Ethernet OAM Overview
Configuring Ethernet OAM
page 35-6
OmniSwitch AOS Release 7 Network Configuration Guide
June 2013
One-way ETH-DM
•
A MEP sends one-way delay measurement (1DM)) frames to a peer MEP. The sending MEP inserts
the transmission time into the 1DM frame at the time the frame is sent.
•
When a MEP receives a 1DM frame, the MEP calculates the one-way delay as the difference between
the time at which the frame was received and the transmission time indicated by the frame timestamp
(receive time minus transmission time).
•
One-way delay measurement statistics are gathered and stored on the receiving MEP (the MEP that
receives a 1DM request).
•
One-way ETH-DM requires clock synchronization between the sending and receiving MEPs. Using
NTP for clock synchronization is recommended.
Two-way ETH-DM
•
A MEP sends delay measurement message (DMM) frames to a peer MEP to request a two-way ETH-
DM. The sending MEP inserts the transmission time into the DMM frame at the time the frame is sent.
•
When a MEP receives a DMM frame, the MEP responds to the DMM with a delay message reply
(DMR) frame that contains the following timestamps:
– Timestamp copied from the DMM frame.
– Timestamp indicating when the DMM frame was received.
– Timestamp indicating the time at which the receiving MEP transmitted the DMR frame back to the
sending MEP.
•
When a MEP receives a DMR frame, the MEP compares all the DMR timestamps with the time at
which the MEP received the DMR frame to calculate the two-way delay.
•
The two-way delay is the difference between the time the originating MEP sent a DMM request and the
time at which the originating MEP received a DMR frame minus the time taken by the responding
MEP to process the DMM request.
•
Two-way delay measurement statistics are gathered and stored on the originating MEP (the MEP that
initiates a DMM request).
•
This method
does not
require clock synchronization between the transmitting and receiving MEPs.
•
Two-way ETH-DM is an on-demand OAM performance measurement. To set up continuous two-way
delay measurement, see
Chapter 36, “Configuring Service Assurance Agent,”
for information about
how to configure a SAA for continuous two-way frame delay measurement.
Frame Delay Variation
The delay variation (jitter) for both one-way and two-way ETH-DM is determined by calculating the
difference between the current delay measurement value and the previous delay measurement value. If a
previous delay value is not available, which is the case when a DM request is first made, then jitter is not
calculated.