Ethernet Frame Delay Measurements

On a Juniper Networks MX Series Ethernet Services Router equipped with the Distributed Port Concentrator (MX-DPC) only, you can perform Ethernet frame delay measurements (referred to as ETH-DM in Ethernet specifications). This feature allows you to configure on-demand Operation, Administration, and Maintenance (OAM) statements for the measurement of frame delay and frame delay variation (jitter). You can configure Ethernet frame delay measurement in either one-way or two-way (round-trip) mode to gather frame delay statistics and simultaneous statistics from multiple sessions. Ethernet frame delay measurement provides fine control to operators for triggering delay measurement on a given service and can be used to monitor Service Level Agreements (SLAs).

Ethernet frame delay measurement also collects other useful information, such as worst and best case delays, average delay, and average delay variation. Ethernet frame delay measurement supports hardware-based timestamping in the receive direction for delay measurements. It also provides runtime display of delay statistics when two-way delay measurement is triggered. Ethernet frame delay measurement records the last 100 samples collected per remote maintenance end point (MEP) or per connectivity fault management (CFM) session. You can retrieve the history at any time using simple commands. You can clear all Ethernet frame delay measurement statistics and PDU counters. Ethernet frame delay measurement is fully compliant with the ITU-T Y.1731 (OAM Functions and Mechanisms for Ethernet-based Networks) specification.

Ethernet frame delay measurement uses the IEEE 802.1ag CFM infrastructure.

An overview of the architecture established for Ethernet OAM is shown in Figure 1. Generally, Ethernet frame delay measurements are made in a peer fashion from one MEP or CFM session to another. However, these measurements are not made to Maintenance Intermediate Points (MIPs).

Figure 1: Ethernet OAM Overview

• One-way
• Two-way (round-trip)

For one-way Ethernet frame delay measurement, either MEP can send a request to begin a one-way delay measurement to its peer MEP. However, the statistics are collected only at the receiver MEP. This feature requires the clocks at the transmitting and receiving MEPs to be synchronized. If these clocks fall out of synchronization, only one-way delay variation and average delay variation values are computed correctly (and therefore valid). Use the show commands at the receiver MEP to display one-way delay statistics.

For two-way (round-trip) Ethernet frame delay measurement, either MEP can send a request to begin a two-way delay measurement to its peer MEP, which responds with timestamp information. Run-time statistics are collected and displayed at the initiator MEP. The clocks do not need to be synchronized at the transmitting and receiving MEPs. The Junos OS supports the optional timestamps in delay measurement reply (DMR) frames to increase the accuracy of delay calculations. The Junos OS also supports hardware-assisted timestamping for Ethernet frame delay protocol data units (PDUs) in the reception path.

Use the show commands at the initiator MEP to display two-way delay statistics, and at the receiver MEP to display one-way delay statistics.

• This feature is available only on MX Series routers.
• Ethernet frame delay measurements are available only when the distributed periodic packet management daemon (ppmd) is enabled.
• The statistics collected are lost after graceful Routing Engine switchover (GRES).
• You can monitor only one session to the same remote MEP or MAC address.
• Accuracy is compromised when the system changes (such as from reconfiguration). We recommend performing Ethernet frame delay measurements on a stable system.
• The use of Ethernet frame delay measurements on aggregated Ethernet and pseudowire interfaces is not supported.
• The use of hardware-assisted timestamping is not supported on all MX DPCs (Rev-B or higher is required).
• If you attempt to perform Ethernet frame delay measurements to a non-MX partner, the incoming Ethernet frame delay PDUs are discarded silently. Ethernet delay measurement commands and capabilities are not available on non-MX routers.