therefore required between the Test Agent and the device you are testing towards.


To run a Y.1731 measurement you need to have at least one Netrounds Test Agent installed as well as one or several Y.1731-enabled devices in your network. See the quick start guides in the Netrounds Test Agents section for guidance on how to deploy a new Test Agent. Regarding enabling of Y.1731 on your equipment, consult your equipment vendor.

You also need to prepare a Y.1731 MEP list in Netrounds, as explained on this page.

Then create a new test or monitoring and fill in the mandatory parameters below: 


Tests only

  • Duration (seconds): The duration of this test step in seconds. Min: 30 s. Max: 604800 s. Default: 60 s.
  • Fail threshold (seconds): The maximum number of errored seconds (ES) that may occur without triggering a fail for this test step. Default: 0.
  • Wait for ready: Time to wait before starting the test. The purpose of inserting a wait is to allow all Test Agents time to come online and acquire good time sync. Min: 1 min. Max: 24 hours. Default: "Don't wait", i.e. zero wait time.


  • Clients: Test Agents to act as initiating MEPs.
  • MEPs (MAC addresses): A list of reflector MEPs containing MAC addresses.  
  • Rate (Mbit/s): The rate at which the clients will send frames in Mbit/s.
  • Rate (packets/s): The rate at which the clients will send frames in packets/s. Min: 2 packets/s. Max: 1,000,000 packets/s.
  • Frame size (bytes): Layer 2 Ethernet frame size in bytes (definition). Min: 64 bytes. Max: 9018 bytes. Default: 1518 bytes.
  • Source MEP ID: The source MEP ID, which will be used by the Test Agent in the SLM request. Default: 0.

Once Frame size is defined, changing one Rate parameter will cause the other to adjust automatically to agree with it.

Thresholds for errored seconds (ES)

  • Loss (%): Packet loss threshold for triggering errored seconds. If the loss exceeds this value during one second, an ES will be indicated by Netrounds. Default: 0%.

Thresholds for severely errored seconds (SES)          

  • Loss (%): Packet loss threshold for triggering severely errored seconds. If the loss exceeds this value during one second, an SES will be indicated by Netrounds. No default.


  • VLAN priority (PCP): Specifies which Priority Code Point to use in the VLAN header. Default: 0.
  • Delayed start (s): (Tests only) Time by which to delay the start of the test within a test step. Default: 0 s.

SLA thresholds (monitorings only)

  • SLA Good: Threshold for good fulfillment of service level agreement. Default: 99.95%.
  • SLA Acceptable: Threshold for acceptable fulfillment of service level agreement. Default: 99.5%.

Result metrics

  • Rate (Mbit/s): Actual rate at which clients sent Y.1731 frames.
  • Sent (packets): Number of sent packets.
  • Received (packets): Number of received packets.
  • Lost near (packets): Number of lost packets, near end.
  • Loss near (%): Packet loss ratio, near end.
  • Lost far (packets): Number of lost packets, far end.
  • Loss far (%): Packet loss ratio, far end.
  • ES (%): Aggregated errored second (ES) percentage.
  • ES loss (%): Errored second percentage for packet loss.
  • SES (%): Aggregated severely errored second (SES) percentage.
  • Unavailable seconds (%): Unavailable seconds percentage.
  • SLA: Service level agreement fulfillment for the test or monitoring: equal to (100 – ES) %.
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