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.
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