802.3ah | 95Link Layer OAM Operational ModesWhen participating in EFM OAM, system may operate in active or passive mode.• Active mode—Active mode systems initiate discovery. Once the Discovery process completes, theycan send any OAMPDU while connected to a peer in Active mode, and a subset of OAMPDUs if thepeer is in Passive mode (see Table 6-1).• Passive mode—Passive mode systems wait for an active mode system to initiate discovery, and do notsend Variable Request or Loopback Control OAMPDUs.Taken from IEEE 802.3ah, Table 6-1 summarizes the permitted actions in each role.Link Layer OAM DiscoveryOAM Discovery is the mechanism a Link Layer OAM-capable system uses to determine if the remotesystem on the link has OAM functionality enabled. OAM Discovery ascertains OAM parameters, such asmaximum allowable OAMPDU size, and supported functions such as OAM remote loopback.The discovery process is as follows:1. If the link is not in Fault state, Active mode systems send Information OAMPDUs that contain (only)the Local Information TLV.2. Once a system receives an Information OAMPDU, it responds with an Information OAMPDU thatcontains the Local and Remote Information TLV. Negotiation is complete when both systems havereceived their peer’s information and are satisfied with it; to be satisfied, both peers on the link must behave link performance event monitoring enabled.3. When negotiation is complete, both peers may send any type of OAMPDU.Table 6-1. Active Mode and Passive Mode BehaviorsCapability Active PassiveInitiates OAM Discovery process Yes NoReacts to OAM Discovery process initiation Yes YesRequired to send Information OAMPDUs Yes YesPermitted to send Event Notification OAMPDUs Yes YesPermitted to send Variable Request OAMPDUs Yes NoPermitted to send Variable Response OAMPDUs (the peer must be in Active mode) Yes YesPermitted to send Loopback Control OAMPDUs Yes NoReacts to Loopback Control OAMPDUs (the peer must be in Active mode) Yes YesPermitted to send Organization Specific OAMPDUs Yes Yes
