User's Manual

14-3
1. Ethernet OAM connection establishment
Ethernet OAM entity discovers remote OAM entities and establishes sessions with them by exchanging
Information OAMPDUs. EFM OAM can operate in two modes: active mode and passive mode. One session
can only be established by the OAM entity working in the active mode and ones working in the passive mode
need to wait until it receives the connection request. After an Ethernet OAM connection is established, the
Ethernet OAM entities on both sides exchange Information OAMPDUs continuously to keep the valid Ethernet
OAM connection. If an Ethernet OAM entity receives no Information OAMPDU for five seconds, the Ethernet
OAM connection is disconnected.
2. Link Monitoring
Fault 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 discover
link faults in various environments. EFM OAM implements link monitoring through the exchange of Event
Notification OAMPDUs. When detecting a link error event, the local OAM entity sends an Event Notification
OAMPDU to notify the remote OAM entity. At the same time it will log information and send SNMP Trap to the
network management system. While OAM entity on the other side receives the notification, it will also log and
report it. With the log information, network administrators can keep track of network status in time.
The link event monitored by EFM OAM means that the link happens the error event, including Errored symbol
period event, Errored frame event, Errored frame period event, Errored frame seconds event.
Errored symbol period event: The errored symbol number can not be less than the low threshold. (Symbol:
the min data transmission unit of physical medium. It is unique for coding system, the symbols may be
different for different physical mediums, symbol rate means the changed time of electron status per second. )
Errored frame period event: Specifying N is frame period, the errored frame number within the period of
receiving N frames can not be less than the low threshold. (Errored frame: Receiving the errored frame
detected by CRC.)
Errored frame event: The number of detected error frames over M seconds can not be less than the low
threshold.
Errored frame seconds event: The number of error frame seconds detected over M seconds can not be less
than the low threshold. (Errored frame second: Receiving an errored frame at least in a second.)
3. Remote Fault Detection
In a network where traffic is interrupted due to device failures or unavailability, the flag field defined in Ethernet
OAMPDUs allows an Ethernet OAM entity to send fault information to its peer. As Information OAMPDUs are
exchanged continuously across established OAM connections, an Ethernet OAM entity can inform one of its
OAM peers of link faults through Information OAMPDUs. Therefore, the network administrator can keep track
of link status in time through the log information and troubleshoot in time.
There are three kinds of link faults for Information OAMPDU, they are Critical Event, Dying Gasp and Link
Fault, and their definitions are different for each manufacturer, here the definitions are as below:
Critical Event: EFM OAM function of port is disabled.