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Chapter 20
Checking Status and Connectivity
Understanding How CFM Works with 802.3ah Link-OAM for AIS-RDI
The Ethernet Alarm Indication function (ETH-AIS) and the Ethernet Remote Defect Indication
(ETH-RDI) are new functional extensions to Metro Ethernet Connectivity Fault Management (CFM).
The ETH-AIS is a standard defined by ITU Y.1731 and the ETH-RDI is part of IEEE 802.1ag. AIS-RDI
works together to help reduce the management complexity of large SPAN networks and multiple
constituent networks that belong to separate organizations.
Ethernet Alarm Indication Signal
ETH-AIS is an important component of Ethernet-OAM. ETH-AIS is used to suppress alarms after defect
conditions are detected at the server (sub) layer.
The server (sub) layer is the virtual MEP layer. The IEEE 802.3ah OAM can detect a fault condition.
Note
AIS can differentiate between the faults at the customer level and at the provider level. The AIS serves
the following purposes:
1.
2.
3.
The main functions of the AIS module is as follows:
•
•
•
•
The CFM works with 802.3ah Finite State Machine (FSM) and has two states:
•
•
The Server MEP sends the AIS frames with the ETH-AIS information that can be enabled or disabled
on a MEP (or on a Server MEP). These frames are issued at the client's maintenance level by a MEP that
includes a Server MEP when a defect condition is detected. The defect conditions may include the
following:
•
•
OL-8978-04
Notifies the faults from the lower to the upper maintenance domain levels by potentially allowing
longer continuity check intervals to be used in the upper levels.
Suppresses the multiple redundant alarms by notifying the upper level that the fault detected
originates from a lower level.
Enables the customer to monitor service availability.
To generate the AIS protocol data units (PDUs) upon a signal fault condition that has occurred due
to an AIS defect condition.
To receive to process AIS PDUs, and to maintain an expiry timer.
To inform the continuity check module about the remote MEP connectivity path failure. The CCM
module then generates the Continuity Check Messages (CCMs) with an RDI flag set in the periodic
CCMs until the error condition is cleared.
To signal the configuration management application to suppress alarms.
SEND_ANY—The 802.3ah OAM link is up and operational. In this state, AIS PDUs are not
transmitted.
AIS—The 802.3ah OAM link has detected traffic that results in a fault condition. The AIS module
remains in a sticky state until the OAM link explicitly sends an operational trigger to clear the sticky
state. CFM periodically sends AIS PDUs until the defect condition is cleared.
The signal fail conditions when an Ethernet Continuity Check (ETH-CC) is enabled.
The AIS condition when an Ethernet Continuity Check (ETH-CC) is disabled.
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
Configuring the Alarm Indication Signal
20-55
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