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

Copyright © 2012, Juniper Networks, Inc.
1DM Transmission
When you start a one-way frame delay measurement, the router sends 1DM
frames—frames that carry the protocol data unit (PDU) for a one-way delay
measurement—from the initiator MEP to the receiver MEP at the rate and for the number
of frames you specify. The router marks each 1DM frame as drop-ineligible and inserts a
timestamp of the transmission time into the frame.
1DM Reception
When an MEP receives a 1DM frame, the router that contains the receiver MEP measures
the one-way delay for that frame (the difference between the time the frame was received
and the timestamp contained in the frame itself) and the delay variation (the difference
between the current and previous delay values).
One-Way ETH-DM Statistics
The router that contains the receiver MEP stores each set of one-way delay statistics in
the ETH-DM database. The ETH-DM database collects up to 100 sets of statistics for
any given CFM session (pair of peer MEPs). You can access these statistics at any time
by displaying the ETH-DM database contents.
One-Way ETH-DM Frame Counts
Each router counts the number of one-way ETH-DM frames sent and received:
• For an initiator MEP, the router counts the number of 1DM frames sent.
• For a receiver MEP, the router counts the number of valid 1DM frames received and the
number of invalid 1DM frames received.
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.
Synchronization of System Clocks
The accuracy of one-way delay calculations depends on close synchronization of the
system clocks at the initiator MEP and receiver MEP.
The accuracy of one-way delay variation is not dependent on system clock
synchronization. Because delay variation is simply the difference between consecutive
one-way delay values, the out-of-phase period is eliminated from the frame jitter values.
NOTE: For a given one-way Ethernet frame delay measurement, frame delay
and frame delay variation values are available only on the router that contains
the receiver MEP.
Chapter 14: Configuring ITU-T Y.1731 Ethernet Service OAM
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