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Remote trouble indication

It is difficult to check troubles in the Ethernet, especially the case that the

network performance slows down while physical network communication

continues. OAM PDU defines a flag domain to allow Ethernet OAM entity to

transmit the trouble information to the peer. The flag can stand for the

following emergent link events:

Information OAM PDU is continuously transmitted during Ethernet OAM

connection. The local OAM entity can report local critical link events to

remote OAM entity through Information OAM PDU. The administrator thus

can dynamically know the link's state and handle corresponding errors in

time.

Remote loopback

OAM provides an optional link-layer-level loopback mode and conducts

error location and link performance testing through non-OAM-PDU

loopback. The remote loopback realizes only after OAM connection is

created. After the OAM connection is created, the OAM entity in active

mode triggers the remote loopback command and the peer entity responses

the command. If the remote terminal is in loopback mode, all packets

except OAM PDU packets and Pause packets will be sent back through the

previous paths. Error location and link performance testing thus can be

conducted. When remote DTE is in remote loopback mode, the local or

remote statistics data can be queried and compared randomly. The query

operation can be conducted before, when or after the loopback frame is

transmitted to the remote DTE. Regular loopback check can promptly

detect network errors, while segmental loopback check can help locating

these network errors and then remove these errors.

Round query of any MIB variables described in chapter 30 of 802.3.

1.1.2 OAM Mode

The device can conduct the OAM connection through two modes: active mode

and passive mode. The device capacity in different mode is compared in table 2.

Only OAM entity in active mode can trigger the connection process, while the

OAM entity in passive mode has to wait for the connection request from the peer

OAM entity. After the remote OAM discovery process is done, the local entity in

active mode can transmit any OAM PDU packet if the remote entity is in active

mode, while the local entity's operation in active mode will be limited if the remote

entity is in passive mode. This is because the device in active mode does not

react on remote loopback commands and variable requests transmitted by the

passive remote entity.

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Link Fault: The physical layer detects that the reception direction of the

local DTE has no effect. If troubles occur, some devices at the physical

layer support unidirectional operations and allows trouble notification

from remote OAM.

Dying Gasp: If an irrecoverable local error occurs, such as OAM

shutdown, the interface enters the error-disabled state and then is

shut down.

Critical Event: Uncertain critical events occur (critical events

specified by the manufacturer).

Table 2 Comparing device capacity in active and passive modes

OAM Configuration

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