Junos® OS Ethernet Interfaces Configuration ... - Juniper Networks

Two-Way ETH-DM Frame Counts
Each router counts the number of two-way ETH-DM frames sent and received:
• For an initiator MEP, the router counts the number DMM frames transmitted, the number
of valid DMR frames received, and the number of invalid DMR frames received.
• For a responder MEP, the router counts the number of DMR frames sent.
Each router stores ETH-DM frame counts in the CFM database. The CFM database stores
CFM session statistics and, for interfaces that support ETH-DM, any ETH-DM frame
counts. You can access the frame counts at any time by displaying CFM database
information for Ethernet interfaces assigned to MEPs or for MEPs in CFM sessions.
NOTE: For a given two-way Ethernet frame delay measurement, frame delay
and frame delay variation values are available only at the router that contains
the initiator MEP.
Choosing Between One-Way and Two-Way ETH-DM
One-way frame delay measurement requires that the system clocks at the initiator MEP
and receiver MEP are closely synchronized. Two-way frame delay measurement does
not require synchronization of the two systems. If it is not practical for the clocks to be
synchronized, two-way frame delay measurements are more accurate.
When two systems are physically close to each other, their one-way delay values are
very high compared to their two-way delay values. One-way delay measurement requires
that the timing for the two systems be synchronized at a very granular level, and MX
Series routers currently do not support this granular synchronization.
Restrictions for Ethernet Frame Delay Measurement
Copyright © 2012, Juniper Networks, Inc.
The following restrictions apply to the Ethernet frame delay measurement feature:
• The ETH-DM feature is not supported on aggregated Ethernet interfaces or
label-switched interface. (LSI) pseudowires.
• Hardware-assisted timestamping for ETH-DM frames in the reception path is only
supported for MEP interfaces on Enhanced DPCs and Enhanced Queuing DPCs in MX
Series routers. For information about hardware-assisted timestamping, see “Guidelines
for Configuring Routers to Support an ETH-DM Session” on page 253 and “Enabling the
Hardware-Assisted Timestamping Option” on page 263.
• Ethernet frame delay measurements can be triggered only when the distributed periodic
packet management daemon (ppm) is enabled. For more information about this
limitation, see “Guidelines for Configuring Routers to Support an ETH-DM Session” on
page 253 and “Ensuring That Distributed ppm Is Not Disabled” on page 261.
• You can monitor only one session at a time to the same remote MEP or MAC address.
For more information about starting an ETH-DM session, see “Starting an ETH-DM
Session” on page 264.
Chapter 14: Configuring ITU-T Y.1731 Ethernet Service OAM
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