OAM Related Questions
1. How is EFM OAM different from IEEE 802.1ag?
Connectivity Fault Management (CFM, as defined in IEEE P802.1ag) is one component of the overall plan for enabling Service Providers to offer Service Instances (Ethernet Layer 2 services) to Customers. CFM provides a set of protocols and procedures that provide fault detection and isolation capabilities for very large Layer 2 networks, perhaps by multiple organizations.
IEEE 802.3ah OAM specification covers the OAM frames used across a physical IEEE 802.3 medium between a Provider and a Customer, or perhaps between two Provider ports or two Customer ports. This is a very important part of the overall Connectivity Fault Management picture.
2. How is EFM OAM different from SNMP?
Ethernet OAM is complementary, not competitive, with SNMP management in that it provides some basic management functions at layer two, rather than using layer three and above as required by SNMP over an IP infrastructure. Ethernet OAM provides single-hop functionality in that it works only between two directly connected Ethernet stations. SNMP can be used to manage the Ethernet OAM interactions of one Ethernet station with another.
From: M. Squire, draft-ietf-hubmib-efm-mib-02.txt, copyright © 2004 IETF.
3. Why can EFM OAM only be used to read MIB variables, and not to write them?
EFM OAM does not deal with configuration that is required for normal operation. Port types that require some kind of configuration in order to operate normally, use dedicated protocols within the physical layer for this purpose (e.g., G.994.1 handshake for 2BASE-TL and 10PASS-TS, MPCP for EPON). Beside the objects required for normal operation, there are few objects in the physical layer that are worth writing remotely. It was therefore decided not to burden the OAM variable retrieval protocol with this extra complexity.
Higher-layer management protocols that have writeable objects in their MIB, such as SNMP, may be used to set variables in remote nodes.
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