MEF 2 allows the MEN to leverage any
underlying transport layer protection type if it can enable end-to-end service protection.
Table 2.4 identifies key standards based developments that are incorporating
Reliability.
Two protection types, 1+1 and M:N, have been defined. In the 1+1 approach, duplicate
traffic is the norm, and in the case of a failure/protection event, one stream of traffic
is still available (unless the failure is catastrophic). In the case of M:N, N working resources
are provided protection using M protection sources.
Four different protection mechanisms have also been defined: Aggregate Link and
Node Protection (ALNP) to protect against local link/node failure; End-to-End Path
Protection (EEPP), where redundancy is provided for the primary path on an endto-
end basis; MP2MP protection of E-LAN services including Rapid Spanning Tree
Protocol (RSTP) and link redundancy; and finally, link protection based on link aggregation,
where one or more Ethernet links connected between the same nodes can
be aggregated.
Carrier Ethernet 85
MEF 2 has provided for supporting a wide variety of restoration times, from less than
5 seconds to the less than 50 ms range, in order to support the wide variety of applications
and their corresponding requirements.
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