User's Manual

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Users Manual of CS-6306R
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:
 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 are specified by the manufacturer).
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.
33.1.1.2 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.
Table 2 Comparing device capacity in active and passive modes
Capacity Active Mode Passive Mode
Initializing the Ethernet OAM discovery process Yes No