DELL S50V User Manual

802.3ah | 93

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A metropolitan area network (MAN) is a set of LANs, geographically separated but managed by a single 
entity. If the distance is large—across a city, for example—connectivity between LANs is managed by a 
service provider. While LANs use Ethernet, service providers networks use an array of protocols (PPP and 
ATM), and a variety access technologies. Implementing Ethernet from end to end, across the service 
provider network, simplifies design and management, increases scalability and bandwidth, and reduces 
costs. 

Ethernet in a service provider environment introduces the concept of Carrier-class Ethernet and requires 
some basic management and diagnostic tools. Ethernet Operations, Administration, and Maintenance 
(OAM) is that toolset, which can be used to install, monitor, troubleshoot, and manage Ethernet 
infrastructure deployments. It consists of three main areas:

1. Service Layer OAM: IEEE 802.1ag, Connectivity Fault Management (CFM)

2. Link Layer OAM: IEEE 802.3ah, Ethernet in the First Mile (EFM) OAM

3. Ethernet Local management Interface (MEF-16 E-LMI)

Link Layer OAM introduces the toolset required to effectively monitor the link between the customer and 
service provider, which is called the first mile. Currently, service providers use a variety of access 
technologies including ISDN, DSL, and coax cable in the first mile. Implementing Ethernet here reduces 
the types of equipment in the subscriber access network, simplifying installation and management, and 
increasing bandwidth.

Link Layer OAM performs four primary operations for the purposes of link status, performance 
monitoring, and fault detection and isolation for Ethernet in the First Mile:

OAM Discovery—detects whether the remote system is OAM capable, and negotiates OAM 
parameters.

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Link Event Monitoring—defines a set of events that may impact link operation, and monitors the link 
for those events.