Ethernet Continuity Check (ETH-CC)
Confined to a domain or VLAN, multicast IEEE 802.1ag Ethernet Continuity Check (ETH-CC) heartbeat messages are exchanged periodically between endpoints, thereby allowing them to discover each other or any intermediary devices. These OAM messages can detect the loss of a link and incorrect network connections. When these connectivity failures occur within a specific maintenance association, ETH-CC and can be used to trigger protection switching within 3.33ms. Hardware and software faults can also be detected with continuity check messages.
Ethernet Delay Measurement (ETH-DM)
The IEEE 802.1ab frame delay measurement (ETH-DM) function is used for on-demand operation administration and maintenance (OAM). ETH-DM is employed when measuring the frame delay (FD) and frame delay variation (FDV), where the FD refers to the interval between the time when the first bit of a frame is transmitted by a source node and the time when the last bit of the frame is received by the same source node after the frame is looped back. Frame loopback is performed by the destination node of the test. ETH-DM allows the FD and FDV measurements to be performed on each endpoint in two distinct modes: one way, or unidirectional, where the endpoint clocks are not synchronized and two-way, or bidirectional, where they are.
Ethernet Frame Loss Measurement (ETH-LM)
One of the key objectives of OAM is to measure quality-of-service (QoS) attributes, such as frame delay, frame delay variation (“frame jitter”) and frame loss. Such measurements enable you to identify network problems before customers are impacted by network defects. IEEE 802.1ab Ethernet frame loss measurement (ETH-LM) operates between associated end points configured on either physical Ethernet or logical VLAN interfaces. Near end and far end frame loss measurements are performed by sending frames with ETH-LM information to a peer endpoint and similarly receiving frames with ETH-LM information from the that peer. This type of frame loss measurement is also known as single-ended Ethernet loss measurement.
Ethernet Linktrace (ETH-LT)
The IEEE 802.1ab Ethernet linktrace (ETH-LT) function is primarily responsible for restarting the adjacency relationship and helping to locate faults. Otherwise known as a MAC trace route, ETH-LT are multicast messages that a source endpoint sends to track the hop-by-hop path to a destination device. Within a 5 second period, each intermediate device the received the linktrace datagram returns a trace route reply to the originating equipment and regenerates the ETH-LT message on to its destination. The ETH-LT PDU includes fields for a Transaction ID, Time-to-Live (TTL), origin and target MAC addresses.
Ethernet Loopback (ETH-LB)
The IEEE 802.1ab ETH-LB is unicast message used to check whether a fault occurs on the link between the local and peer terminal equipment. On receiving the loopback message, the endpoint checks whether conditions are met. If so, the receive node returns a loopback reply (LBR) packet (another unicast MAC message) to the originating device. The source node reports an alarm if it does not receive any LBR within five seconds after sending the LBM. As intermediate nodes perform only Layer 2 forwarding, LBMs can carry additional data that must be returned in LBRs without change. LBMs can therefore also be used for traffic test purposes.