7
How Ethernet
OAM works
This section describes the working procedures of Ethernet OAM.
Ethernet OAM connection establishment
Ethernet OAM connection is the base of all the other Ethernet OAM functions. OAM connection
establishment is also known as the “Discovery phase”, where an Ethernet OAM entity discovers remote
OAM entities and establishes sessions with them.
In this phase, interconnected OAM entities notify the peer of their OAM configuration information and
the OAM capabilities of the local nodes by exchanging Information OAMPDUs and determine whether
Ethernet OAM connections can be established. An Ethernet OAM connection can be established only
when the settings concerning loopback, link detecting, and link event of the both sides match. After an
Ethernet OAM connection is established, Ethernet OAM takes effect on both sides.
As for Ethernet OAM connection establishment, a device can operate in active Ethernet OAM mode or
passive Ethernet OAM mode.
Table 6
Active and passive Ethernet OAM modes
Item
Active Ethernet OAM mode
Passive Ethernet OAM mode
Initiating OAM Discovery
Available
Unavailable
Responding to OAM Discovery
Available
Available
Transmitting Information
OAMPDUs
Available Available
Transmitting Event Notification
OAMPDUs
Available Available
Transmitting Information
OAMPDUs without any TLV
Available Available
Transmitting Loopback Control
OAMPDUs
Available Unavailable
Responding to Loopback Control
OAMPDUs
Available—if both sides operate in
active OAM mode
Available
NOTE:
•
OAM connections can be initiated only by OAM entities operating in active OAM mode, and those
operating in passive mode wait and respond to the connection requests sent by their peers.
•
No OAM connection can be established between OAM entities operating in passive OAM mode.
After an Ethernet OAM connection is established, the Ethernet OAM entities on both sides exchange
Information OAMPDUs at a specified interval—handshake packet transmission interval—to check
whether the Ethernet OAM connection is normal. If an Ethernet OAM entity receives no Information
OAMPDU within the Ethernet OAM connection timeout time, the Ethernet OAM connection is considered
disconnected.
Link monitoring
Error detection in an Ethernet is difficult, especially when the physical connection in the network is not
disconnected but network performance is degrading gradually. Link monitoring is used to detect and
indicate link faults in various environments. Ethernet OAM implements link monitoring through the