Alcatel-Lucent 7750 Configuration Manual page 156

802.3ah OAM
Each frame error monitor functions independently of other monitors. Each of monitor
configuration includes an optional signal degrade threshold sd-threshold, a signal failure
threshold sf-threshold, a window and the ability to communicate failure events to the peer by
setting a Flag field in the Information OAMPDU or the generation of the Event Notification
OAMPDU, event-notification. The parameters are uniquely configurable for each monitor.
A degraded condition is raised when the configured signal degrade sd-threshold is reached. This
provides a first level log only action indicating a link could become unstable. This event does not
affect the port state. The critical failure condition is raised when the configured sf-threshold is
reached. By default, reaching the signal failure threshold will cause the port to enter the Link Up
condition unless the local signal failure local-sf-action has been modified to a log-only action.
Signal degrade conditions for a monitor in signal failed state will be suppressed until the signal
failure has been cleared.
The initial configuration or the modification of either of the threshold values will take affect in the
current window. When a threshold value for a monitor is modified, all active local events for that
specific monitor will be cleared. The modification of the threshold acts the same as the clear
command described later in this section.
Notification to the peer is required to ensure the action taken by the local port detecting the error
and its peer are synchronized. If peers do not take the same action then one port may remain fully
operational while the other enters a non-operational state. These threshold crossing events do not
shutdown the physical link or cause the protocol to enter a non-operational state. The protocol and
network element configuration is required to ensure these asymmetrical states do not occur.
There are two options for exchanging link and event information between peers; Information
OAMPDU and the Event Notification OAMPDU.
As discussed earlier, the Information OAMPDU conveys link information using the Flags field;
dying gasp, critical link and link fault. This method of communication has a number of significant
advantages over the Event Notification OAMPDU. The Information OAMPDU is sent at every
configured transmit-interval. This will allow the most recent information to be sent between
peers, a critical requirement to avoid asymmetrical forwarding conditions. A second major
advantage is interoperability with devices that do not support Link Monitoring and vendor
interoperability. This is the lowest common denominator that offers a robust communication to
convey link event information. Since the Information OAMPDU is already being sent to maintain
the peering relationship this method of communication adds no additional overhead. The local-sf-
action options allow the dying gasp and critical event flags to be set in the Information OAMPDU
when a signal failure threshold is reached. It is suggested that this be used in place of or in
conjunction with Event Notification OAMPDU.
Event Notification OAMPDU provides a method to convey very specific information to a peer
about various Link Events using Link Event TLVs. A unique Event Notification OAMPDU will
be generated for each unique frame error event. The intension is to provide the peer with the
Sequence Number, Event Type, Timestamp, and the local information that caused the generation
of the OAMPDU; window, threshold, errors and error running total and event running total
specific to the port.
Page 156 7750 SR Interface Configuration Guide