Foundry NetIron M2404C and M2404F Metro Access Switches
Network Administration Tools (Rev. 03)
Intermediate 802.3ah EFM OAM
© 2008 Foundry Networks, Inc.
Page 54 of 155
Intermediate 802.3ah EFM OAM
Overview
The IEEE 802.3ah Ethernet in the First Mile (EFM) standard specifies the protocols and Ethernet
interfaces for using Ethernet over access links as a first-mile technology and
transforming it into a
highly reliable technology.
Using the Ethernet in the First Mile solution, the user will gain broadcast Internet access, in
addition to services, such as Layer 2 transparent LAN services, Voice services over Ethernet
Access networks, and Video and multicast applications, reinforced by security and Quality of
Service control in order to build a scalable network.
The in-band management specified by this standard defines the operations, administration and
maintenance (OAM) mechanism needed for the advanced monitoring and maintenance of Ethernet
links in the first mile. The OAM capabilities facilitate network operation and troubleshooting.
Basic 802.3 frames convey OAM data between two ends of the physical link. EFM OAM is
optional and can be disabled on each physical port.
OAM initiatives are classified into three layers:
transport, connectivity
and
service
. The transport
layer is the collection of forwarding entities and interconnected segments that form a multi-hop
Ethernet network, and provide connectivity between devices. The transport layer OAM is specified
by the IEEE 802.3ah (Clause 57) and provides single-link OAM capabilities. When OAM is
present, two connected OAM sub-layers exchange protocol data units (OAMPDUs). OAM PDUs
are standard-size frames that can be sent at a maximum rate of 10 frames per second. This
limitation is necessary for reducing the impact on the usable bandwidth. It is possible to send each
frame several times in order to increase the probability of reception. A combination of the
destination MAC address, the Ethernet type/length field and Subtype allow distinguishing
OAMPDU frames from other frames.
OAM functionality is designed to provide reliable service assurance mechanisms for both provider
and customer networks.
The IEEE 802.3ah EFM standard offers an opportunity to create the operations, OAM sub-layer
within the data-link layer of the OSI protocol stack. The data-link layer provides utilities for
monitoring and troubleshooting Ethernet links.
Figure 8: End-to-End OAM Configuration