Ethernet Connectivity Fault Management (ETH-CFM)
Page 112 7750 SR OS Services Guide
ETH-AIS
Ethernet Alarm Indication Signal function (ETH-AIS) is used to suppress alarms at the client (sub)
layer following detection of defect conditions at the server (sub) layer. Due to independent
restoration capabilities provided within the Spanning Tree Protocol (STP) environments, ETH-
AIS is not expected to be applied in the STP environment.
Transmission of frames with ETH-AIS information can be enabled or disabled on a MEP.
Frames with ETH-AIS information can be issued at the client MEG Level by a MEP, including a
Server MEP, upon detecting the following conditions:
• Signal failure conditions in the case that ETH-CC is enabled.
• AIS condition in the case that ETH-CC is disabled.
For a point-to-point ETH connection at the client (sub) layer, a client layer MEP can determine
that the server (sub) layer entity providing connectivity to its peer MEP has encountered defect
condition upon receiving a frame with ETH-AIS information. Alarm suppression is
straightforward since a MEP is expected to suppress defect conditions associated only with its peer
MEP.
For multipoint ETH connectivity at the client (sub) layer, a client (sub) layer MEP cannot
determine the specific server (sub)layer entity that has encountered defect conditions upon
receiving a frame with ETH-AIS information. More importantly, it cannot determine the
associated subset of its peer MEPs for which it should suppress alarms since the received ETH-
AIS information does not contain that information. Therefore, upon reception of a frame with
ETH-AIS information, the MEP will suppress alarms for all peer MEPs whether there is still
connectivity or not.
Only a MEP, including a Server MEP, is configured to issue frames with ETH-AIS information.
Upon detecting a defect condition the MEP can immediately start transmitting periodic frames
with ETHAIS information at a configured client MEG Level. A MEP continues to transmit
periodic frames with ETH-AIS information until the defect condition is removed. Upon receiving
a frame with ETH-AIS information from its server (sub) layer, a client (sub) layer MEP detects
AIS condition and suppresses alarms associated with all its peer MEPs. A MEP resumes alarm
generation upon detecting defect conditions once AIS condition is cleared.
Specific configuration information required by a MEP to support ETH-AIS is the following:
• Client MEG Level — MEG level at which the most immediate client layer MIPs and
MEPs exist.
• ETH-AIS transmission period — Determines transmission periodicity of frames with
ETH-AIS information.
• Priority — Identifies the priority of frames with ETH-AIS information.
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