Ethernet Oam Configuration; Introduction; Ethernet Oam: Main Operating Points; Accessing The Ethernet Oam Configuration Menu - Teldat Dm709-I User Manual

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Chapter 9 Ethernet OAM Configuration

9.1 Introduction

Ethernet OAM (Operations, Administration and Maintenance, IEEE 802.3 ah EFM) is a layer 2 protocol (designed as
a sublayer in the link layer, in accordance with the OSI model) that provides performance monitoring, remote failure
indication and loopback testing in an Ethernet link. It is meant to operate in full-duplex point-to-point Ethernet links in
EFM (Ethernet in the First Mile) environments.

9.1.1 Ethernet OAM: Main operating points

The Ethernet OAM protocol doesn't generate a significant traffic load in Ethernet interfaces, as it requires little band-
width to operate (it's known as a slow protocol).
The protocol starts with a discovery phase where a local station transmits OAM information packets (OAMPDUs), de-
scribing the functionalities and the configuration of the local OAMs. At the same time, it detects the presence of a re-
mote OAM station by receiving OAMPDUs from the other end of the link. This phase provides the opportunity for
both stations to accept or reject the OAM configuration available at the remote station.
Amongst the information exchanged during the discovery phase, the following is worth noting:
• Operating mode: active or passive.
• Available operations: link and remote loopback monitoring, etc.
• Maximum size allowed for an OAMPDU.
• Platform identification.
Once the OAM session is established, both stations must send information OAMPDUs to maintain the session. If
OAMPDUs are not received after a certain time, an OAM station restarts the OAM session and returns to the discov-
ery phase.
An OAM station can operate in two modes: active and passive. Only an active station can start the discovery phase
by sending an information OAMPDU. Therefore, a station configured as passive must wait to receive an information
OAMPDU to start transmitting OAMPDUs with local information. An OAM session is also possible with both link sta-
tions in active mode.
An OAM station in passive mode must fulfill certain rules. The following should be noted:
• It must wait for the remote station to start the discovery phase (as already commented).
• Control commands in loopback mode cannot be sent from the remote station.
• It cannot send MIB variable petitions.
One of the main points of Ethernet OAM is link monitoring. This feature is implemented through the sending of event
notification OAMPDUs, which contain information on the traffic-related error statistics received in the interface. These
statistics often contain the received frame and symbol errors. Likewise, there are flags reserved in an OAMPDU used
to advise the remote station on critical events in the link. The definition of the events activating these flags is not spe-
cified in the IEEE norm and falls under the implementer's responsibility.
To round off, we are going to describe the Ethernet OAM loopback operation. An OAM station, configured in active
mode, can send an order to the remote station to set it in loopback mode (provided said station allows this opera-
tion). Loopback control commands are transmitted through a specific type of OAMPDUs. When an OAM station is in
loopback mode, any packet received by the interface that is not OAMPDU is returned unaltered. Loopback was de-
veloped to be used when installing a link or to resolve problems in the link.

9.2 Accessing the Ethernet OAM Configuration menu

Accesses OAM configuration from an Ethernet interface through the oam command. The configuration can be activ-
ated from both the Config process (static configuration, active after restarting the device) and the running-config pro-
cess (dynamic configuration).
Example:
*config
Config>network ethernet0/1
-- Ethernet Interface User Configuration --
ethernet0/1 config>oam
LAN Interfaces

9 Ethernet OAM Configuration

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