Ethernet Port OAM

Overview

The Ethernet port OAM function is based on the IEEE 802.3ah EFM Ethernet OAM standards. This function mainly defines the Ethernet physical layer criteria in respect of the user access part. The Ethernet port OAM is used to handle the "last mile" problem for the Ethernet OAM. You can also use this function to check the connectivity and performance of the Ethernet physical links between two devices. If the interconnected equipment supports the 802.3ah protocol, you can monitor the accessed equipment such as modem or PON, by using the Ethernet port OAM function.

The OAM defined in the EFM standards is used to monitor the running status of links. The monitoring includes automatic discovery, connectivity check, test on delay, jitter and packet loss rate, and fault location capability improvement. Such OAM works based on ports, so it is also called port OAM. The OAM mechanism applies only to a single link, to interconnect the transport network with the access network. No end-to-end OAM mechanism can be realized.

The Ethernet port OAM protocol, as a low-rate protocol, does not affect data streams of users. The OAM occupies very narrow bandwidth and thus does not affect links greatly. The Ethernet port OAM protocol can be realized by using hardware or software because of the low rate. Also, the Ethernet port OAM protocol is independent of the transmission medium. The OAM packets are processed at only the MAC layer by using the MAC address. Therefore, other layers of the Ethernet are not affected.

The Ethernet port OAM complies IEEE 802.3ah.

Basic Concepts

• Discovery
  • Role: Discovery is the first phase of the 802.3 ah OAM protocol. Discovery identifies the supporting situation of the 802.3 ah protocol for the equipment directly connected to the local end through network cables.
  • Alarms and actions: If the negotiation fails, an alarm is reported automatically, specifying the cause of failure in detail.
  • Configuration requirement: based on ports
  • Application scenarios: fault detection and location
• Link Monitoring
  • Role: Link monitoring is used to detect and discover faults at the link layer. When the port detects performance events indicating the error frame threshold crossing, error frame second threshold crossing, and period error frame threshold crossing, this port notifies the faults by transmitting performance event notifications, that is, OAM PDU (OAM protocol data unit) packets, to the opposite equipment.
  • Alarms and actions: After you enable the port OAM function, the detection is performed automatically or you start the detection manually. Then, when receiving a remote link performance event notification, an alarm is reported.
  • Configuration requirement: based on ports
  • Application scenario: fault location
  NOTE:

  The related concepts of link monitoring are as follows.

  • Error frame: In a period, the number of error frames that exceeds the threshold value.
  • Number of period error frames: It indicates the number of error frames that exceeds the threshold value within the specified number of frames.
  • Number of error frame seconds: It indicates the number of seconds where error frames occur within the specified seconds.
  • Number of period error signals: It indicates the number of error signals within the specified number of the signals.
• Remote fault detection
  • Role: To detect remote faults based on alarm notifications from the remote end.
  • Alarms and actions: After the port OAM function at the local end is enabled and the OAM connection with the opposite end is established, when a fault that is detected at the local end, the information about the fault is transmitted to the opposite end through OAM PDUs. Thus, the fault notification is realized.
  • Configuration requirement: based on ports
  • Application scenario: fault location
• Remote Loopback
  • Role: To detect the bidirectional connectivity of a link and then loop back all data packets of the remote port. To request for remote loopback at the opposite port, the local port transmits the remote loopback OAM PDU to the opposite port. The loopback check is periodically performed to ensure that the existing links are available. In addition, the specific faulty area can be located through multi-period loopback check.
  • Alarms and actions: After the port OAM function at the local end is enabled and the OAM connection with the opposite end is established, when a remote link fault event notification is received, an alarm is reported at the local end.
  • Configuration requirement: based on ports
  • Application scenario: fault location
  NOTE:

  In the loop mode, all the packets, excluding the OAM PDU and suspending packets, are returned according to the original routes.
• MIB variable retrieval
  • Role: To query the link performance of the opposite end.
  • Alarms and actions: Manually originated
  • Configuration requirement: based on ports
  • Application scenario: fault location
• The OAM working modes include the active and passive modes.
  • Active: Active mode, in which the port can initiate OAM packets.
  • Passive: Passive mode, in which the port cannot initiate OAM packets. In this case, the port only responds to the OAM PDUs in the active mode transmitted by the opposite port.

Application

The Ethernet port OAM function is mainly used to check the connectivity of the physical link between two ports that are directly connected.

The Ethernet port OAM function is a method of checking the connectivity and performance of the physical link. The Ethernet port OAM is mainly used at the Ethernet ports that are directly connected by using Ethernet cables. See the access layer in Figure 1. The end-to-end inter-NE check is not provided.

Figure 1 Application scenario of the Ethernet port OAM function