Allied Telesis AT-CM70S - Manual (Page 48)

Chapter 1: Converteon™ Fast Ethernet and Gigabit Ethernet Line Cards
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ˆ Organizational Specific OAMPDUs
Organizations may define events that are of variable-length and are
distinguish by the OUI. This is a variable-length TLV.
ˆ Unsupported OAMPDUs
Unknown/unsupported OAMPDUs are sent to the OAM Client. This is
different from typical Ethernet (802.3x) behavior, which filtered
unsupported opcodes.
OAM Discovery
Discovery is the first phase of the IEEE 802.3ah OAM protocol, and relies
on what are termed information OAMPDUs. During discovery, information
about OAM entities capabilities, configuration, and identity are exchanged.
The discovery process allows a local Data Terminating Entity (DTE) to
detect OAM on a remote DTE. Once OAM support is detected, both ends
of the link exchange state and configuration information (such as mode,
PDU size, loopback support, etc.). If both DTEs are satisfied with the
settings, OAM is enabled on the link. However, the loss of a link or a
failure to receive OAMPDUs for five seconds may cause the discovery
process to restart.
This is one important aspect of the IEEE 802.3ah OAM spec is that an
OAM entity may be in either Active or Passive mode.
ˆ Active Mode – Active-mode DTEs instigate OAM communications
and can issue queries and commands to a remote station.
ˆ Passive Mode – Passive-mode DTEs generally wait for the peer
station to instigate OAM communications and respond to, but do not
instigate, commands and queries.
By default, the card should come up in Passive mode for OAM discovery
(as per the IEEE 802.3ah). In order to initiate OAM discovery, the card
should change from Passive mode to Active mode by the CPM card within
a chassis. Therefore, if a line card is in a chassis with no CPM card, it
should come up in Passive mode.
The difference between the modes is that an active-mode station can
exert more control on its peer than a passive-mode station. For example,
an active-mode OAM entity can put a passive-mode OAM entity into
loopback mode, but not vice versa.